# 5mm LED Lumens Output



## Farhaj (Apr 28, 2014)

Can someone tell me or calculate out for me the LUMENS/ Luminous flux (lm) For this White 5mm LED.. The datasheet Link is Below.

http://underwaterseaplants.awardspace.com/led.pdf

I would be really thankful to you. This LEDs is being used in a Flash Light..


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## RoGuE_StreaK (Apr 28, 2014)

Candela don't really convert to lumens well, but according to this wizard a rough guestimation of 10,000 mcd @ 15degree beam is about 0.6lumens, @30degree beam about 2lumens, so that gives you an extremely rough ballpark.


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## Farhaj (Apr 28, 2014)

RoGuE_StreaK said:


> Candela don't really convert to lumens well, but according to this wizard a rough guestimation of 10,000 mcd @ 15degree beam is about 0.6lumens, @30degree beam about 2lumens, so that gives you an extremely rough ballpark.



I read that formula is only good for the Green LED with a different Wavelength than the WHite One.. for the White LED their needs to be weighting attached to it.. Any idea how it would work out...


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## DollarIn (Apr 28, 2014)

Farhaj said:


> I read that formula is only good for the Green LED with a different Wavelength than the WHite One.. for the White LED their needs to be weighting attached to it.. Any idea how it would work out...


No, its the same for all wavelengths.


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## Farhaj (Apr 28, 2014)

DollarIn said:


> No, its the same for all wavelengths.



See this PAge.. Where it says a weighting should be applied.. here is the Link,.. http://www.compuphase.com/electronics/candela_lumen.htm

this is what it refers to,,,
_
"""_[h=2]_Evaluation_[/h]_The outcome of the equations (and the calculators based on them) may differ from the data given by a LED or spotlight manufacturer, or from what you measure with a Lux meter, for several reasons. The manufacturer may specify the luminous intensity (in candela or milli-candela) perpendicular to the light source, instead of the average value over the apex angle. Another complexity is that the values for candela, lumen and lux are standardized for light with a wave length of 555 nm, or green light. For LEDs of a different colour, a weighting function should be applied, using a standardized model of the human eye. Standard Lux meters have, at best, only filters for daylight and incandescent light, and may therefore deviate significantly for LEDs (even white LEDs, as the spectrum is not the same as for incandescent lamps)."""""_


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## alpg88 (Apr 28, 2014)

RoGuE_StreaK said:


> Candela don't really convert to lumens well, but according to this wizard a rough guestimation of 10,000 mcd @ 15degree beam is about 0.6lumens, @30degree beam about 2lumens, so that gives you an extremely rough ballpark.



you can't convert like that. mcd rating is highly dependant of the angle. at 30* same led will not have same mcd as at 15*.


usually those leds around 30 lm/w, those are good ones cree and nichia, no name leds would be less


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## DollarIn (Apr 28, 2014)

Farhaj said:


> See this PAge.. Where it says a weighting should be applied.. here is the Link,.. http://www.compuphase.com/electronics/candela_lumen.htm
> 
> this is what it refers to,,,
> _
> ...


That applies to measuring light, not converting between candela and lumens. If you're measuring candela or lumens the wavelength of the light is important. but if you already know the value, it's a simple calculation.


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## Farhaj (Apr 28, 2014)

DollarIn said:


> That applies to measuring light, not converting between candela and lumens. If you're measuring candela or lumens the wavelength of the light is important. but if you already know the value, it's a simple calculation.



Ok so how do u measure light then .. measuring light is also in lumens right..? and how the calculation is done using the wave length,,,


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## JohnR66 (Apr 28, 2014)

5mm LEDs are often measured in intensity (candelas). This is good for comparing 5mm LEDs as long as the the beam angle is taken into consideration. Why do you need lumens? The brightest, reasonably priced obtainable 5mm LEDs are the Cree C503D series. They are typically 40,000cd (confirmed on my light meter) at a 15 Deg beam angle. I don't have the equipment to measure the lumens.


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## Farhaj (Apr 29, 2014)

JohnR66 said:


> 5mm LEDs are often measured in intensity (candelas). This is good for comparing 5mm LEDs as long as the the beam angle is taken into consideration. Why do you need lumens? The brightest, reasonably priced obtainable 5mm LEDs are the Cree C503D series. They are typically 40,000cd (confirmed on my light meter) at a 15 Deg beam angle. I don't have the equipment to measure the lumens.



Their are some Forumlas to calculate Lumens.. DO you know any of those... I want to know coz of the Light Output Lumens from the flashlight...


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## alpg88 (Apr 29, 2014)

5mm leds are around 3-5lm. some manufacturers still make keychain lights with 5mm leds, they also rate them by lumens
http://www.photonlight.com/led-flashlights/photon-micro-light-ii-led-keychain-flashlight/


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## Farhaj (Apr 29, 2014)

alpg88 said:


> 5mm leds are around 3-5lm. some manufacturers still make keychain lights with 5mm leds, they also rate them by lumens
> http://www.photonlight.com/led-flashlights/photon-micro-light-ii-led-keychain-flashlight/



some even say are in 7-8 Lumens.. some calculations as per datasheet or results would be more helpful and valid...


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## alpg88 (Apr 29, 2014)

Farhaj said:


> some even say are in 7-8 Lumens.. some calculations as per datasheet or results would be more helpful and valid...



no, calculations are not as good as acually mesuring output in lightsphere, as pbly manufactures did, before putting lumen number on the box.

but we will be interesting to see what your calculations find, let us know when you fiinish calculations


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## JohnR66 (Apr 29, 2014)

alpg88 said:


> no, calculations are not as good as acually mesuring output in lightsphere, as pbly manufactures did, before putting lumen number on the box.



This is correct. Unless the light intensity follows a simple mathematical curve across its beam angle or is flat, it would be difficult to figure without lots of sample points. Also, some light is emitted from the sides and behind the LED.


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## TEEJ (Apr 29, 2014)

There is no way to directly measure lumens.

Lumens are CALCULATED from the lux, and, that lux has to be measured in a device that spreads the lumens out evenly, so that no one spot is brighter than another. (The device is called an Integrating Sphere (IS), and, amateurs attempt to approximate this with various homemade versions. )

A LUX measurement is then made of that homogeneous light, based upon the assumption that all areas measured yield the same lux reading as the light is homogeneous.

Lumens = Lux per square meter, so, knowing the surface area if the IS (the square meters), and the lux, you can CALCULATE the lumens from that lux reading.

In real life, without a real IS, its actually almost impossible to get a truly homogeneous distribution of light, and, therefore, depending upon the exact spot chosen to measure, the lux levels tend to differ, which changes the calculated lumen estimates.


So, other than using an IS, there is no DIRECT way to convert lux or cd to lumens, any more than you could DIRECTLY convert speed to horsepower. (You'd need more information, and then be able to calculate it, etc...)


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## alpg88 (Apr 29, 2014)

well if you want to go into specifics, no dmm mesures volts or resistance, all it does is mesures current. but depending on the settings, it calculates values you are looking for. 
same with lightbox, it may mesure lux, but it mesures it, so calculation to get lumens will be based or real performance of that specific led.


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## TEEJ (Apr 29, 2014)

alpg88 said:


> well if you want to go into specifics, no dmm mesures volts or resistance, all it does is mesures current. but depending on the settings, it calculates values you are looking for.
> same with lightbox, it may mesure lux, but it mesures it, so calculation to get lumens will be based or real performance of that specific led.



Not in this case. The DMM can at least mathematically interpret other values, but, its getting the entire signal to work with. The lux or cd you get is NOT the entire signal.

So, sure, you can be given a cd value someone measured quite accurately....but, there's no way to take a lux value that represents ONLY THE HOTTEST PART OF A HOT SPOT, and have it tell you the lux that you would have gotten to the side of the hottest part of the hot spot, or the corona or the spill, etc....

I can have a light with a cd of 100,000, and it could be one lumen, or a million lumens, there's no relationship between the numbers themselves.

I could have a light with 1,000 lumens, and a cd of 100 or a cd of a million, again, there's no relationship between the numbers themselves....they are simply not representing the same thing.



Its like being told the thickness of the paint on a small piece of wood, and being asked to tell how large a container of paint the paint came from.

They can give you thickness down to the last Aº unit, the most accurate thickness measurement you can get....and you STILL have no way of knowing if the paint came from a 1 qt can, a 1 gal or 5 gal pail....the numbers are simply not related to each other.


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## alpg88 (Apr 29, 2014)

do you know how lightsphere works????


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## TEEJ (Apr 29, 2014)

alpg88 said:


> do you know how lightsphere works????



If you mean an IS as referred to in my post above, yes.

As I mentioned a few times...if they use one you HAVE the lumens. ..and don't need to ask how to convert.


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## Farhaj (Apr 30, 2014)

there are forumlas given on this page to convert various data into Lumens.. I used this http://www.rapidtables.com/calc/light/how-candela-to-lumen.htm
and forund the results per led to 0.54 lm.. which is not at all possible in the real LED. so low.. 
then, I found out that theformula is good for only upto certain limit of wavelengths in LED.. not for the white LEDS.. 
I do not know the realty..

can you now excplain..


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## Farhaj (Apr 30, 2014)

Also, I have I some data and pictures of LED..
























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## TEEJ (Apr 30, 2014)

THERE IS NO CONVERSION.

If ALL you know is the cd or lux, etc, you cannot (CAN NOT) plug in that number and get the lumens.

THAT is why it "doesn't work".



Again, lux is the lumens per square meter...so, you need to know the square meters the lux is on to back calculate the lumens.

The PROBLEM is that you ALSO need to know the lux on EVERY PART of that square meter, and, no LED or incan, etc, emits lumens in a homogeneous pattern, so that no matter where you measure the lux, it will be the same. You NEED the light to be homogeneous to get a REPRESENTATIVE measurement of the lux.


THAT is what the IS (Integrating Sphere) is FOR, to GET a homogeneous distribution, so you CAN take a REPRESENTATIVE measurement.


When they measure the cd, mcd, etc...its measured at the hottest point in the output...not an average of the beam...so, that's the "brightest" part of the beam, the beam is MOSTLY dimmer than that....and, that is "where most of the lumens are"...in the part that was NOT measured.



So, again, you *CAN NOT *take a known cd or mcd, etc... and *plug it into a formula* to get lumens.

You can't do it.


If you have a device to make the lux exactly the same no matter where its measured - THEN you can take a lux measurement that CAN be plugged in, as its merely lumens per square meter = lux.

Of course, if you HAVE that, you already KNOW the lumens, as that's WHAT the IS will tell you.


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## alpg88 (Apr 30, 2014)

TEEJ said:


> When they measure the cd, mcd, etc...its measured at the hottest point in the output...not an average of the beam...



actually exact opposite is true. light is NOT mesured at the hottest point in the output. 
http://www.candlepowerforums.com/vb/showthread.php?200334-Building-an-Integrating-Sphere


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## LEDninja (Apr 30, 2014)

I replied to a PM the OP sent me:

"The data sheet is for a 5mm LED. They were designed in the 1990s and are very dim by today's standards. So how many LEDs are in the flashlight?

The spec sheet says 60mW or 0.06 watts. Multiply 0.06 by the number of LEDs to get the approximate watts.

The brightness is given in MCD. There is no easy conversion from MCD to Lumens. 5mm LEDs run from 3 lumens to 12 lumens. My guess is multiply 3 by number of LEDs to get Lumens for the flashlight.
(The spec sheet says 20 mA normal 75 mA max. The LEDs will burn out very fast if run at 75 mA so I expect the flashlight will run the LEDs at 20 mA each giving you about 3 lumens per LED.)

The manufacturer may not be using 20 mA or 60 mW so any calculations you make are still guesses."

Now I see 12 LEDs.
My guess is:
Wattage ~0.72W;
Lumens ~36 lumens.


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## DollarIn (Apr 30, 2014)

TEEJ said:


> If ALL you know is the cd or lux, etc, you cannot (CAN NOT) plug in that number and get the lumens.


The key word is IF.

It's like if you know you've travelled a distance of exactly 100km, it's impossible to determine your average speed. If you know approximately how long it took, e.g. 1 hour, you can some up with a reasonably accurate estimate. The analogy with the DMM is more appropriate, but has already been used...

For a 5mm LED you can approximate the beam angle. Better yet you can measure it, and then calculate the lumens from the cd. For all practical purposes that will be enough given the expected variance of datasheet values. If you want a more accurate value, use an integrating sphere.


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## RoGuE_StreaK (Apr 30, 2014)

Farhaj said:


> Also, I have I some data and pictures of LED..


I don't get it; you go through all this rigmarole of asking about formulas, rejecting everyone's inputs, providing specsheets in candela, and then produce something that _*specifically states the luminous flux *_(7.58lm), then ignore what you've posted?!

If this is to backup your lumen claims for a commercial product, then pay for someone to properly test it


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## TEEJ (Apr 30, 2014)

alpg88 said:


> actually exact opposite is true. light is NOT mesured at the hottest point in the output.
> http://www.candlepowerforums.com/vb/showthread.php?200334-Building-an-Integrating-Sphere



No IT IS measured at the hottest point. (cd is measured at the hottest point to GET THE cd)

What you are talking about is IN AN IS, which homogenizes the light, and, which is the only time you can get lumens numbers from lux numbers. (IE: There IS no hot spot, BECAUSE the sphere's JOB is to homogenize the light.



The problem with this thread is that the OP is trying to do a conversion, and there isn't one.

By posting about integrating spheres, its confusing the issue, and giving the wrong answer to his actual question.

IE: IF a sphere was used, he would not NEED to convert anything...as the SPHERE'S measurement GIVES the lumens.


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## Farhaj (May 1, 2014)

RoGuE_StreaK said:


> I don't get it; you go through all this rigmarole of asking about formulas, rejecting everyone's inputs, providing specsheets in candela, and then produce something that _*specifically states the luminous flux *_(7.58lm), then ignore what you've posted?!
> 
> If this is to backup your lumen claims for a commercial product, then pay for someone to properly test it




Where does it mention about the 7.58lm.. I did not find it...


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## Farhaj (May 1, 2014)

LEDninja said:


> I replied to a PM the OP sent me:
> 
> "The data sheet is for a 5mm LED. They were designed in the 1990s and are very dim by today's standards. So how many LEDs are in the flashlight?
> 
> ...




Yesterday, I sat and did some measurements for the FLASHLIGHT.. I calculated out the *VOLTS and Resistance for Each Mode ( 1 & 2) *... 




Can you guys now have a look and tell me what would be Its *WATTS, LUMENS and AMPERES EXACTLY..*.




The areas of the Battery Side along with the Circuit photo is attached along as well; to get a more clearer image of the Volts in the Battery produced.




Have a look at the readings and the PICS Below:


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## TEEJ (May 1, 2014)

Sigh.

:fail:


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## Farhaj (May 2, 2014)

So any reply guys on how to now get the answers to questions after now I have done detailed readings as well..


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## Farhaj (May 3, 2014)

I did some more Calculations from the Measurements I did Earlier to calculate the watts and Amperes more Precisely..*Can this now help more in calculation of total lumens for light..*







1) Now, after so many results and Measurements can we get to a closer value of the LUMENS for the Flash Light ..
2) Secondly they claim that it is a *1 Watts* Flash Light but through Calculations we found out that; it is* 1.1482 Watts* .. *Slightly higher*.. either we are or wrong, or they are..?
3) Why this Formula Mentioned here is not efficient or not suitable for calculation of Lumens for this White Straw Hat LED Flashlight.. or is it suitable..If, not then for what purpose is it used...? http://www.rapidtables.com/calc/light/mcd-to-lumen-calculator.htm


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## TEEJ (May 3, 2014)

Please stop.

You don't understand your question, and keep showing info that indicates you are not understanding your question.

You are not asking an answerable question, as there is no relationship between candelas and lumens that allows you to know one, and derive the other.

IF the maker lists the lumens, then, you read them off the chart. LOOK at the chart, if you SEE lumens, you know, for that LED, the lumens.



To CALCULATE lumens from lux or candelas though, you can't ONLY know candelas and figure out the lumens.




The ONE way that CAN be done is a DEVICE is use that is DESIGNED to measure EVENLY DISTRIBUTED lux, and calculate the lumens. As the specs from an LED CAN include the lumen output under certain power and temperature/humidity conditions, that is your best bet. If they don't supply it, but ONLY supply the candelas, you CANNOT derive the lumens.

IE: If you have a known surface area lux is ON, and, a way to make the lux read the same all across that surface area...AND that surface area is accounting for ALL the light being produced, THEN, and only then, can you calculate the lumens from the lux.


The ROOT problem you are facing is that the cd specs are taken NOT as a homogenized reading, over a known surface area, but, instead, as a MAXIMUM reading, at the highest point in the output, with NO known surface area....and therefore cannot (CAN NOT) be used.


Right now, you are saying something like: "Here are charts showing how many horsepower various engines have. I want to know how much torque they have, so, please tell me how to calculate the torque if I know the horsepower?"






To take a new tack, the lumens are what you can't SEE, and, the lux is often more useful anyway.

What is your application, and, how much lux do you need on whatever is supposed to be illuminated?


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## RoGuE_StreaK (May 3, 2014)

Farhaj said:


> Where does it mention about the 7.58lm.. I did not find it...


Um, the seventh line down, the one that states "Luminous flux: 7.58lm"... :fail:

Seriously, you're not listening to anyone, multi-thread spamming with pics that don't relate to anything, and it's increasingly looking like this is with regards to a commercial product you are trying to flog but are in an argument with the manufacturer as to it's rating.


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## Farhaj (May 4, 2014)

> Please stop.
> 
> You don't understand your question, and keep showing info that indicates you are not understanding your question.
> 
> ...





1) I want to use the Flash Light inside sea to see at night time .. that have enough intensity so that I can see in deep Under ground.. probably, with this is what happens is that when heavy waves comes we are unable to see till the end and gets distorted the light.. So, If I know all the data and details of this light; I won't have confusions in buying another one by seeing the specs and practiced practically..

2) You have claimed that their is no way to calculate Lumens from Candelas and so on.. but Why this Formula Mentioned here is not efficient or not suitable for calculation of Lumens for this White Straw Hat LED Flashlight.. or is it suitable..*If, not then for what purpose is it used...? **http://www.rapidtables.com/calc/ligh...calculator.htm*


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## Farhaj (May 4, 2014)

RoGuE_StreaK said:


> Um, the seventh line down, the one that states "Luminous flux: 7.58lm"... :fail:



That Picture which I posted was from Manufacturer.. they claim it to be 7.58 Lumens under thier tests.. not Me.. So, I am trying to come to a point how far it is true.. 
2) as I posted my recent picture; I already calculated,measured and shown some results on the Readings taken showing that some of it which they mention is true other some values are not.. and some needs to be found out..


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## TEEJ (May 4, 2014)

Farhaj said:


> 1) I want to use the Flash Light inside sea to see at night time .. that have enough intensity so that I can see in deep Under ground.. probably, with this is what happens is that when heavy waves comes we are unable to see till the end and gets distorted the light.. So, If I know all the data and details of this light; I won't have confusions in buying another one by seeing the specs and practiced practically..
> 
> 2) You have claimed that their is no way to calculate Lumens from Candelas and so on.. but Why this Formula Mentioned here is not efficient or not suitable for calculation of Lumens for this White Straw Hat LED Flashlight.. or is it suitable..*If, not then for what purpose is it used...? **http://www.rapidtables.com/calc/ligh...calculator.htm*





1) Seeing inside the sea at night time....seeing deep underground? 

When heavy waves come ?

This is VERY hard to understand.


Can you simplify the scenario, and simply say what you are doing, and trying to see?


I THINK you are describing being on a boat?

I can't tell if you are trying to see underwater (The beam is shining on something under the water), or, if you are trying to see past waves (The waves are in the way)?

I THINK the "Underground" is a mistranslation of "deep underwater"?

Is the flashlight IN the water (Submerged), or, in the air, shining down AT water, or, at an above water target that the waves obscure?




Are you trying to see deeper underwater, but, the waves distort the view?


If any (ANY) of the above is true, then the lumens you are asking about are not relevant, its actually the cd of the light that will be important.

Can you please describe where you are with the flashlight, and, what it is you are trying to see, and, how far away from you, in meters, the things you are trying to see, are?







2) Notice it says to enter the apex angle?

That is another data point, NOT just taking the candela and plugging it into a formula to get lumens.

THAT apex angle is the "way" that they are accounting for the DISTRIBUTION of light, essentially, the homogenization needed.

Do you KNOW the apex angle for the LED you HAVE the candela for?

If so, sure plug it in to that formula.


It will not be correct per se, but, it will be at least mathematically close for that specific part of the beam you specify at least. It will NOT be the lumens of the LED though.


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## Farhaj (May 4, 2014)

TEEJ said:


> 1) Seeing inside the sea at night time....seeing deep underground?
> 
> When heavy waves come ?
> 
> ...



*Please answer all the questions numerically. and orderly clearing and clarrifying each points...*


1) I am roaming Inside Sea water with my friend (s) and we are looking for sea species to ... the light is on our fore head and the water level; if it is upto our knees we can see thorugh the underwater sea to the ground level; or if the water is steady up to our thighs we can still see up till ground through that flashligt.. but the moment the waves form or the water level is high it causes distortion and we are unable to look till ground through the sea water.. .. 

2)also, the light is not dispersed into large area and we are afraid to go further in deep coz of the light focusing on small area and not big area and secondly also not clear to look through... I hope u understand what I mean.. 

3) so I was thinking either get a flashlight with *Higher Watts* could solve the problem coz I saw in the car the emergency light when lit on towards sea; it would through Light at a* long distance* and also on the closer areas towards light one is able to see through the underwater through this emergency light in the car.. then, I came to know that Cree has invented LEDs that can t*hrough more Lumens even at a lesser watts*.. so thought that *Lumens higher* are the basic thing.. coz I am thinking that even DP ( the same company has 3 Watts Flashlights as Well).. 

4) the Apex angle is mentioned in the data sheet here at http://underwaterseaplants.awardspace.com/led.pdf So if you input the values here at this Calculator *http://www.rapidtables.com/calc/ligh...calculator.htm *.. the answer is strange.. check it and let me know..

*Please answer all the questions numerically. and orderly clearing and clarrifying each points...*


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## TEEJ (May 4, 2014)

Farhaj said:


> *Please answer all the questions numerically. and orderly clearing and clarrifying each points...*
> 
> 
> 1) I am roaming Inside Sea water with my friend (s) and we are looking for sea species to ... the light is on our fore head and the water level; if it is upto our knees we can see thorugh the underwater sea to the ground level; or if the water is steady up to our thighs we can still see up till ground through that flashligt.. but the moment the waves form or the water level is high it causes distortion and we are unable to look till ground through the sea water.. ..
> ...





*You don't need lumens, that specification is not going to help you. (And apex angle is NOT supplied)
*
My understanding so far:


1) You are standing in water with a headlight, looking for things that live in the ocean. You are looking down at the water, and, can see to the bottom if the water is calm and flat, but, when a wave warps the surface, it distorts your view.

2) The light only shows you a small area at a time, and not well.

3) None of the things here are relevant....forget about them.

4) The apex angle is not provided, and even if it were, for your application, its not relevant...forget about it.



----------------------------

What you need is to put a FLASHLIGHT under water, and shine it at what you want to see. The light hitting the surface of the disturbed water is distorted and diffracted. Adding more intensity will not help to overcome that. 

The LED is not the answer, the reflector used to FORM THE BEAM from the LED is the answer.

The BEAM ANGLE of the flashlight, not the apex angle of the LED itself, is what will be important.

The deeper the bowl of the reflector, the better the light will penetrate depths...but, you need the light to be UNDER the water to get UNDER the waves.

Do you understand what I am saying?


If you do, the NEXT step is to maximize that penetration, with the cd of the resultant beam...but, first, I need you to focus on the above points and confirm that you understand.


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## Farhaj (May 5, 2014)

TEEJ said:


> *You don't need lumens, that specification is not going to help you. (And apex angle is NOT supplied)
> *
> My understanding so far:
> 
> ...



1) It says _50% Power Angle 2θ½ IF = 20mA --- 15 --- deg ;_ .. in the data sheet.. *is that not apex angle. to put in the table.. if it is not apex angle then what it is..
*
2) if the water level is still calm but if the water level is high; we are still not able to see the depth cause the light wont hit or beam wont show till the sea bed on a higher level of water; but my guess is a *higher lumens or watts or mcd light *can show till the sea bed as well... as you know we see these projection lights on outside many shops focusing on the sky; and we see it hitting till the clouds...

3) I did not get a much better idea of the _BEAM and the BEAM ANGLE of the Flash light_ to improve the VISION.. Also, about b_owl of the reflector, the better the light_


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## TEEJ (May 5, 2014)

Farhaj said:


> 1) It says _50% Power Angle 2θ½ IF = 20mA --- 15 --- deg ;_ .. in the data sheet.. *is that not apex angle. to put in the table.. if it is not apex angle then what it is..
> *
> 2) if the water level is still calm but if the water level is high; we are still not able to see the depth cause the light wont hit or beam wont show till the sea bed on a higher level of water; but my guess is a *higher lumens or watts or mcd light *can show till the sea bed as well... as you know we see these projection lights on outside many shops focusing on the sky; and we see it hitting till the clouds...
> 
> 3) I did not get a much better idea of the _BEAM and the BEAM ANGLE of the Flash light_ to improve the VISION.. Also, about b_owl of the reflector, the better the light_




1) The measurement is what it says it is, the Power Angle of 50% (What angle gave 50% power). The apex angle is needed to include the entire output of the LED (NOT just what's in 50% of the beam angle)

You'd need 100% (180º not 90º, etc) of what its emitting.

Also, it doesn't matter, because the LED's angle, and the angle that would matter when using it as a flashlight, are not related in this case...so drop it, its the wrong data set.


2) Higher lumens doesn't penetrate water (The sun's got a lot of lumens, and obviously is not working for you?) - A question not already addressed - Are you doing this at night, or, the day?

mcd is not relevant, as you need MANY MANY cd to penetrate the water, not fractions of a cd.

I find 30 k cd and up is good for penetrating water...say to about 3' or so depending on turbidity (Cloudiness, etc) A higher cd can penetrate deeper, and so forth.


You are looking at LED performance, but, its not translatable in this context. Again, you will (WILL) see better if you put the light under the water (The light is in your hand, you put it under the water (Its below the surface of the water, like a fish, pointed at the sea floor).

Putting the LIGHT under the water gets you around the problem of the light reflecting/being distorted, by the TOP of the water. 



3) The reflector bowl of the flashlight shapes the beam, and, you want a beam that is shaped so as to THROW the beam as far as you can, so it can reach the sea floor and show you what's down there.

A light BULB sends out light in all directions, a big round ball of light. A reflector bowl is used to focus that light, to make it all go in one direction. In YOUR context, you want that direction to be down to the sea floor, and not wasted on your buddy to your side, the sky, etc.


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## idleprocess (May 5, 2014)

Using the extremely rudimentary values in the linked PDF (10cd typical/20cd maximum, 15-degree half-angle), and generously assuming a consistent linear falloff from the center peak, a crude spreadsheet using 5-degree samples shows 2.8 - 5.6 lumens per LED.

10 cd typical:

```
LUMENS: 2.8128
° Ref  Steradian  cd       Lm/seg
-----  ---------  --       ------
0      0.0060     10.0000  0.0598
5      0.0478     8.3333   0.3981
10     0.0952     6.6667   0.6346
15     0.1419     5.0000   0.7093
20     0.1875     3.3333   0.6249
25     0.2317     1.6667   0.3861
30     0.2741     0.0000   0.0000
```

20 cd maximum:

```
LUMENS: 5.6256
° Ref  Steradian  cd       Lm/seg
-----  ---------  --       ------
0      0.0060     20.0000  0.1196
5      0.0478     16.6667  0.7962
10     0.0952     13.3333  1.2691
15     0.1419     10.0000  1.4187
20     0.1875     6.6667   1.2498
25     0.2317     3.3333   0.7722
30     0.2741     0.0000   0.0000
```

I searched a few geometry sites for sphere area formulas and had to re-learn trig in Excel, but it's not a terribly complex method. Here's the data for a 5-degree sampling method:

Angle,Steradian
0,0.0060
5,0.0478
10,0.0952
15,0.1419
20,0.1875
25,0.2317
30,0.2741
35,0.3144
40,0.3523
45,0.3876
50,0.4199
55,0.4490
60,0.4747
65,0.4968
70,0.5151
75,0.5295
80,0.5398
85,0.5461
90,0.5481
95,0.5461
100,0.5398
105,0.5295
110,0.5151
115,0.4968
120,0.4747
125,0.4490
130,0.4199
135,0.3876
140,0.3523
145,0.3144
150,0.2741
155,0.2317
160,0.1875
165,0.1419
170,0.0952
175,0.0478
180,0.0060

Copy the entire table into a text editor, save as a .csv file then open with a spreadsheet application such as Excel. For each *Angle* field, enter a candela (cd, or 1/1000th of the mili-candela or mcd values many LED manufacturers still use) then multiply times the value in the corresponding *Steradian* column to get lumens for that segment; sum all segment lumens to get total lumens.

Using 1 cd for all 37 segments yields 12.5664 lumens, which is the 4-digit approximation for 4*Pi, the number of steradians in a sphere, so it passes a basic sanity test.


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## Farhaj (May 6, 2014)

idleprocess said:


> Using the extremely rudimentary values in the linked PDF (10cd typical/20cd maximum, 15-degree half-angle), and generously assuming a consistent linear falloff from the center peak, a crude spreadsheet using 5-degree samples shows 2.8 - 5.6 lumens per LED.
> 
> 10 cd typical:
> 
> ...



Really, I could not understand that Part .. how you got the values.. can you please explain it with the forumilas you used.. or is it also realted to this calculation on the website or is it different..? http://www.rapidtables.com/calc/light/mcd-to-lumen-calculator.htm


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## TEEJ (May 6, 2014)

Farhaj said:


> Really, I could not understand that Part .. how you got the values.. can you please explain it with the forumilas you used.. or is it also realted to this calculation on the website or is it different..? http://www.rapidtables.com/calc/light/mcd-to-lumen-calculator.htm




Be aware that NONE OF THAT will answer your REAL question about what you are trying TO SEE UNDERWATER. The above LED are not the answer, period. Calculating the lumens from them is not the answer, period.



You are off on a tangent from where you need to go....and wasting a lot of time and resources.


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## Farhaj (May 6, 2014)

TEEJ said:


> 1) The measurement is what it says it is, the Power Angle of 50% (What angle gave 50% power). The apex angle is needed to include the entire output of the LED (NOT just what's in 50% of the beam angle)
> 
> You'd need 100% (180º not 90º, etc) of what its emitting.
> 
> ...




1) I am looking and searching sea walking in the Night with my freind..

2) If, I ask the Manufaturer to tell me the apex angle, can that help.. 

is the apex angle like this mentioned here " [h=4]Apex Angle[/h]Since the lumen and the candela measures are related through the viewing angle (or apex angle), it is useful to know how this angle is defined. One measures the angle between the axis where the light source gives its highest luminous intensity and the axis where that intensity is reduced to 50%. In the picture at the right, this angle is denoted with θ. The apex angle is twice that angle (meaning 2θ). 

Observe that the reduction of intensity to 50% is based on a linear scale, but that our perception of brightness is not linear. The CIE has standardized the relation between luminous intensity and perceived brightness as a cubic root; other sources claim that a square root better approximates this relation. See also the page on colour metric. 

The three-dimensional angular span for an apex angle, using Ω for the angular span (in steradian) and 2θ for the apex angle, is:""

in this link: http://www.lightart.com.tr/useful_information.php

3) at the end of that page it says that ""Another complexity is that the values for candela, lumen and lux are standardized for light with a wave length of 555 nm, or green light. For LEDs of a different colour, a weighting function should be applied, usin_g a standardized model of the human eye."""
_What does that supposse to mean..?_
_


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## TEEJ (May 6, 2014)

Farhaj said:


> 1) I am looking and searching sea walking in the Night with my freind..
> 
> 2) If, I ask the Manufaturer to tell me the apex angle, can that help..
> 
> ...



It WON'T help, because you are looking at the wrong things.

Its like you are hungry, and walk into a grocery store, and say you want to eat something because you're hungry.....and see a rack of plastic toys. You know that plastic is made of carbon compounds, and you want hydrocarbons to eat. But, the toys are made of PETROLEUM HYDROCARBONS.

You then start asking how to CONVERT the petroleum hydrocarbons into regular hydrocarbons, so you will know how many toys to eat.


The clerks says, the toys are not the best choice to eat, perhaps the rack of bread would be a better place to get hydrocarbons to eat?

And you say, just tell me how to calculate how many toys to eat....here's a chart showing the petroleum hydrocarbon content of various plastics.


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## Farhaj (May 6, 2014)

TEEJ said:


> It WON'T help, because you are looking at the wrong things.
> 
> Its like you are hungry, and walk into a grocery store, and say you want to eat something because you're hungry.....and see a rack of plastic toys. You know that plastic is made of carbon compounds, and you want hydrocarbons to eat. But, the toys are made of PETROLEUM HYDROCARBONS.
> 
> ...




Hahaha
I still could not get the full idea of it.. can You be little proper in answering the last post.. I know you get irritated but still helping is good.!


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## TEEJ (May 6, 2014)

Farhaj said:


> Hahaha
> I still could not get the full idea of it.. can You be little proper in answering the last post.. I know you get irritated but still helping is good.!



LOL

I'm TRYING to steer you to the BREAD!!!!! (BUT you keep asking how many toys to eat!!!)


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## Farhaj (May 6, 2014)

TEEJ said:


> LOL
> 
> I'm TRYING to steer you to the BREAD!!!!! (BUT you keep asking how many toys to eat!!!)



Please, can you once again steer me to the Bread.. xplain it like you do a small child... step by step... with answers to the questions thats pops in my mind after the xplainations..


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## TEEJ (May 6, 2014)

Farhaj said:


> Please, can you once again steer me to the Bread.. xplain it like you do a small child... step by step... with answers to the questions thats pops in my mind after the xplainations..



OK, forget ALL about the LED chart. NOTHING there is relevant to your quest.

OK?


Get a waterproof flashlight rated at 30 k cd or more (30 k cd is good for ~ 2-3' of water)...hold the flashlight under the water pointed at what you want to see, see it. 

That's it.



If you want to see through deeper water, get more than 30,000 cd, with about double the cd to see about 25% deeper. If the water is cloudy, the particles in the water will reflect back light, making a "Fog" that's hard to see through, with any light.

If you add a face mask, and put your face under water, you will see even better under water.



*NOTE: DO NOT CONFUSE the mcd of the LED itself with the cd of the FLASHLIGHT, ignore the LED specifications....its the FLASHLIGHT specifications you need to look at.

*


You did not say before, but, are you doing this at night, or, during the day?


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## Farhaj (May 6, 2014)

TEEJ said:


> OK, forget ALL about the LED chart. NOTHING there is relevant to your quest.
> 
> OK?
> 
> ...



I told you at night.. during day it is clear to see till the sea bed.. and What do Lumens, CD and Watts account for in a flashlight.. can you detail each one properly..


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## TEEJ (May 6, 2014)

Farhaj said:


> I told you at night.. during day it is clear to see till the sea bed.. and What do Lumens, CD and Watts account for in a flashlight.. can you detail each one properly..



Lumens is telling you the total output.

You can't SEE lumens though.

cd is the candela, which is the lux at one meter (Back calculated to one meter as a standard)

Watts for an LED flashlight spec is not meaningful in your context, its used more for incandescent bulbs. 


When a flashlight emits lumens (Photons), what you CAN see is when they HIT SOMETHING, and bounce back to your eye. THEN you see "lux", or brightness from the object reflecting the light back to your eye.

The light on the ground with a full moon is about 0.25 - 0.3 lux, if that helps to get a feel for what a lux looks like.


The cd of a flashlight TELLS YOU how far the beam can be projected to a particular lux (in air, not water though), or what the lux would be at a particular range.

The higher the light's cd, the better it is at projecting the beam a long distance. It will project farther in air than water, but, it is proportional, in that the farther it can project in air, the farther it can project in water.

Sea water is a lot harder to see THROUGH, because it tends to have STUFF in it...like clouds of debris, etc...and water itself is harder to get light to penetrate through, as the light is diffracted, diffused, etc.


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## Farhaj (May 6, 2014)

TEEJ said:


> Lumens is telling you the total output.
> 
> You can't SEE lumens though.
> 
> ...



Then why are majority of Flashlights are mentioing We have High Lumens power in this so and so flash light.. Also, Cree mentions that they have LEDs that have like 300 + lumens per LED for only 1 watt supply... also, how do u define lux..


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## TEEJ (May 6, 2014)

Farhaj said:


> Then why are majority of Flashlights are mentioing We have High Lumens power in this so and so flash light.. Also, Cree mentions that they have LEDs that have like 300 + lumens per LED for only 1 watt supply... also, how do u define lux..




Because ADVERTISING is focused on what SELLS things, and, they LIE to you so you buy their stuff.



CREE makes LED that can put out over 1500 L, at higher drive levels (Forget the watts, again, not the most useful for LED).


Lux = lumens/square meter.

cd = lux at one meter of range



As lux = lumens/square meter, that means that the same lumens, in a smaller area = higher lux. If spread out more, the same lumens in a larger area = lower lux.


Make sense?



So, a light with a high lumen number is making more TOTAL light....but, it might be spread out, as from a light bulb, or, tightly focused like a laser beam.

The more tightly its focused, the higher the lux CAN be...for a given number of lumens.


If you want to know how FAR a beam can be used at, you use the cd to calculate it.


The light's intensity drops according to the inverse square law, so, at double the distance, its FOUR times dimmer, or, at HALF the distance, its FOUR TIMES brighter, etc.


If you know the cd (lux at one meter), you can use the inverse square law to calculate the lux at any other distance.

This is not going to be accurate in ocean water though due to a lot of variables, but, its PROPORTIONAL, in that higher cd goes farther in water too.


A light's lux at one meter is measured at the brightest part of its hot spot...so, it ONLY represents how far THAT PART of the beam can go. The OTHER parts of the beam will not go as far.


That is one of the reasons WHY knowing the lux or cd can't be used to find the lumens, as its not a measurement of the WHOLE beam, just the brightest part.


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## Farhaj (May 6, 2014)

TEEJ said:


> Because ADVERTISING is focused on what SELLS things, and, they LIE to you so you buy their stuff.
> 
> 
> 
> ...




1) so, companies claiming higher lumens on their box covers falsifies the fact that they will through more intensified light in water.. Or like these DP company states that they have higher watts flash light like 20 Watts flash light claiming more light and at more further beams..

2) so, what needs to be looked is cd or mcd of the leds in the flash light and at what amperes is it operating for the mentioned cd as in the datasheet.


3) see, as in these images.. Higher watts higher lights and so on..


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## idleprocess (May 6, 2014)

Farhaj said:


> Really, I could not understand that Part .. how you got the values.. can you please explain it with the forumilas you used.. or is it also realted to this calculation on the website or is it different..? http://www.rapidtables.com/calc/light/mcd-to-lumen-calculator.htm



As TEEJ has mentioned, this doesn't address your issues - I did this as an exercise largely for my own edification and to improve on a lengthier method I recall working on some years ago that was decidedly less efficient. The Rapid Tables calculator uses some other method since it does not look at intensity by section and we know that our light source has variable intensity within its beam profile; I do not recall the calculation, but I recall something similar that worked best for narrow beams with increasing error as the beam widened.

Essentially, I built a table with the reference angles _and_ the half-angles between them. In order to find my X-coefficient I took the sin of angle; the Y-coefficient was found by taking the cos of the angle. For each reference angle (except for 0 and 180), I subtracted the adjacent half-angle Y-intercepts to find the height. Using the height values, I determined the area of each section: _2 * Pi * r² * h_. The cap areas (0 and 180 degrees) require a different formula: _Pi * ( SQRT(h * (2-h) )² + h²)_; cap height is determined by subtracting the 2.5 (or 177.5) degree Y-coefficient from 1 (our radius, for simplicity's sake).

I've slept a few times since I built this thing; I would advise checking some geometry sites to be certain of the calculations if you're really interested in approximating lumens from uniform cylindrical LED's.


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## TEEJ (May 7, 2014)

Farhaj said:


> 1) so, companies claiming higher lumens on their box covers falsifies the fact that they will through more intensified light in water.. Or like these DP company states that they have higher watts flash light like 20 Watts flash light claiming more light and at more further beams..
> 
> 2) so, what needs to be looked is cd or mcd of the leds in the flash light and at what amperes is it operating for the mentioned cd as in the datasheet.
> 
> ...





You want a FLASHLIGHT, not a head lamp....so you can hold it under the water pointing at the sea bed.


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## Farhaj (May 7, 2014)

TEEJ said:


> You want a FLASHLIGHT, not a head lamp....so you can hold it under the water pointing at the sea bed.



1) No, sorry to say you were mistaken.. I have to get a flash light coz I have stuff with me in hands when in sea water.. so it has to be a head flashlight,,

2) so, companies claiming higher lumens on their box covers falsifies the fact that they will through more intensified light in water.. Or like these DP company states that they have higher watts flash light like 20 Watts flash light claiming more light and at more further beams..

3) so, what needs to be looked is cd or mcd of the leds in the flash light and at what amperes is it operating for the mentioned cd as in the datasheet.


4)see, as in these images.. Higher watts higher lights and so on..


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## Farhaj (May 7, 2014)

idleprocess said:


> As TEEJ has mentioned, this doesn't address your issues - I did this as an exercise largely for my own edification and to improve on a lengthier method I recall working on some years ago that was decidedly less efficient. The Rapid Tables calculator uses some other method since it does not look at intensity by section and we know that our light source has variable intensity within its beam profile; I do not recall the calculation, but I recall something similar that worked best for narrow beams with increasing error as the beam widened.
> 
> Essentially, I built a table with the reference angles _and_ the half-angles between them. In order to find my X-coefficient I took the sin of angle; the Y-coefficient was found by taking the cos of the angle. For each reference angle (except for 0 and 180), I subtracted the adjacent half-angle Y-intercepts to find the height. Using the height values, I determined the area of each section: _2 * Pi * r² * h_. The cap areas (0 and 180 degrees) require a different formula: _Pi * ( SQRT(h * (2-h) )² + h²)_; cap height is determined by subtracting the 2.5 (or 177.5) degree Y-coefficient from 1 (our radius, for simplicity's sake).
> 
> I've slept a few times since I built this thing; I would advise checking some geometry sites to be certain of the calculations if you're really interested in approximating lumens from uniform cylindrical LED's.



Thanks for the explaination.. still have confusions in understanding and figuring out this.. can you show some website link or details from where you got this info... and also you say that our light is not linear so something like this would more of be an approximation to the true lumens..?


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## TEEJ (May 7, 2014)

Farhaj said:


> Thanks for the explaination.. still have confusions in understanding and figuring out this.. can you show some website link or details from where you got this info... and also you say that our light is not linear so something like this would more of be an approximation to the true lumens..?



The issue is complicated because you are confusing the LED lumens and mcd with the LIGHT's lumens and cd.

Essentially, the emissions are not uniform, and, measurements of the performance at one POINT in the emission may not represent what you'd measure at ANOTHER point, etc....as it they are NEVER representative except by luck/coincidence.

So, if you TRY to take a published specification for an LED, for mcd....that's ALL you know about it. mcd is measured ONLY at ONE point, the brightest point....not anywhere else. So, the REST of what the LED is making is LESS BRIGHT.



As for head lamp vs flashlight....the question to ask is, if its more important to SEE, or, to have the hands free? If hands free is more important, then no matter what you get, the light will hit the surface of the water, and, will be distorted, making it hard to see (The entire reason you came here for advice).


Plan B - Put the light THROUGH a float, so its pointed into the water, but you don't have to "hold it".

Plan C - STRAP the head light or flashlight onto your wrist/arm...so when you reach down, the light is pointed underwater.


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## Farhaj (May 7, 2014)

TEEJ said:


> The issue is complicated because you are confusing the LED lumens and mcd with the LIGHT's lumens and cd.
> 
> Essentially, the emissions are not uniform, and, measurements of the performance at one POINT in the emission may not represent what you'd measure at ANOTHER point, etc....as it they are NEVER representative except by luck/coincidence.
> 
> ...



1) Reply to my previous post as well..

2) we have fishing stuff in our hand and that is the most important and secondly the light has to be on the fore head coz where ver we turn the light showas at that angle and no other alternative..


3) u say mcd is at focusing on one point and Lumens is pointing on all the other points..? and that rapid table forumla is valid or could be valid only for light focusing on one point..

4) How are these lights then different with respect to watts then.. do they have good intensity to through or how..


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## TEEJ (May 7, 2014)

Farhaj said:


> 1) Reply to my previous post as well..
> 
> 2) we have fishing stuff in our hand and that is the most important and secondly the light has to be on the fore head coz where ver we turn the light showas at that angle and no other alternative..
> 
> ...





There is no correlation, or, way to tell.

You are comparing a head light with no specs other than watts to LEDs...apples and oranges, not apples and apples.



Its like being told the miles per gallon for a car, and wanting to know how fast it can go based on that.


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## Farhaj (May 7, 2014)

TEEJ said:


> There is no correlation, or, way to tell.
> 
> You are comparing a head light with no specs other than watts to LEDs...apples and oranges, not apples and apples.
> 
> ...



What about the reaminign things I asked,,,


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## TEEJ (May 7, 2014)

Farhaj said:


> What about the reaminign things I asked,,,



I didn't see anything that was relevant....

If there's something related to seeing into the water, say it again, I must have missed it.


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## Farhaj (May 7, 2014)

TEEJ said:


> I didn't see anything that was relevant....
> 
> If there's something related to seeing into the water, say it again, I must have missed it.



Well, these parts..:

2) we have fishing stuff in our hand and that is the most important and secondly the light has to be on the fore head coz where ver we turn the light showas at that angle and no other alternative..


3) u say mcd is at focusing on one point and Lumens is pointing on all the other points..? and that rapid table forumla is valid or could be valid only for light focusing on one point..

4) WE are doing it in the night.. U know with this Light we are Ablee to see in low waters (the same wave as in hihgher levels if formed in low waters; we are still able to see)... but that wont happen in higher levels..


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## TEEJ (May 7, 2014)

Farhaj said:


> Well, these parts..:
> 
> 2) we have fishing stuff in our hand and that is the most important and secondly the light has to be on the fore head coz where ver we turn the light showas at that angle and no other alternative..
> 
> ...





2) Then the light will hit the surface of the water and be distorted and you won't see well, which is the problem you came to find a solution for...unless the water is calm and flat.


3) MEASUREMENT is at one point, NOT the focus. That's why the SPECIFICATIONS don't work for your use. And - mcd of LED and cd of the light, are not comparable for your use.


4) To see in DEEPER water, you need a flashlight with a higher cd (NOT an LED with higher mcd). The mcd of the LED is not related to the cd of the light in the way that you want it to be.


If you strap the light to your wrist or arm, etc...so it can be under water, you could still use your hands to hold things, but also aim the light where your arm points...could you do that?


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## RoGuE_StreaK (May 7, 2014)

Strap lights to your knees/shins?

There's a whole sub-forum on dive lights here, I'm sure you'd find people with knowledge specific to your problem there.


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## Farhaj (May 8, 2014)

TEEJ said:


> 2) Then the light will hit the surface of the water and be distorted and you won't see well, which is the problem you came to find a solution for...unless the water is calm and flat.
> 
> 
> 3) MEASUREMENT is at one point, NOT the focus. That's why the SPECIFICATIONS don't work for your use. And - mcd of LED and cd of the light, are not comparable for your use.
> ...




tieing lights to the arms is a bit complicated.. really coz we hit here and there in water as well with arms on sea creatures so not worthy..


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## Farhaj (May 11, 2014)

Strapping the light is not helpful


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