Beginner's Guide to explain simple LED flashlight.

[doceric]

Thanks! This is really helpful for beginners like me..

 

[siwasher]

OK, now understand that I'm a true beginner, with little understanding of technical issues. That said, I have two problems with the following quote from the original post. I'll overlook the first as a mere typo, but the second I truly don't understand:

"...life spin is much longer too. The brightness of newer Led will increase ~30% per year."

INCREASE? How long until it's brighter than the sun?

 

[download]

Thanks for reminding. Is it better like that?

The efficiency or brightness of Led will be improved ~30% every year.

 

[Blglover96]

Nice


Sent from my iPhone using Tapatalk - now Free

 

[Tikiman]

Great Beginner's Guide
thanks..

 

[enzo thecat]

This might be a stupid question but the heatsink reminded me to ask. Why do our LED flashlights emit so much heat. I thought LEDs were supposed to run cool. In fact the 100 watt bulbs I have installed in my ceiling can light fixtures are completely cool to the touch. Why such a difference between applications.

 

[download]

Fluorescent lamp and LED (Light-emitting diode) are different technology, just like gasoline engine car and pure electric car.
The outlook are similar but they use two different kind of technology inside.

For more technical details, please see:
http://en.wikipedia.org/wiki/Light-emitting_diode#Physics

 

[enzo thecat]

Fluorescent lamp and LED (Light-emitting diode) are different technology, just like gasoline engine car and pure electric car.
The outlook are similar but they use two different kind of technology inside.

For more technical details, please see:
http://en.wikipedia.org/wiki/Light-emitting_diode#Physics

How did fluorescents enter into the discussion?

 

[download]

Sorry enzo thecat, misunderstood your 100 watt bulbs was Fluorescent lamp.

Heat is side product when the led is driven by more current.
Lower current = Higher Efficacy, >0.3A will generate more light per current.
Higher current = Lower Efficacy, <1A will generate less light per current and more heat.

eg.1 Led Christmas tree lighting, the loading of led is ~0.05A, cool to touch, right?
eg.2 Cree XML, when the current load is 0.05A, it will be cool to touch too.
When the current load reach 3A, it will generate a lot of heat, it will kill itself without suitable heatsink.

 

[jamie.91]

What a good thread!

 

[mikemild13]

Thanks for this post. If no one minds, I would like to use the diagrams to teach my young'ns. I understand the technology but can't explain it worth a darn.

 

[download]

We like to share what we learn from here.

 

[mikemild13]

We like to share what we learn from here.

I appreciate all of the knowledge shared here. A lot of the info is over my head but I read it anyway. This post breaks it down to the basic level which makes it a great tool for beginners.

 

[dklinko3]

Thanks for this, it will help me a lot in deciding which flashlight to buy as my very first high quality LED light!

 

[KARADENIZ]

nice thread , thank
is there any comparison chart of pwm boards to their efficiency?

 

[download]

AMC7135 board
http://www.candlepowerforums.com/vb/newreply.php?do=newreply&p=2405842

1050mA version:

1400mA version:

Pretty good boards, as long as your in they're small voltage range. DX recommends that you stay within 3.6V to 4.5V. I read that is because between 4.6V to 6.0V (which it can take up to 6.0V) it gets very hot. In my testing I used a small fan to keep the board cool so this did not affect me.

These are a great alternative to resistors, even though resistors are cheaper. The best thing to do here is order 20 of the 1400mA version and you can remove each of the black AMC boards and each one you remove will cut down the output current by 350mA. I tested this and it does work.

Where these boards beat resistors is that these give you a semi-regulated output. If you use resistors and alkalines (for example) the flashlight will never be brighter than when you first fire it up. After that, the batteries will start to dim. If you chose your resistor based on the fresh battery voltage, as the batteries start to drain, your output will drop. With these, as long as your voltage stays above about 4.0V you get the full output. The 700mA version should need a lower voltage and the 350mA an even lower voltage. So that semi-regulation is worth the extra money to me. I can't tell you how much time and headache direct drive / resistors / alkalines have caused me.

I definitely love a good boost/buck convertor more than these, but these things are not bad little boards. I thought others could benefit from these numbers.

 

[bitnick]

The efficiency or brightness of Led will be improved ~30% every year.

Well... not quite.

(The source for the below is Do The Math, an IMO extremely interesting blog that looks at energy and physics from a mathematical perspective. Well worth a read!

The units used below are the lumen [lm], watt [W], and nanometer [nm].)

The theoretical maximal luminous efficacy for any light source, regardless of technology, is 683 lm/W. This would be a monocromatic source emitting at 555 nm ("laser green"), and it would not get warm, no matter how bright it was or how much power it used, since all the supplied power would be converted into useful photons and "beamed away".

For a white light, the theoretical maximal efficacy is lower, since the sensitivity of our eyes gets lower the farther from 555 nm we come, and white light is a mixture of wavelengths between ca 450 nm (blue) and 660 nm (red).

To make a long story short (see the link above for details), a white light source with "ideal efficacy" and a color temperature of 5800 K could reach 310 lm/W maximum (and would have a CRI of 94). At 2800 K, we could reach 370 lm/W (and the CRI would be 87). Again, these would not even get warm, regardless of brightness, since they are 100 % efficient.


Let's look at a modern LED - the Luxeon T. At a reasonable CRI of >80, and a "typical" current of 700 mA, it has a luminous efficacy of around 100 lm/W. That's not that far away from the theoretical maximum!

In fact, at 30 % improvement per year, we would hit the theoretical maximum in only 5 years! 100 [lm] * 1,30^5 = 371 lm!

It's pretty amazing really that we have light sources today whose efficacy can only be doubled twice before we hit the absolute theoretical maximum, regardless of technology!

 

[KARADENIZ]

@download,

thats what I was searching for, thanks

 

[download]

bitnick,

Thank for the good article, we will learn something about it. :twothumbs
It is my roughly estimation only for beginner understand the concept.

KARADENIZ, :thumbsup:

dklinko3 & minos2013, :welcome:

 

[lane478]

Thank you Download. That answered about a hundred questions I had all at once. I wish there were more threads to guide newbs learning to build and mod.