# LED Flux Spreadsheet: MC-E, P7, XR-E, XP-E, P4!



## Daekar (Feb 14, 2009)

I wanted to see what kind of output we were really going to get out of an MC-E at different drive levels so I made a spreadsheet. I used this page to help me reduce the graphs from the datasheet into equations. The equations are not perfect because I was eyeballing the lines on the graphs to derive data points, but they're pretty close. However, they may not be very good for extrapolating beyond the range of values shown in the datasheet graphs.

The spreadsheet calculates Vf, Tj, Nominal Flux, Actual Flux, and estimates OTF lumens based on 85% secondary optical efficiency and 98% anti-reflective window. It also has a simple bit that uses theoretical driver efficiency to give Lum/watt estimations - this does not scale automatically, so you must enter the correct efficiency value for the drive level selected. Use 100% driver efficiency for direct-drive applications. 

Please let me know what you think, and please point out any errors you might find!:candle:


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## Blindasabat (Feb 17, 2009)

*Re: Cree MC-E Spreadsheet! Bin, Vf, Tj, etc.*

Nice job! Thanks for the tool.

I just modified it to graph out the results of a wide spread of Amps.
I plan to also modify it to show Lumens over time as a battery runs down by taking data from the battery-Amp/time curves in the battery comparison tests in the Battery/Electronics forum.


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## Daekar (Feb 18, 2009)

*Re: Cree MC-E Spreadsheet! Bin, Vf, Tj, etc.*

Can you give us a link to your version? I would love to see what you've done, that sounds _very_ useful. I suppose it wouldn't hurt to add parallel calculations for P7, XR-E, XP-E, GDP, etc. Maybe I'll try to add that later this week (if my flashlight parts don't come, of course!)


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## Blindasabat (Feb 18, 2009)

*Re: Cree MC-E Spreadsheet! Bin, Vf, Tj, etc.*

I will have to post it to Google Docs (can't access from where I am) or something since I don't have my own web page. Why don't you PM me your email in the mean time, and I will send it to you.

The battery run-down I made a separate tab that you can fiddle with to duplicate any battery discharge curves you have or download from the battery comparison threads. I eyed mine up to act like 2x18650 driving an MC-E. You can see that the graph looks like a discharge curve, it estimates lumens at each 10-minute mark, then adds up cumulative mA-hr used at each 10 minutes to check against your battery capacity.


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## Daekar (Feb 18, 2009)

*Re: Cree MC-E Spreadsheet! Bin, Vf, Tj, etc.*

Thanks for sending me your file, that looks great!
I've been adding to the original file, so that it now does calculations for MC-E, P7, XR-E, XP-E, and P4. Interesting to see the differences side-by-side. The new file is here.


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## ledstein (Feb 20, 2009)

This sheet has one flaw, it only shows max and min luminous flux, not typical. 

You can also use this website for comparing high power leds: http://www.ledrise.com/index.php?cat=c2_High-Power-LEDs.html

Its not perfect but its all i could find.


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## Daekar (Feb 20, 2009)

ledstein said:


> This sheet has one flaw, it only shows max and min luminous flux, not typical.
> 
> You can also use this website for comparing high power leds: http://www.ledrise.com/index.php?cat=c2_High-Power-LEDs.html
> 
> Its not perfect but its all i could find.


 
:thinking: I'm confused... as I understand it, "typical" is a term used for the output of an entire part line, like all cool white XR-Es. However, the flux binning narrows things down to be more specific than "typical"... I could add a row that would show the average of max and minimum flux expected within a given bin... would that be helpful? :candle:


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## ledstein (Mar 2, 2009)

Typical usually shows an average of the lighting interval. 
The bin is a code for a lighting interval. 

I took a closer look at the datasheets and the one thing that all the producers (Cree, Lumileds, Seoul) have in common is the use of the min value. Cree doesnt use typical at all but has narrow min-max intervals, luxeon k2 has min and typical values but the typical value is not the min/max average at all and seoul p4 has the min and tyipical value but not the max (for rank U). 

So for the sake of using comparable data just stick with the min value.


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## Illum (Mar 2, 2009)

suscribed
good job:thumbsup:


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## Daekar (Mar 21, 2009)

New version of the spreadsheet! Got some revised equations which should make things a bit more accurate. Still have a few more equations to go, but this is most of them. A few other small changes made too.

New spreadsheet is here.


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## KuKu427 (May 15, 2009)

Very useful! Thank you very much!


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## Blindasabat (May 18, 2009)

Nice updates Daekar.


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## Justin Case (May 19, 2009)

This spreadsheet is very useful. I use it a lot. Saves me the hassle of going to the datasheets and using pencil and ruler to interpolate values all the time.

I've found some minor "bugs" in the spreadsheet:

- SSC P4 U flux bin is missing in cells F6 and F7
- Forward currents greater than the max (e.g., above 1000mA for a P4, above 700ma for an MC-E) result in erroneous calculations for Vf. This affects all subsequent cell calculations that depend on Vf (e.g., power, efficiency)
- Since Vf is specified as a low/high bin, the calculated Vf also should be given as such
- SSC P4 Vf for H voltage bin should be exactly 3V (as currently implemented by the spreadsheet). Cell F8 gives Vf as 3.00002325V.


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## Daekar (May 19, 2009)

Justin Case said:


> This spreadsheet is very useful. I use it a lot. Saves me the hassle of going to the datasheets and using pencil and ruler to interpolate values all the time.
> 
> I've found some minor "bugs" in the spreadsheet:


Justin: I'm glad you've found the spreadsheet useful! Thanks for the attention to detail in your comments, as well. Let me address each issue separately - 



Justin Case said:


> - SSC P4 U flux bin is missing in cells F6 and F7


There are now two sub-bins of the "U" bin, designated U1 and U2. The spreadsheet reflects this. Unless, of course, I have missed something and there still is a "U" bin lower than U1. I'll have to check the datasheets again.


Justin Case said:


> - Forward currents greater than the max (e.g., above 1000mA for a P4, above 700ma for an MC-E) result in erroneous calculations for Vf. This affects all subsequent cell calculations that depend on Vf (e.g., power, efficiency)


You are absolutely right. The equations derived from the datasheet equations are valid only for the range of values illustrated in the datasheet. Because of the nature of the polynomial equations the spreadsheet uses, sometimes even a small deviation outside the rated current for each emitter can cause very large inaccuracies. If I had specific test data to use in revising the equations further, this might be remedied, but a statistically significant sampling of parts would be necessary to derive those data points. I'm not aware of a place where I can find this information, so unless something changes, I'm afraid things will have to stand as they are.  


Justin Case said:


> - Since Vf is specified as a low/high bin, the calculated Vf also should be given as such


Good point! :thumbsup: I will try to incorporate that into the next revision.


Justin Case said:


> - SSC P4 Vf for H voltage bin should be exactly 3V (as currently implemented by the spreadsheet). Cell F8 gives Vf as 3.00002325V.


Right again. Because the equations are not exactly perfect, you will find small deviations like that throughout the spreadsheet. I would love for it to be otherwise, but I'm not sure how to achieve that. If anyone has any suggestions how to improve the conformance of the equations to the datapoints, I would LOVE to hear them, since they would be useful not only in this application, but in any place where I might use equations to model existing data. In particular, suggestions on how to improve accuracy of the equations for points outside the recommended maximum drive levels would be very welcome!


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## Justin Case (May 21, 2009)

Before there were the U1 and U2 sub-bins, there was just the U-bin. Even now, there are vendors who advertise the SSC P4 in just the U-bin.

Extrapolation capability would be nice. People do overdrive things, for example driving a Cree R2 beyond 1.0A.


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## spencer (May 22, 2009)

It is possible they still have old stock from before the bin split. It is not possible for them to determine if they are U1 or U2 if they were sold to them as just U bin. If it is just a straight U bin then it is likely the reel is a mixture of both U bins.


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## Justin Case (Jun 1, 2009)

Another issue is that when you enter 350mA forward current per core, as an example, you don't get the min and max rated lumens in rows 14 and 15. For a Seoul P4 U2 bin, I get 101.799 lumens min and 120.632 lumens max, instead of 100 and 118.5, respectively. Same with MC-E and SC P7. I didn't check the Cree XR-E and XP-E.

If the curve fitting is via polynomial fit, then you can always pass a unique polynomial eqn of degree n through n+1 data points with unique abscissae. For the first polynomial interpolation for row 14, one of those data points ought to be (350mA, 100lumens). For the second polynomial for row 15, one of those given data points should be (350mA, 118.5lumens).


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## Curt R (Jun 20, 2009)

This thread is very important and useful, the data obtained from and used in new flashlight design is a tremendous help. Perfections in the equations are not required as the output of the LEDs are not perfect or consistant. The fundimental references between the LEDs is importaint and that is why this program is so useful.

It would be a great help to CPFers if this thread were put into a sticky such as in the Flashlight Reviews forum, (Threads of Interest). 

I know that it would be a large undertaking to make a major change or addition to the program that Daekar worked on, but I am selfish and do not have the necessary skills to do what he has accomplished. Currently all types of LEDs are grouped together. I would like to see this broken up into three distinct programs rather than one very large program. Group one would be with the very high powered four die units such as the MC-E/P7/Ostar LEDs. Group two the K2-tffc/P4/XR-E types. And group 3 the new small XP-E/Z1/Rebel size. I would not even consider all available LEDs on the market, only thoes that lend themselves to new flashlight construction. 

As an incentive to take on the additional work I would like to make an offer of maybe a couple of new Peak Rebel Eigers or a Peak P7 Night Patrol.

Curt


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## Justin Case (Jun 21, 2009)

Curt R said:


> This thread is very important and useful, the data obtained from and used in new flashlight design is a tremendous help. Perfections in the equations are not required as the output of the LEDs are not perfect or consistant. The fundimental references between the LEDs is importaint and that is why this program is so useful.
> 
> It would be a great help to CPFers if this thread were put into a sticky such as in the Flashlight Reviews forum, (Threads of Interest).
> 
> ...



The issue isn't one of perfection. Rather it is one of confidence that the numbers are reasonably correct. There are known values for variables such as Vf and luminous flux at various given values for If. Thus, the calculations ought to reflect that. One can always use a tool as a black box, but it would be wise to know the accuracy limits of the numbers you get. Certainly, for many of the calculations I've made, the spreadsheet agrees quite well with my numbers (whether calculated or measured). But the Vf calculations, for example, seem to have the greatest deviation from measured data.

To do what you propose, you just need to do more curve-fitting of the data that is commonly available in the datasheets for the LEDs of interest.


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## MorePower (Jun 22, 2009)

Justin Case said:


> Another issue is that when you enter 350mA forward current per core, as an example, you don't get the min and max rated lumens in rows 14 and 15. For a Seoul P4 U2 bin, I get 101.799 lumens min and 120.632 lumens max, instead of 100 and 118.5, respectively. Same with MC-E and SC P7. I didn't check the Cree XR-E and XP-E.



The sheet is off by 2 lumens and that's not close enough? If you need that kind of precision, you ought to drop some serious cash on an integrating sphere and a nice current controlled power supply and test all your LEDs by hand.

When would the difference between 101.799 and 100 lumens ever matter?


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## Justin Case (Jun 23, 2009)

The lumens differences at 350mA don't matter. But Vf differences at say 1000mA can matter. And do you know what the lumens differences are at other drive currents? Maybe those differences don't matter either. But if you don't know what the differences are, you can't decide whether or not it matters.

Did you even know about these minor deltas before I mentioned them, or did you use the tool as a black box?


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## Curt R (Jun 23, 2009)

I build hundreds of flashlights using many different LEDs and different brands of LEDs. From my testing it does not matter which brand or type of LED I test the results are always the same. When using a bench power supply, LEDs from the same reel of 250 or 500 LEDs that are binned the same have very different characteristics within that reel. Some have high Vf, some low; some have higher or lower mA draws as compaired to the same Vf and there is no correlation between Vf and mA and Lumen output. I have had Lux III LEDs that had the same output as a P4 U bin even with a suposedly 35 Lumen, (50%), output difference. In a listed bin of 30% Lumen output from the low to the high as in the entire Seoul P4 U bin, there may be a total of a real world difference of 51% accoring to Henry's White Paper that he published a few years back. That also is the same for Cree, Nichia, and Lumileds. In tighter bin spreads there will of course be less overall per-cent changes from low to high outputs, but the spread is still greater than advertised. Why do I test the LEDs before assembley, I have a bunch that I consider unusable for my customers. 

When the manufacturer test the LED it is done at the rated current and then separated into the individual bins. The test procedure takes 20 to 25 milliseconds so as to limit junction temperature below 25 degrees C. The bins may include three different voltage levels, three different output levels and 12 to 15 different color tints. Then there is the tolerance of the output added onto the stated output bin level of typically + 5%. That increases or decreases the light output of the LED beyond what the manufacturers stated bin numbers are suppose to be.

The biggest variable is the individuals eye response. Each person has a dominate eye that sees color tint and intensity different from the other one. Also there is a requirement to double the light output needed of persons over the age of about 35 for every 13 year increase over that age to see the same degree of detail at night as 13 years previously. 

That is the reason when I stated that total precision in the formulas is not required. These varied results with LEDs are then compounded with the variations with the elctronic drive systems and the optics and the location of the LED within the optics themselves. Then we come to the batteries which then compounds the previous results even further. Not to mention, (which I will because it is generally overlooked), the non-visable corrosion build up on the contact surfaces of both the batteries and the flashlight contact points. That is why we use Gold plated contacts on our flashlights. We have observed an increase of up to 20% in output just by lightly sanding the contact surfaces of brand new batteries that just come out of the package. (Do not sand the Gold contacts, just wipe with a cloth).

Forgot to mention the changes in electronic components, the LED and the battery output as the thermal changes effect the overall output of the flashlight. Each will react differently as the temperature changes. Individual electronic components on the circuit board of the same type, (a resistor for example), will change value inconsistently from one board to another. And that value change also effects the flashlights light output. 

This is what I have observed in the last 5 years of building and testing about 8000 flashlights. 

I find the spreadsheet very useful in making comparisons between LEDs deciding which LED to use in new flashlight designes and updating the older flashlights that we make.

Curt


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## HarryN (Oct 8, 2009)

I had somehow missed this very useful thread.


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