White LED lumen testing

[jtr1962]

I saw your this thread Forum on caculating lumens for white leds... http://www.candlepowerforums.com/vb/showthread.php?89607-White-LED-lumen-testing .....

I have this flash light DP-722b... I want to know its LED Lumens and Watts...

I am sending you its Datasheet... It is 5mm Straw Hat LED... can you please find it out for me the exact Lumens and watts for it..

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

Unfortunately, data sheets are often wrong, especially with generic Chinese LEDs. The only way to determine to lumens and watts is to actually test the LED. In fact, that's the reason why I started testing LEDs in the first place-because the data sheets either didn't exist, or couldn't be trusted.

Unfortunately, I stopped testing LEDs a while back on account of lack of time, and I doubt I'll ever have time again in the near future. All I can tell you is in all likelihood your flashlight is putting out less than 5 lumens per LED. 5mm LEDs just can't put out a lot of light due to their poor heat dissipation limiting the currents they can be driven at.

 

[Farhaj]

Unfortunately, data sheets are often wrong, especially with generic Chinese LEDs. The only way to determine to lumens and watts is to actually test the LED. In fact, that's the reason why I started testing LEDs in the first place-because the data sheets either didn't exist, or couldn't be trusted.

Unfortunately, I stopped testing LEDs a while back on account of lack of time, and I doubt I'll ever have time again in the near future. All I can tell you is in all likelihood your flashlight is putting out less than 5 lumens per LED. 5mm LEDs just can't put out a lot of light due to their poor heat dissipation limiting the currents they can be driven at.

You know any mathematically ways to calculate lumens per LED for the White Genereic 5mm LED.. according to the data given in data sheet..

I have these some data and pictures of LED..

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[jtr1962]

You know any mathematically ways to calculate lumens per LED for the White Genereic 5mm LED.. according to the data given in data sheet..

Just see what I did in my spreadsheets. I have links to my spreadsheets in the first post in this thread. If the data sheet has a graph for the light intensity versus angle you can normalize the numbers (if they haven't been normalized already), plug them into the spreadsheet, and then use the center intensity to get a rough approximation of the total lumens. However, this approach is far from exact because data sheets are often incorrect. Seriously, you can get a decent approximation with far less trouble by just measuring the current and voltage going to the LED, and multiplying by 75 to 100. For example, if the LED is being driven at 20 mA, and the voltage across it is 3 volts, then the input power is 0.02 x 3 = 0.06 watts. Most generic white LEDs these days achieve 75 to 100 lumens per watt at their nominal current (i.e. 20 mA for 5mm LEDs), so just multiply 0.06 by 75 to 100. That gives you 4.5 lumens on the low end, and about 6 lumens on the high end.

The only other way to get more accurate values is to actual measure the intensity at different angles then plug the numbers into a spreadsheet as I did. I had to make a jig to do this, and it's very time consuming which is why I don't do it any more.

 

[Farhaj]

Just see what I did in my spreadsheets. I have links to my spreadsheets in the first post in this thread. If the data sheet has a graph for the light intensity versus angle you can normalize the numbers (if they haven't been normalized already), plug them into the spreadsheet, and then use the center intensity to get a rough approximation of the total lumens. However, this approach is far from exact because data sheets are often incorrect. Seriously, you can get a decent approximation with far less trouble by just measuring the current and voltage going to the LED, and multiplying by 75 to 100. For example, if the LED is being driven at 20 mA, and the voltage across it is 3 volts, then the input power is 0.02 x 3 = 0.06 watts. Most generic white LEDs these days achieve 75 to 100 lumens per watt at their nominal current (i.e. 20 mA for 5mm LEDs), so just multiply 0.06 by 75 to 100. That gives you 4.5 lumens on the low end, and about 6 lumens on the high end.

The only other way to get more accurate values is to actual measure the intensity at different angles then plug the numbers into a spreadsheet as I did. I had to make a jig to do this, and it's very time consuming which is why I don't do it any more.

there are forumlas given on this page to convert various data into Lumens.. I used this http://www.rapidtables.com/calc/ligh...a-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 explain..

Also, tell me where is that spreadheet which you are telling that can be valid for the Geric 5mm Strawhat chinese LED as this one http://underwaterseaplants.awardspace.com/led.pdf

 

[jtr1962]

there are forumlas given on this page to convert various data into Lumens.. I used this http://www.rapidtables.com/calc/ligh...a-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 explain..

All these conversion tables make assumptions about the light distribution of the LED. In other words, they are at best approximations, which is why they may not agree with reality. As others have been trying to tell you in the other thread, you can't directly convert candela to lumens unless you make measurements of the light intensity versus angle as I did.

Also, tell me where is that spreadheet which you are telling that can be valid for the Geric 5mm Strawhat chinese LED as this one

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

Here is a .zip file containing all my spreadsheets. Unfortunately, this won't help you here because the datasheet for the LED you're interested in doesn't have a chart for intensity versus angle. Why don't you just ask the manufacturer how many lumens this LED puts out? They would know better than anyone here.

 

[Farhaj]

All these conversion tables make assumptions about the light distribution of the LED. In other words, they are at best approximations, which is why they may not agree with reality. As others have been trying to tell you in the other thread, you can't directly convert candela to lumens unless you make measurements of the light intensity versus angle as I did.


Here is a .zip file containing all my spreadsheets. Unfortunately, this won't help you here because the datasheet for the LED you're interested in doesn't have a chart for intensity versus angle. Why don't you just ask the manufacturer how many lumens this LED puts out? They would know better than anyone here.

I asked them and they straight away said per led is upto 7-10 lumens or something like that.. so not sure they are telling the truth.. the datasheet has the Angle , mcd and Wavelenghts mentioned in it... can it not help to find the lumens from it... http://underwaterseaplants.awardspace.com/led.pdf

 

[Farhaj]

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:

 

[Farhaj]

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..

 

[WhiteRabbit]

Great job! The OP is exactly what I've been looking for... except that of course it doesn't include led's from the last 5 years. Is there anything just like this, but which covers current white LED's?

 

[jayrob]

jtr1962,

Wow I was just reading some of the testing you have done on various LED's...

Very impressive work! Thanks very much for sharing all of your work with us.

There is so much information in the thread, that it is hard to sift through and find what I'm hoping to find, and that is information on the SST-90, and more resent MT-G2 6V 5000K emitter.

Have you got a chance to test those?

 

[jtr1962]

jtr1962,

Wow I was just reading some of the testing you have done on various LED's...

Very impressive work! Thanks very much for sharing all of your work with us.

There is so much information in the thread, that it is hard to sift through and find what I'm hoping to find, and that is information on the SST-90, and more resent MT-G2 6V 5000K emitter.

Have you got a chance to test those?

Thanks for the compliments. I'm glad this thread is still drawing interest even though it hasn't been updated in a while.

The SST-90 results are in this post. I never tested the MT-G2 6V.

I stopped testing a while back due to lack of time. This year I've been doing a new consulting gig which leaves me very little free time. Bottom line-I don't anticipate adding to this thread in the near future. For what it's worth, LED manufacturers are characterizing their LEDs much better on their data sheets than in the past, so often you can get the information you need right off the data sheet.

 

[jayrob]

Thanks for the compliments. I'm glad this thread is still drawing interest even though it hasn't been updated in a while.

The SST-90 results are in this post. I never tested the MT-G2 6V.

I stopped testing a while back due to lack of time. This year I've been doing a new consulting gig which leaves me very little free time. Bottom line-I don't anticipate adding to this thread in the near future. For what it's worth, LED manufacturers are characterizing their LEDs much better on their data sheets than in the past, so often you can get the information you need right off the data sheet.

Thank you for your reply and again, thanks so much for all your work...