I do some minor upgrade of flashlights, therefore I often work with LED datasheets. Unfortunately it is not really exciting. I have to find the datasheet, then find the graph, determine the value, find it in a table to determine another value, and then multiply these two.
Simple, that’s true. But tiring too.
I think, however, that there’s no need to do this boring work since we all have a tool for such tasks just at hand. We only have to use it correctly.
And it seems like I’ve figured out how to do it. At this page you can find out the luminous flux and power consumption of a LED at the given temperature or compare several LEDs. (Notice: calculation in made on the basis of an average luminous flux for the given bin, while datasheets usually show the minimum.)
Note: the presented tool is not a reference guide and it shall not be used instead of a datasheet. For example, the maximum current for Nichia 219 is 1.5A, while the graph is constructed (and input into the LedCalc database) for the figures up to 2A.
Very cool. Would be even better if you could add fields for electrical and optical efficiency like the CREE tool (such things are always merely an estimation of course, but I still find it useful).
It’s imperative to include an estimation of the thermal resistance from the LED to ambient in such calculations. You can’t just select a current and a temperature.
I already made this spreadsheet for you a long time ago. It has proved pretty accurate for my use.
I’m working on the inclusion of Nichia 219 which is difficult as Nichia’s data sheets are based on ambient temperature rather than junction temperature (Cree).
[Edited]
As a coincidence we have used the same name for our products.
sixty545, our database “FONAREVKA.RU. LED Calculator” was established in 27 January 2011, ie half a year before your calculations (Your program has been published 14 June 2011).
No offence!, I have corrected my first post.
Your calculator is fast to use and has a good diversity of LED’s to choose from and seems to be good to predict light output from a LED with a junction temperature of what you chose (default 25 degr C). But the LED temperature is a function of thermal resistance and the part of power that is not emitted as light energy. So it is hard to guess the final LED temperature for a project.
BTW You have a very interesting NON-PWM driver, AVSel, on your site that I would like to try out. Unfortunately I cannot import goods with a value higher than $13 so I guess I am stuck with PWM.
I wonder why no-one in BLF has made a review of that driver. It looks quite innovative.
Has the MCU program been published?
cainn,
It’s possible, but I’m not sure that I understand correctly how the electrical efficiency affects the result.
Could you please explain to me this question?
sixty545,
personally I am not sure that influence of temperature can be considered really precisely, because it’s hard to measure junction temperature. This feature appeared demanded, but I still believe that it is simpler to measure a flux, than to consider all factors influencing it to calculate accurate value.
Maybe I’m wrong.
@Virgo_Style:
Hi, this is extactly what I mean. The calculator should calculate the resulting temperature so one can see if the max. temperature is exceeded (150 degr.C). You can only do this if you input (estimate) the total thermal resistance the LED sees, which includes knowledge (experience) about the host.
You also have to take in consideration that a part of the power (20-40%) is emitted as light and does not contribute to the heating of the LED.
Difficult? Yes, but I have done it in my spreadsheet where the LED temperature will be shown in red if it is calculated to be over 150 degr.C. I have also extrapolated the datasheet curves to extend the current input range to twice the nominal max current for the LED ie. 6A for XP-G.
If you could include a thermal calculation that would make it a great tool!
I have not enough knowledge myself to concatenate my spreadsheet into something simpler, therefore I use one spreadsheet pr. LED type. The used formulae also differs from LED type to LED type.
Just want to say Thanks for providing this handy tool; Bookmarked and used.
Saved me a bunch of tedious time and eye strain on the Cree data sheets already.
Just a suggestion, (since you already have it with Watts); Post the Vf as well.
