[dorkbotsea-blabber] LED color spectrum

[alex at alexcphoto.com]

I have the data sheet, it has the x/y coordinates, but those only give you a single peak value on a chromatic space "map" under perfect conditions, not the full color spectrum chart with all the variables to my specific build. with the x/y from the data sheet I can also get a rough color temperature of ~7500k. but that still is just a single value, since I am dealing with white light, it will have values thought a good portion of the visible spectrum, its that "wave length intensity throughout the visible spectrum" (not sure what its proper name would be) chart that I am looking for..

However, there are three wild variables that will affect the "perfect world" estimates on the data sheet. I am pushing these LEDs a hair past there median value, this will effect there color, in addition I am putting a filter in front of them to "warm" the light as white LEDs are often a little "cold" or blueish. with that filter I end up some where near 6700k which is closer to daylight, however this is an estimate off of an estimate,.. and the filter itself will alter the color spectrum more than just warming it a bit. and finally, heat dissipation will effect the LEDs, so depending on how well I am piping heat away from 24 ultra bright LEDs (or 32 on the new build I am working on) will also alter the numbers from the data sheet. 

Also with the first build (the one documented) I am powering it straight from a battery with resistors limiting the current, however this is not a fixed current system as the batteries slowly discharge and wander down from peak charge the light will slowly fade and the output color values slowly warp,.. I was hoping to see by how much throughout the charge. On the second build I am making a current regulating circuit with a warning light when that system falls below a point this will ensure even light both in magnitude and in color output for most (~90%) of the battery charge. but all the other variables still apply so I wanted real world numbers for that one to.

The fact is there are to many variables to consider the limited data on the data sheet (even if it was complete) anything more than an approximate guideline, If I was building a flashlight, this would probably be fine, the eye can adapt, but since I am a photographer, wanting to build a detailed color correction profile for my camera,.. and compair a few other details of this data, Unfortunately its not quite enough.

But if its not easy, don’t stress it,.. I may be taking this farther than it needs to go,.. I can gleam a rough read out using my camera and a close to pure white card,.. this is what most photographers do, and its probably close enough,.. even though it leaves out a few low impact variables, But I was just curious if I could get exact numbers to factor into a few of my experiments. That and my white card Is old and not exactly white anymore,.. So ill need to get a new one, and build a light tight pure mat black box.

To answer the other posts,. 

Chris, I had not though of using my screen calibrator to read the color of the LEDs,.. Ill have to consider that, although my output may be to intense (on the second build) for a screen reader to handle, (~380 lumen per light head) without Distance or filtering,.. Which would then alter the reading... and Im not sure how id set up the read, or how id get the data out of the spyder in chart form,… again ill have to consider that and hopefully not burn out the eye on my spyder. =) 

Chuck, don’t stress it,. If its not up and running, then its not that important,. I just like to get as precise data as possible,… some times a hair more than I need =) I’ll see what I can get off my camera using the white card,. Hopefully I’ll be able to line up the histogram with a wavelength chart. I’ll explore that first, rather than ask you to put your contraption back together. The other projects well,.. there are a few, one where I am using specific wavelengths of light to penetrate the skin and get beneficial medical reactions (think biological color/light therapy,.. I am not sure what its really called, it’s a little “wo-wo” but its a fun experiment) and another project that’s a cool blinky thing for an art/burner project where I don’t really need exact numbers on,.. But if I was going to measure the others,.. Well why not this one to,.. right,.. =),.. and a few others projects still,.. I am active on multiple projects at the moment, many of them dealing with color wavelengths and LEDs,.. probably to many,.. =)

Alex


--- wiml at hhhh.org wrote:

From: Wim Lewis <wiml at hhhh.org>
To: A discussion list for dorkbot-sea <dorkbotsea-blabber at dorkbot.org>
Subject: Re: [dorkbotsea-blabber] LED color spectrum
Date: Tue, 17 Jun 2008 20:49:20 -0700

On Jun 17, 2008, at 4:34 PM, <alex at alexcphoto.com> wrote:
> I recall some one having a gizmo that could fairly accurately  
> measure the color spectrum of LEDs (presumably any light source)

Yes, I remember somebody brought a spectrophotometer by a couple  
years ago... digging through the archives, it looks like it was Chuck  
Harrison?

If you can figure out the original manufacturer of your LEDs, you  
might be able to get a spectrum from the data sheet (either for that  
specific LED or for all the LEDs they make with that process/material).


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