51 of 56 people found the following review helpful
Fantastically White (with this little green you pay for it),
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This review is from: Cowboystudio Full Spectrum Light Bulb- Four 45W Photography Photo CFL 5500K - Daylight balanced pure white light, (Pack Of 4) (Camera)
The first question in my mind is, is it truly "full spectrum" white? So I set up a very simple way to measure it. I am sure that it is not perfect by many scientists' standard. I am limited to the resources at my disposal.
Using a Da-Lite projector screen as the background and a standard desk lamp as the housing for the light source (I don't have a studio lighting setup yet), I set my Canon T2i to raw mode. Except for auto exposure, the camera does not do any auto processing including ISO. The photos are then imported into Photoshop without any kind of enhancement. The center point of the image is sampled and Photoshop can tell me the color composition of that sample.
For comparison purposes, I also measured two other light sources: Canon 430EX flash light and Feit 18W(75W equivalent) household CFL with "Daylight" color temperature. The results are color charted in Excel and uploaded to this product page above. They are surprising.
To be "full spectrum" or white (either terminology is not quite precise), the strengths of the three prime colors need to be equal. The strength is number between 0 and 255. (0,0,0) is pure black and (255,255,255) is pure white. Human eyes are usually quite tolerant of difference in the single digit range. Most people, including me, would expect the $300 Canon speed light to be a very color neutral light source. But no. It actually has a visible blue tint. It is only marginally better than the $1 Feit "Daylight" household CFL. I am not suggesting that a flash light and a CFL are interchangeable, it is nevertheless disappointing that the Canon can't get a tight color balance in that expensive device. The best one, by a significant margin, is the Cowboystudio photo CFL. It is amazing that a cheap CFL like this can produce such tint-less light. The difference among the three colors are less than 5 percent, and not visible to me (and probably to most people). I'd conclude that it does live up to its claim of being a "full spectrum photo light."
One thing that puzzles me is that when I looked at the exposure data, I found that the aperture and shutter combinations used for 45W and 18W CFLs photos are almost the same (the distance to the screen is the same). I had expected at least one stop difference. That might be due to the fact that the 45W CFL is so big and long, the shade of the lamp can't reflect well. But I am not quite sure.
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Showing 1-3 of 3 posts in this discussion
Initial post: Mar 12, 2012 1:56:39 PM PDT
Joshua Powlison says:
I must say, I am really impressed by this review. Thanks for the info!
Posted on Jan 4, 2013 12:01:34 AM PST
Thanks for taking the time to do that... very helpful! But I so have a nitpick with your terminology: Your test with only three data points per bulb (Red, Green, Blue) cannot determine whether a bulb is "full spectrum" or not... that would require a large number of measurements at different wavelengths and would surely show that like all CFLs, this does not have anywhere near full spectrum. You seem to know this yourself because you said the terminology is precise so this is for the readers not the review author.
What you are really measuring is the color balance from the camera's perspective, and you have determined that for your camera (and settings) these are closest to daylight color balance, with no significant green shift. "White" is a good term for this, in the photography realm.
Posted on Nov 10, 2013 10:25:24 AM PST
The Speedlite has a Color Rendering Index (CRI) of very close to 100. It is better than any fluorescent lamp. You can remove any slight tint by using the camera's custom white balance, or by setting the white point in Camera Raw (or other raw conversion software you use). Due to the spectra of the phosphors used, no fluorescents can render colors as accurately as incandescents, flash tubes or sunlight. The white point (which was what your test was looking at) can be easily fixed after the fact, but inaccurate colors cannot.
A good way to test light sources is to use a calibrated color chart, such as the X-Rite ColorChecker, or similar. Amazon sells several different ones. Using one of these charts, you can usually see color problems with your naked eye, and you can also photograph them and compare your RGB colors with the expected colors. You can also use them to set the white point in Camera Raw; just click one of the gray boxes with the eye dropper tool.
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