Lights and color

Because I am looking ahead to a design for copy stand type mounting, I needed a light panel (because a softbox pointing up doesn't work very well with a copy stand.) I got one. But was curious how the light compared to the CFLs in a softbox that I have been using for camera scanning. So I did a quick comparison.

Here are how the LED light panels tested:

and here is how the softbox/CFLs tested:

Hmm, the Artograph light panel has a CRI of 74 and a TLCI of 52. R9 is -22.7 (which is very bad.) The Genray panel is much better with a CRI of 89, and a TLCI of 82.4. R9 is 59.0. The Tracer is in the middle with CRI of 80.1, TLCI of 67.7, and R9 of 11.7. (R9 == 11.7 == miissing something important.)

Even though the CFL spectrum is spikey, it tests a lot better. The CFLs have a CRI of 91.5, a TLCI of 84 and R9 is a healthy 66.2.

(I will expand the explanations of CRI, TLCI, R9, etc. some time in the future. And do more image testing.

Basically, CRI is how the human eye (but not cameras) render color. 100 is perfect, lesser numbers are worse. TLCI measures how digital cameras (but not human eyes) render color. Same scale as CRI. R9 is saturated red (on the test chart). If a light source can't rended R9, then it can't render bright reds. A lot of us like red. The standard measurement for CRI only measures R1 - R8. It does not measure R9.

In the meantime, Google is your friend. Especially look up TLCI! CRI measurements are common, but TLCI measurements rare (at the present time.))

But what about image quality? I shot the same slide with both lights. (This is the slide I have been testing with and it has picked up dust from spending several weeks laying on a table, being dropped on the floor, and being handled a lot, etc. Sorry.) With my camera's white balance set to daylight (no auto-white balance). Here is the image illuminated with the CFLs:

And illuminated with the LED panel

Some of the difference could be attributed to the LED having a CCT (Correlated Color Tempreture) of about 6600K-8500K and the CFLs having a lower CCT of about 5100K. But I tried changing white balance in Adobe Camera RAW and couldn't make these LED images look like the CFL one. Dunno. Write me if you want copies of the RAW files.

FWIW. And YMMV.

Contact me about questions or suggestions

Questions? Write to transidupe@frogymandias.org