Visually measuring CRI

[Garth Herrick]

Holly,

This is interesting and revealing. Even the pinhole spectrum of natural north light seems to lack yellow in the digital camera capture.

Holly, I was afraid to show my diffraction grid pictures until you showed yours first. The camera really didn't do the spectrum any justice. Seeing that your pictures looked about the same as mine made me realize the fluorescent lamps I bought really weren't all that bad after all.

Your photos are better because you were farther from the light source than I was and you had a black backdrop to photograph the spectrum against. Last night I did't have a handy black background, and I took the left half of the photo against a foil insulation ceiling in the shadow of the light. I took the right half several weeks earlier before I changed the lamps.

Actually I did manually focus on the spectrum, but for some reason it never quite appeared to be able to be in focus as well as my eyes. I was in a rush to add a post to your thread last night, so my photo was quick and dirty. I held the loose diffraction grid in one hand slightly arched so it would not collapse, and tried to focus and shoot the picture with my other hand. all while laying on the floor. So no wonder my photo looks worse than yours. I also slightly rotated one tube to shut it off for the photo. I hope that in the short term the dual lamp ballast is not harmful to just one lamp lit.

Thanks for initiating this spectrum analysis of (nearly) full spectrum lighting.

Garth

[Richard Monro]

Has anyone done any spectrum work on the Philips F32T8 TL950 fluorescent bulbs? They have a CRI of 98 and seem to be used extensively in the print industry. They also appear to be less expensive than other high CRI lights.