D50 lighting vs. 5000k - Solux 4700?

Discussion in 'Digital Darkroom' started by scott_august, Mar 5, 2004.

  1. I have been using Philips 930 T8 florescent tubes for lighting in my
    digital darkroom. I selected these lights because they have a 97% CRI
    and I have heard they are the exact same bulb as the ott-light uses.
    I have noticed that it has a distinct green cast which is totally
    useless in refrencing the prints from my Epson 9600 Ultrachrome.

    I have now added a second light fixture and put Sylvina Design 50 T12
    tubes in it. They seems to have a redder/magenta cast to them which
    actually seems very close to daylight. If something looks good under
    the Design 50 lights it still looks good outside or under Tungsten
    lighting. I also have a Gepe Slide viewer that claims to be 5000k
    daylight and it has a similar cast to the Design 50 tubes.

    I have been reading about D50 lighting vs 5000k. It sounds like 5000k
    can be inconsistant between manufactures but D50 is an imaging
    standard. I have been looking at getting Halogen MR16 4700k lights by
    Solux. They claim to be D50 and highly regarded as the best D50 bulb.

    Does anyone have experience with these bulbs and the epson
    Ultrachrome 7600/9600?

    I don't want to order a bunch and put tracklighting in my work area
    if I don't have to.
  2. I've got them. I built a "viewing wall" that uses three of the Solux lamps. They work fine and deliver a nice pleasing light that is difficult to tell from real daylight. I use them for viewing work prints from an Epson 7600.

    I would warn you away from Solux's track light fixtures, however. I bought a set, had to return them because they couldn't hold position (they rotated when they got hot), got another set which also rotated, and had the added bonus of the paint blistering due to the heat. So I returned them also. The Solux people were less than helpful with this.

    Bottom line is that they are just cheap fixtures. They also have the annoying property of bouncing the stray light from the bulbs out the back of the fixture onto the ceiling (a real glare source). End the end, I replaced the cheap Solux fixtures with Halo L2770PX fixtures. Much nicer, but more expensive. At least they stay pointed where I point them, the paint doesn't blister off, and they contain the stray light.

    The Solux people make a great D50 lamp. Everything else I would stay away from. Of course, YMMV.
  3. Scott,
    The problem you are running into is the difference between the smooth spectrum of natural light and the spikes seen in any fluorescent light. The Philips bulbs are one of my favorites for general use (the TL950 series is better still), but they are not optimal for evaluating metameric pigments such as the UltraChrome inks. These inks (specifically the yellow) change color depending on the wavelength of light hitting the paper. A smooth spectrum bulb, surch as a Solux, gives a less distorted and more predictable view of how the print looks.
    D50 is a theoretical construct, not a real lighting condition. A 5000K light simply has the correct average color temperature; this says little about the smoothness of the light spectrum. The chart below compares, in order of increasing price, the output spectra I measured from an Ott-Lite True Color, a Solux MR-16 bulb, and a GretagMacbeth Sol-Source. A Phiilips TL950 has more pronounced spikes than the Ott-Lite. Ott-Lite or Philips bulbs work reasonably well with prints that have no metamerism problems. Unfortunatley, as you saw, this is not the case with Epson UltraChrome prints.

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