Darkroom Lighting Color Temp considerations

[Bob Salomon]

So, their claimed K is in error?

No, CRI is a different rating then color temperature. The box interior was painted with specificiallynformulated paints that evened spikes in the tubes and replaced missing colors. The diffuser was also selected to further correct the output to obtain the best CRI at 5400K as well as at 3700K. Tubes alone don’t do the job. The complete system does!

[Pere Casals]

I wouldn't use LEDs for critical viewing purposes simply because the don't emit a continuous spectrum and can do funny things with colors/toning hues.

Doremus, today there are a lot of CRI 98 LEDs (or CRI +95) that are perfectly suitable even for light tables, illumination for video, cinematography, etc.

It's just a matter to check the CRI of the LEDs in the light source before buying.

The single difference one can perceive when compared with matching sunlight or halogen is the way lower heat generation.

[Drew Wiley]

Don't rely on just advertised CRI figures. If it's the real-deal there will be a published spectrogram. What "full spectrum" LED's seem to do at this early point
in their history is simply fool the eye into thinking you've got a continuous spectrum. That might be OK for gallery lighting; but for critical evaluation in a
darkroom, with metamerism potentially at risk, I'm very skeptical. There are going to be spikes and gaps in the spectrum. And if the bulb is anything from Phillips or Consumer GE, don't believe a word they say. If something sounds too cheap to be true, it is.

[Pere Casals]

Don't rely on just advertised CRI figures. If it's the real-deal there will be a published spectrogram. What "full spectrum" LED's seem to do at this early point
in their history is simply fool the eye into thinking you've got a continuous spectrum. That might be OK for gallery lighting; but for critical evaluation in a
darkroom, with metamerism potentially at risk, I'm very skeptical. There are going to be spikes and gaps in the spectrum. And if the bulb is anything from Phillips or Consumer GE, don't believe a word they say. If something sounds too cheap to be true, it is.

Drew, if you are skeptical just check these datasheets:

http://www.lucent-lighting.us.com/me...atasheet_0.pdf

https://eu.mouser.com/datasheet/2/22...W00-255475.pdf

https://eu.mouser.com/Optoelectronic...usfj?P=1yo1i7l





Or better, just buy a 97 CRI LED or video illuminator and check it on your own for $66, search amazon for: GVM Dimmable Bi-color LED Video Panel Light Variable 29W

[Drew Wiley]

Well, there is a big burp in the spectrum at a critical spot, so I'd never trust a light source like that for critical color evaluation or matching work. The example posted is also obviously very warm K, so of little use in display; and I don't know if their cooler K versions are going to be any better. I've been looking into these for awhile. They're basically mixing LED's in the same bulb, an interesting advance that has been going on a few years, but hardly the holy grail. Basically, the "usable" CRI rating is based on a spectral hump quite different than what I'd want. That doesn't mean they're not on the right track, but
there are still some conspicuous limitations. LED video panels are a joke, a poor man's poor substitute for HMI.

[Pere Casals]

Well, there is a big burp in the spectrum at a critical spot

That minimal blue spike has no practical effect, at all, and by far. Just buy a cheap CRI 95 LED bulb for home usage and see. The 98 rating is even better, but it's really difficult to tell a difference from the 95 one.

Drew, there is no need to rely in the CRI rating, just using an spectrometer you see the reality. Another way is checking the datasheet of the LEDs used if one does not have an spectrometer.

LED video panels are a joke, a poor man's poor substitute for HMI.

LEDs are not only the future, LEDs are also the present.

If you want a particular narrow band then you have a LED doing it every 5nm... with no filter, and for white LEDs you can design the exact spectrum you want. That minimal blue spike you see in some spectrums could be eliminated with an absorbing dye, if it was not done this is because it is irrelevant.

HMI is not bad, but it has a way weirder spectrum than a high cri led, see the HMI spectrum:


Osram HMI 575W Sel UVS

[StuartR]

Personally, I am most willing to trust my eyes. I look forward to trying the new LED's at some point, but I still have yet to see anything that comes close to the Solux bulbs. To me, this makes sense. The sun, halogen and incandescent all produce blackbody radiation. Other technologies produce light with different techniques, and then try to correct the spectrum as best they can. Halogen and Incandescent already have it more or less right, they just need adjustment in color temperature. As far as I can tell, the only disadvantages of halogen are heat generation and efficiency as compared to LEDs. Their relative longevity is lower, but extends for years in good bulbs. In exchange, you get the best color reproduction, unconstrained dimmability, instant on and off, a pleasant, directional light (useful for different areas of the darkroom...more light over the viewing area than the enlarger, paper safe etc), and cheap bulbs. Where I live all the energy is renewable, so the extra energy is offset by the lower environmental impacts of the bulbs and fixtures themselves (no ballasts, circuit boards, mercury vapor etc).

This is a few years old, but the list on the website is still maintained. Pretty interesting regarding the LED's. Good stuff is out there, but it seems like it can be tricky to find.
https://www.cinema5d.com/led-light-accuracy-tlci/

[Pere Casals]

Personally, I am most willing to trust my eyes. I look forward to trying the new LED's at some point, but I still have yet to see anything that comes close to the Solux bulbs. To me, this makes sense. The sun, halogen and incandescent all produce blackbody radiation. Other technologies produce light with different techniques, and then try to correct the spectrum as best they can. Halogen and Incandescent already have it more or less right, they just need adjustment in color temperature. As far as I can tell, the only disadvantages of halogen are heat generation and efficiency as compared to LEDs. Their relative longevity is lower, but extends for years in good bulbs. In exchange, you get the best color reproduction, unconstrained dimmability, instant on and off, a pleasant, directional light (useful for different areas of the darkroom...more light over the viewing area than the enlarger, paper safe etc), and cheap bulbs. Where I live all the energy is renewable, so the extra energy is offset by the lower environmental impacts of the bulbs and fixtures themselves (no ballasts, circuit boards, mercury vapor etc).

This is a few years old, but the list on the website is still maintained. Pretty interesting regarding the LED's. Good stuff is out there, but it seems like it can be tricky to find.
https://www.cinema5d.com/led-light-accuracy-tlci/

This doc states CRI 90 "is widely regarded as the minimum for television use", but we are talking about CRI 98 LEDs !!!! there is a big leap from 90 to 98. At 98 no pro colorist will see a flaw.

[StuartR]

Did you watch the video? CRI is not infallible...it is a 1960s standard that applies only to standard pastel like colors, it is not a great measure of accuracy or a lights suitability for use in color critical applications. It is a basically a minimal standard, but the only one we have. The colorist mentioned how some high CRI lighting is actually worse than lower CRI in some cases etc. There is a comprehensive list of lights that they have tested. I do not disagree that there are LED's available that are great at color reproduction, but I think your chance of getting one off the shelf is still pretty low unless you specifically seek out particular brands and models, or have the time and ability to test.

[Tin Can]

Thanks for the Link which has a Link to actual lights we could buy. The Filex at B&H looks interesting and affordable.

So many obfuscate with unproven theory and dim references to high personal standards.

Here and now available product referral is welcome.

Personally, I am most willing to trust my eyes. I look forward to trying the new LED's at some point, but I still have yet to see anything that comes close to the Solux bulbs. To me, this makes sense. The sun, halogen and incandescent all produce blackbody radiation. Other technologies produce light with different techniques, and then try to correct the spectrum as best they can. Halogen and Incandescent already have it more or less right, they just need adjustment in color temperature. As far as I can tell, the only disadvantages of halogen are heat generation and efficiency as compared to LEDs. Their relative longevity is lower, but extends for years in good bulbs. In exchange, you get the best color reproduction, unconstrained dimmability, instant on and off, a pleasant, directional light (useful for different areas of the darkroom...more light over the viewing area than the enlarger, paper safe etc), and cheap bulbs. Where I live all the energy is renewable, so the extra energy is offset by the lower environmental impacts of the bulbs and fixtures themselves (no ballasts, circuit boards, mercury vapor etc).

This is a few years old, but the list on the website is still maintained. Pretty interesting regarding the LED's. Good stuff is out there, but it seems like it can be tricky to find.
https://www.cinema5d.com/led-light-accuracy-tlci/