CRI ratings - how useful are they?

[Marc Galerne]

But it turns out that with a bit of correction a color chart is rendered rather well, so the low rating is unjustified as a universal measure. The CRI system is a good heads up for potential problems, but doesn't seem to be of much real help when trying to make choices between lamps for use in film/video.

Maybe with correction you can improve the CRI, but I am not even sure about that. Maybe someone out there have the answer. But I know you can correct Color temperature. You can adjust it and use any kind of light bulb. But each time you are doing this you are losing stops. That is why the idea is to go with something which as close to perfection as possible and then do your creative perception of the scene.

[Marc Galerne]

I think I mentioned somewhere recently in a post on here about HMI bulbs that they're used in follow spots a lot these days. Well the Xenon bulbs are getting quite a bit of use for that too. They have a much higher lumen per watt rating than HMI bulbs so more efficient. When you see the huge moving beams cutting into the night at some place in your city (like a night club or whatever trying to attract people there), its generally a Xenon these days.

 

Xenon is less efficient than HMI. It is so widely used as event lighting (for searchlight effects) and military because they produce a short arc that makes them ideal for parabolic refllectors and therefore produce an extremely visible beam at long distance.

Maximum lumen per watt for Xenon is 50 when HMI lamps (in our business) are beyond 80 (200W single-ended) up to 95 (18Kw Double ended) as per Osram data sheets.

Overall classification of light source : http://en.wikipedia.org/wiki/Luminous_efficacy

[Marc Roessler]

Xenon is less efficient than HMI. It is so widely used as event lighting (for searchlight effects) and military because they produce a short arc that makes them ideal for parabolic refllectors and therefore produce an extremely visible beam at long distance.

 

Marc Galerne is right here... and efficiency is even smaller for smaller xenons. That's why they aren't used in car headlights: not enough light output for the energy spent. So far it seems you can say that for any light technology, lower CRI means more efficiency.. Glamourous looks do come at a cost! ;)

 

The short arc is also important for applications in movie projection. Carbon arc has a rather short arc, xenon has a rather short arc... in contrast, engineers were always struggling with incandescent lamps: you had to use a lens behind the film gate to get the light through the gate (Philips/Kinoton did this for their incandescent version of the FP20/FP30)...

 

Karel, the lights you pictured are normal tungsten bulbs, not the xenon short arc lamps or HID "xenon" car headlights mentioned before.

Edited June 1, 2009 by Marc Roessler

[Tim O'Connor]

Had a chance to snap these while quickly walking by the lamp/bulb section at my local Lowe's. Some of the fluorescent fixtures have now added color temp. values to their packaging. Didn't get a chance to investigate so I offer no opinion other than this marks some kind of cultural/consumer info. change, I guess.

[Karel Bata]

So how many people buy the 5000K over the 3200K thinking they're getting more of something for their money..? :D

 

I've just got back from Venice and noticed there just how many tourists had the most amazing cameras - a triumph of marketing on the part of Nikon, trailed by Canon. Most no doubt were set to auto, but it must mirror some kind of growth in the visual/technical literacy of the lay public. And I'm sure I'm not alone here in wondering if that's really such a good thing...