what is Color Rendering Index

vdhillon · 08-02-2005, 07:32 PM

Hi,
does anyone know what a Color Rendering Index is? I ask because i'm trying to purchase a halide bulb with HID 175W HOR/T15/10K specs... I'm not even sure what all that means. But at the end of it it says it has a color rendering index of 65...is that good? what are most halides?
thanks

p.s. does anyone know where i can get a parbolic halide reflector for cheap?

inwall75 · 08-02-2005, 09:58 PM

Color rendering describes how a light source makes the color of an object appear to human eyes and how well subtle variations in color shades are revealed. The Color Rendering Index (CRI) is a scale from 0 to 100 percent indicating how accurate a "given" light source is at rendering color when compared to a "reference" light source.

The higher the CRI, the better the color rendering ability. Light sources with a CRI of 85 to 90 are considered good at color rendering. Light sources with a CRI of 90 or higher are excellent at color rendering and should be used for tasks requiring the most accurate color discrimination.

It is important to note that CRI is independent of color temperature.

Gresham · 08-02-2005, 10:39 PM

65 is pretty low. I use iwaski Eye Color Arc bulbs that have a really high rating of 96 cri. Accurate and punchy little sucker

mmakay · 08-03-2005, 10:08 AM

CRI is based on how humans perceive color compared to noon-day sunlight. It's a very important consideration if you are setting up a museum, but has little to do with what makes coral grow, or your fish tank look good.

Actually, most of the bulbs that reefers prefer are low CRI. A 10k bulb is much too blue to earn a high CRI score. Actinics only make things worse. The highest CRI lights are likely to be in the 55-65k range. Few people prefer the look of those bulbs, because you loose the fluorescent qualities that make many corals so interesting.

Gresham · 08-03-2005, 11:18 AM

Quote:

Originally Posted by mmakay

CRI is based on how humans perceive color compared to noon-day sunlight. It's a very important consideration if you are setting up a museum, but has little to do with what makes coral grow, or your fish tank look good.

Actually, most of the bulbs that reefers prefer are low CRI. A 10k bulb is much too blue to earn a high CRI score. Actinics only make things worse. The highest CRI lights are likely to be in the 55-65k range. Few people prefer the look of those bulbs, because you loose the fluorescent qualities that make many corals so interesting.

The Iwaski Eye Color ARC 150w par36 BLUE BLUE (20k) has a 85 CRI, while the 6500K has a 96 CRI. Most my bulbs that I run, are above 80 CRI. I still feel there is a difference in appaerance with corals and lower CRI.

http://www.eyelighting.com/ss/EQS-N-52-84-00006.pdf

Check the example pics of a low and high CRI and see for yourselves

vdhillon2 · 08-04-2005, 09:54 AM

For some reason i can't copy and paste a web address, i think its the computer. But if anyone has the time can you check out this ebay auction number and tell me if they think it is a good deal and a good bulb?
thanks.

Ebay auction # 4397422759

mmakay · 08-04-2005, 10:32 AM

The CRI index just tells us how much a given lamp will cause an object to shift in perceived color compared to its color under natural light. An index of 100 would mean that the color of an object under that light would appear to us exactly the same as it would under sunlight at noon (5500K).

In my previous post I typed 55-65k, when I meant 5500-6500 kelvin. (Or 5.5K-6.5K kelvin...) A 6500 kelvin bulb certainly could rate 96 CRI. (Most reefers, but not all, prefer bluer bulbs.) I think it is extremely unlikely that any 20K kelvin bulb could have a true CRI anything like 85. None of the bulbs in the brochure you linked are rated at 20K, and the "par36 Blue" clearly says that the listed CRI is "Reference value only" ... whatever that means.

mmakay · 08-04-2005, 10:38 AM

Quote:

Originally Posted by vdhillon2

For some reason i can't copy and paste a web address, i think its the computer. But if anyone has the time can you check out this ebay auction number and tell me if they think it is a good deal and a good bulb?
thanks.

Ebay auction # 4397422759

Hmmm, I'd be skeptical of a bulb that cheap. Not all 10k bulbs are created equal. Check out this page and you'll see what I mean.

Ice · 08-04-2005, 11:29 AM

most likely is a cheap bulb but for that price it would make a good backup bulb. i prefer to stick with higher quality bulbs, for a reef tank i think it's worth it to go with a good quality bulb. JMHO

Peter

Chris Jones · 08-04-2005, 03:54 PM

This is a VERY Enlightening Thread!! Pun intened. I learned a bunch just now, I think I need to lie down now.