Comment 5614

By Ted Mitchell (registered) | Posted February 23, 2007 at 12:33:34

Good analysis! But many raise the issue of the quality of light produced.

Basic incandescent light bulbs are pretty bad for CRI (color rendering index). This is a 0-100 scale where 0 is black and white and 100 is the quality of color produced by noon sunlight. Some people wrongly list all incandescents as "100" because their radiation is of the "blackbody" variety. At a much lower temp than sunlight a much redder spectrum is produced. Typical cheap ILB's rate about CRI 80 (they are very yellow).

Much better is the neodymium glass bulb (e.g. GE Reveal). This is a typical IDL filament perhaps burning slightly hotter (shorter life), with different glass around it. There is no sign of yellow light, it appears white. The CRI is 90+. If you haven't tried one, do it.

4 foot flourescent tubes have both a color temperature and CRI rating. E.g. 2800K means this is approximately the color of a filament at this temperature (fairly red light). 5000K is like typical sunlight. 6500K is equatorial noon sunlight (will look very bluish is the brightness is less than sunlight), etc.

CRI is typically 70 or less for "cool white" which is also 4100K. STAY AWAY FROM THIS CRAP. Most people have no idea that these are obsolete.

The T12 "cool white" can be replaced directly with a T8 3500K CRI 85 bulb (called "835": 8 is the CRI decade, 35 is for 3500K) which is actually the same $2 price, but even MORE efficient and has better color rendering than a typical IDL.

The best CRI you can get easily is the "sunlight" bulb, either a T12 5000K CRI 90 or the better T8 5000K CRI 95, both about $6. These use expensive phosphors that are also slightly less efficient than the 8 series (CRI in the mid 80's)

CFL's do not have these numbers listed or even available. So maybe they might be 2800K and CRI 82 like a typical IDL, or maybe something much worse. Probably not better though, even though this is well within current technology.

LED, who knows? Certainly the LED flashlights I have are quite bluish and likely poorly rated for CRI. But there is certianly a lot of potential there.

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