Light bulb spectral analysis
July 10, 2010 10:10 AM Subscribe
How can I find out what spectrum of light (and what intensities of the various parts of the spectrum) are emitted by various types of light bulbs?
I started wondering this because I was thinking about blacklights and how they emit UVA radiation, which can cause sun tans, but is it enough? Does it emit more UVA than a normal fluorescent, or does it just hide the rest of the spectrum? Also, I heard that fluorescent lights emit more UV light in general than incandescent, which is a concern if you don't want things in your house to get UV damage, e.g. art, furniture. But again, the question is how much is emitted? What about the so called "full spectrum" light bulbs that are more expensive but look better? Is there any source that makes available spectral analyses of various light bulbs?
I started wondering this because I was thinking about blacklights and how they emit UVA radiation, which can cause sun tans, but is it enough? Does it emit more UVA than a normal fluorescent, or does it just hide the rest of the spectrum? Also, I heard that fluorescent lights emit more UV light in general than incandescent, which is a concern if you don't want things in your house to get UV damage, e.g. art, furniture. But again, the question is how much is emitted? What about the so called "full spectrum" light bulbs that are more expensive but look better? Is there any source that makes available spectral analyses of various light bulbs?
You can use a spectroscope. Or build your own spectrometer from a CD and a cereal box.
posted by Civil_Disobedient at 12:26 PM on July 10, 2010
posted by Civil_Disobedient at 12:26 PM on July 10, 2010
Unfortunately, the CD spectroscope won't work for UV, as UV is invisible.
posted by fake at 12:32 PM on July 10, 2010
posted by fake at 12:32 PM on July 10, 2010
And the term you're looking for with fluorescent light bulbs is Color Rendering Index (CRI) which describes the "fullness" of the spectrum. The way fluorescent lights work you don't have a continuous spectrum like with incandescent; the spectrum is "faked" using a combination of coatings inside the tube (similar to how a CRT fakes white by adding red, green and blue light). Colors shifted towards the higher end of the spectrum (>6000 K) are described as "cool" because they contain more blue, while tubes that are designed to emphasize the lower ends of the spectrum are called "warm" (and have more red). But if you look at a fluorescent through a spectroscope you'll see chunks of spectrum missing. This is why designers and illustrators use high-CRI tubes: the more full the spectrum, the more accurate the colors of the things they illuminate.
posted by Civil_Disobedient at 12:36 PM on July 10, 2010
posted by Civil_Disobedient at 12:36 PM on July 10, 2010
Uh, yes as fake says this is only for visible light.
posted by Civil_Disobedient at 12:38 PM on July 10, 2010
posted by Civil_Disobedient at 12:38 PM on July 10, 2010
The whole point of a fluorescent lamp is that it is a UV source with a coating that converts UV to visible, so in general any UV that leaks through is wasted potential and is to be minimized. From GE:
UV exposure from sitting indoors under fluorescent lights at typical office light levels for an eight-hour workday is equivalent to just over a minute of exposure to the sun in Washington, D.C. on a clear day in July.posted by Rhomboid at 12:45 PM on July 10, 2010 [1 favorite]
This thread is closed to new comments.
Some manufacturers provide SPD information. Here's a tool from GE, for instance. Color temperature is the standard specification, however.
posted by mr_roboto at 12:25 PM on July 10, 2010 [1 favorite]