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   fun with a spectroscope
Monday, March 24 2008
The other day I had a novel idea about a way I could secretly spy on the lives of the neighbors. It had to do with information they were broadcasting freely from their windows, and it was in a far higher part of the spectrum than their WiFi. I was thinking about whether or not it would be possible to use a spectroscope to analyze the stray light from their interior lighting to see whether or not they were using compact fluorescent bulbs. This could be worked into a systematic study to determine how large the actual installed base of CF bulbs actually is, perhaps correlated by income. My guess is that people with more income and higher education (and more gadgets) will tend to have more of the bulbs (they save money in the long run, but they cost more up front). Indeed, if a spectroscope can determine which houses have CF bulbs, a savvy burglar could better narrow his focus on the houses most likely to contain expensive leading-edge gadgets and other items containing concentrated monetary value.
When these thoughts first occurred to me, I wondered how I could lay my hands on a cheap spectroscope. A little googling turned up a $9 quantitative spectroscope at a site called After I'd already made my purchase, I went poking around the site for other fun things and stumbled into a treasure trove of material for a righteous homeschool creationist biology curriculum. How embarrassing!
The other day when the spectroscope arrived, I went around examining various light sources with it to look for obvious differences among them. I was astounded by how vastly different CF light is from seemingly-identical incandescent light. While incandescent bulbs produce a continuous spectrum of colors blended together in a rainbow, CF units produce light only in a series of four or five narrow bands (red, yellowish-orange, green, cyan, and bluish-purple) isolated by broad swaths of nothing. If one can get reasonably close to someone's window at night, it would be a simple matter to determine if their lamps contained CF bulbs or not using only a $9 spectroscope.
Incidentally, LCD displays (which are backlit by fluorescent bulbs) also have this characteristically-banded light, though CRT light is continuous-spectrum, as is the light of the Sun, the Moon, and other objects illuminated by the Sun. Interestingly, old-school fluorescent tubes (the familiar industrial kind) can produce nearly-continuous spectra, depending on its characteristics. A cheap $1 SunbriteTM CF bulb I'd once bought at a dollar store produces a ghastly bluish light, but its spectrum is far more continuous than that of the bulbs I prefer. I also have a handful of 120 volt LED bulbs, and the spectrum of their hideous bluish light is close to continuous, though it has a dark band where there should be cyan.

A continuous spectrum (typical of light from incandescent bulbs and the Sun).

Spectrum produced by a compact fluorescent bulb (they vary).

Today was a sunny day, though temperatures never climbed out of the 40s. In this weather the cats are tempted to go outside, though (with the exception of Clarence), they don't stay out for long. (When there is snow on the ground Clarence is the only cat who goes out at all.) Sally also likes to be outside in this weather, and she can typically be found sunning herself impatiently in the driveway, waiting for someone to either come or go. She is the most chronically-bored animal I have ever known.

Reading an article at, I came upon the Irvine Housing Blog, sort of a schadenfreude central for housing bust celebrants in Irvine, an edge city south of Los Angeles. The site features entertaining and well-written analysis of the depth of the housing crisis in Irvine, but it also includes a lot of filler, mostly in the form of lyrics to stale old pop songs much better heard than read.

For linking purposes this article's URL is:

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