Lightbulb spectra on the cheap

There’s been some talk around the blogosphere about the new lightbulb proposal for Australia. I must admit that I’ve been a compact fluoro nut since the late 80’s, when I bought a 30 dollar lightbulb out of a Greenpeace catalog for Christmas.

There’s tons of theory about lightbulbs that I’m sure smart bloggers would love to spend hours talking about. Some of the explanatory physics can be found here. But despite the numerous off-topic rants that I post, this blog is allegedly about analytical techniques. So instead of pontificating, I’ll just show my spectra.

In order to get a spectra, you need a spectrometer- any device that is capable of breaking down light into its component wavelengths. Most households have dozens of potential spectrometers lying around, for most of the indoor spectra shown here, I used U2 (see figure).


For the streetlights, I used a crappy old Indigo Girls CD that I haven’t touched since I stopped asking lesbians out about a decade ago. I recommend something similarly expendable for outdoor use. If you’ve put all your music on an iPod and chucked all your CD’s, bad luck.

So, below is the spectrum of an incandescent light bulb, generated by reflecting the light off of a compact disk at an appropriate angle, and photographed with a digital camera equipped with a macro setting:


Note the relatively dim blue and the continuous color all the way through the rainbow.

A cheapo Phillips compact fluoro follows:


As you can see, the light is broken up into discrete color bands, with gaps in between. Note also that there is a fairly strong violet emission, a region where the incandescent was fairly weak.

Here is a modern Nelson compact fluoro, of the “cool white” variety:


Note the gaps between the violet, blue, and green have been partially filled, but that the spectra is still not smooth.

Streetlights have spectra too. Here is an orange light- probably a high pressure sodium lamp.



And here is a bluish streetlight.


I tried doing some stars as well, but even with Sirius almost directly overhead, I couldn’t get enough light to get any colors using this method.

How this all relates to energy efficiency is a whole different story, but the point is that anyone with an old U2 CD lying around can determine what sort of light is given off by various sources. So baby, baby, baby, light my way- and I’ll tell you what colors it contains.