DIY spectrometer to determine bulb life

[mkzimms]

Here is a fun tutorial on how to build your own homemade spectrometer. As we all know, the change in spectrum over the life of your bulbs (especially MH) can have some nasty effects on algae and coral growth as well as the overall health of your reef. There seems to be benefit to having a spectrometer around even if it is a cheap one. Take a reading at the installation of a new bulb and subsequent readings every month over 6 months to determine when your bulbs are changing spectrum. I just built one following this tutorial and will have pictures up as soon as I can find my camera.
how to make one out of a cardboard tube or cereal box
http://www.exo.net/~pauld/activities...ctrometer.html
some cool pictures of different spectrums using the box
http://www.cs.cmu.edu/~zhuxj/astro/h...ctrometer.html

 

[fishfreak1242]

Thats a pretty cool diy. How do you figure out if your bulbs are in the right spectrum?

 

[mkzimms]

well you would take an initial reading at the first installation of a new bulb and compare it to the old bulb you are replacing. from then on you would have a standard you could check against. that way you could catch a bad bulb before its manufacturer's expected life and before it starts affecting your tank. additionally most bulbs will come with a spectrum reading that you can usually find at the manufacturer's website.
here is the spectrum for a 250w 10k XM Lighting metal halide bulb... where the color peaks are is where the bright lines will show up on your homemade spectrometer. once those lines move from their original positions, the bulb is changing spectrum and giving off different wavelengths of light than was originally intended. but even with the different graphs you should see the colors peaking in the right colors.
as you can see here this bulb is in the 10K range and gives off a broad range of color in the blues and reds

this is a 250w bulb from the same manufacture that is rated in the 20K range where it is giving off mostly blue light. you can tell the spectrum is completely different with the spikes in the blue range.

you would see the differences in these two bulbs by where the dark stripes are positioned on the spectrum. these were taken from the manufacturer's website, and most others do the same as well.
here is a sample CD spectrometer picture of a compact florescent. the bright lines are where the color spectrum is peaking.

the spectrum is not standardized so sometimes you will see different graphs with colors in different positions, so for this DIY you should probobly compare your DIY readings against your other DIY readings instead of relying on the manufacturer's graphs. your DIY graphs will always be the "standard" though because they follow ROYGBIV... red orange yellow green blue indigo violet.