Calibrating spectrometers – using solar spectrum as gold standard

I have described previously how I made or obtained calibration light sources using compact fluorescent bulbs, LEDs and RELCO starter bulbs – however in each case I need to be able to identify accurately which lines are present on the spectra from those light sources before I can effectively use them for calibrating my spectrometers.

For some – such as compact fluorescent bulbs – information on the main lines is accessible online.

However, the RELCO starter bulbs has turned out to be more difficult. I have managed to identify a few lines only so far:

First attempt at determing frequencies of lines on my spectrum of RELCO Glow starter lamp taken with Science Surplus DIY Spectrometer

In this post, I will describe my attempt to use to the solar spectrum to identify further lines in the RELCO starter spectrum.

The solar spectrum has well defined lines (Fraunhofer lines) and detailed information on these lines and their frequencies is readily accessible online. It is very easy to obtain a solar spectrum during the day by pointing a spectrometer at blue or even cloudy sky (do not point directly at the sun).

I have therefore had a go at preparing a typical solar spectrum in graphical format similar to that generated by my spectrometer software and labelling it with main Fraunhofer lines, in order to use this to help me determine what the wavelengths are of lines on my light sources.

The idea is that I can then use blue sky (I can do this easily during daytime) to obtain a solar spectrum with my spectrometers and then use same set up for obtaining a spectrum of the RELCO and LED light sources so that I can compare the two and use the graph below to determine the wavelengths.

Hopefully this will work!


The following will take you to what followed on from the above – my first attempt to calibrate my homemade REKCO starter based calibration light using the solar spectrum:

First attempt at calibrating RELCO starter spectrum against solar spectrum

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