I purchased the following multi-coloured LED strip light from ebay – Ed at the last RAG meeting asked whether coloured LEDs could be used as a calibration light for spectrometry – it seemed like a good idea! This one comes with a neat little remote control to allow it to be placed some distance away (ideal for focusing a telescope on it and then turning on and off and changing colours).
I made a calibration light out of the strip light above and a piece of Perspex made to diffuse light (off ebay designed for light boxes). I could then take spectra using my CCDSPEC spectrometer:
The first three spectra show that red, green, and blue are all very pure colours from the relevant LEDs in the strip:
Spectrum of LED strip light – green LED (below):
Spectrum of LED strip light – red LED (below):
Spectrum of LED strip light – blue LED (below):
Producing multiple lines on a single spectrum:
The above graphs demonstrate that the LEDs individually produce pure colours. However, for calibration purposes, it is useful to be able to have multiple lines on a single spectrum. This is where this particular colour-changing LED strip is useful – the strip uses three different coloured LEDs as above but allows you to select various combinations of LEDs to produce variety of “colours” – each of this is a mixture of LEDs switched on together in varying amounts.
The following are three examples of combinations – there are a total of 16 colours available (16 combinations):
Spectra from the three examples of colour combinations:
X-projections from spectra from the three examples of colour combinations:
White colour on the LED strip:
Probably the most useful combination is when all three LEDs are turned on together “white” – donated by a convenient “W” button. The spectrum from this produces three convenient peaks for calibration (below):