Truth Goggles

‘Truth’ Goggles – Diffraction and Spectral Emission


Flourescent Light bulb, Tungsten (incandescent) Light Bulb, Diffraction Grating Glasses (you can buy them here), spectral lamps (optional), dimmer (optional),


Use the glasses to examine the difference between energy-saver light bulbs and incandescent ones. The incandescent bulbs should give a rainbow on either side of the light bulbs, the flourescent should give different coloured replicas of the light source itself. Try looking through them at an extension cord (white) on a dark background whilst wiggling it to see something really weird.


All objects above absolute zero produce some form of electromagteic radiation (light). Humans produce infrared light as we are ~ 37 degrees Centigrade. Objects the temperature of the sun (~6000 degrees centigrade on its surface) produce light in the visible range – or rather we have evolved to see the radiation given off by the sun. The hotter the source (control the incandescent light bulb with the dimmer) the more blue the rainbow appears – the cooler the source the more red the rainbow appears. Incidentally this is the same reason some stars appear blue (Rigel and the Pleiades/Matariki) and some appear red (Bettlegeuse) in the night sky.

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