Infrared Emissions from an Incandescent Bulb

Mar 2003

A simple qualitative experiment to use a digital camera (HP 618) to record infrared (IR) emissions from an old 12V automobile incandescent bulb using a stack of three Memorex Black CD-R discs as a primitive IR transmission/visual blocking filter.

A 1/15 second exposure with filter. The filament was positioned near the center of the discs where there is no coating. The violet object is the bulb's filament seen through the stack. The orange-red glow is light reflected from the white background through the center hole of the stack. To the eye the colour of the filament as seen through the stack was not violet but red, consistent with the CD-R blocking visible but passing IR and some red -- the violet being a false colour due to the way the camera records IR. The colour of the orange-red glow agrees with what was observed visually, so the camera's colour balance is OK.

A 1/15 second exposure without filter. The exposure overexposes the filament. The IR content probably assists with the overexposure. The colour of the orange-red glow agrees with what was observed visually, so the camera's colour balance is OK.

A 1/500 exposure without filter. It finally starts looking non-saturated and somewhat close to the visually observed colour of the filament, but is still not red enough. It's possible that the camera's colour balancing may have tried to make this look white.