Emission spectra of some compact fluorescent lamps (CFL bulbs)

Dec 2010 (orig Dec 2006)

Compact flourescent lamps (CFL) have colour casts and other peculiarities that unfortunately aren't described on their package at the store. To investigate their differences, I tried looking at the emission spectra of three bulbs I happen to have on-hand.

Here are the emission spectra of three CFL bulbs compared with a 60W incandescent bulb and an LED lamp, obtained using a diffraction grating and a 'narrow' slit:

bulb spectra

These are the bulbs, in the same order as the spectra above:

bulb photos

FromPrinted on bulbOperating characteristics
GlobeUltra Mini 13W 120V 60Hz 210mA ChinaDelayed start, then about 2 minutes to reach full brightness. Slightly orangey-yellow, reminiscent of sodium-vapour lighting.
EarthBriteTP N0413M 13W 120V 60Hz 210mA ChinaImmediate start, immediately bright.
PhilipsMarathon Mini Decorative Twister EL/mdT 15W 120V 60Hz 220mA E5 ChinaImmediate start, immediately bright. 'Cool', daylight colour.

All the CFL bulbs were steady (no perceived flicker).

It'd be nice if labelling for CFL bulbs would include the operating characteristics, emission spectrum chart and colour cast, and brightness.

Some CFLs are labelled with a 'temperature', in degrees Kelvin, but of course a continuous-spectrum black-body-radiation profile would be only a very rough approximation of the discontinuous spectra emitted by any of the CFL bulbs here. An emission chart would convey more information, or a 'colour rendering index' value, CRI.

References: Spectroscopy, fluorescent lamps

Jim Elder
Ottawa, Canada

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