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:
These are the bulbs, in the same order as the spectra above:
| From | Printed on bulb | Operating characteristics |
|---|---|---|
| Globe | Ultra Mini 13W 120V 60Hz 210mA China | Delayed start, then about 2 minutes to reach full brightness. Slightly orangey-yellow, reminiscent of sodium-vapour lighting. |
| EarthBrite | TP N0413M 13W 120V 60Hz 210mA China | Immediate start, immediately bright. |
| Philips | Marathon Mini Decorative Twister EL/mdT 15W 120V 60Hz 220mA E5 China | Immediate 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