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random notes about fluorescent lights
I recently took a course on efficient lighting taught by someone from
the Lighting Design Lab in Seattle and I thought I'd share some of the
points that might interest you. Although the class covered various
technologies, I'll just cover fluorescent lighting since that appears to
be what most people are interested in.
In the 1970's, the first electronic ballasts appeared.
In the 1980's, compact fluorescents and T8s appeared.
Lamp life and lumen depreciation:
Lamp life is the average or median operational life. e.g., in a sample
of 100 lamps, by the time their total operating hours equals their
operational life, 50 will be burned out.
Lumen depreciation is the fractional loss of lumens at rated operating
conditions that progressively occurs during lamp operation.
At 100% of rated lamp life -
Halogen incandescents have about 95% of their initial lumens
T8 fluorescents (1", or 8/8ths of an inch diameter) - 90% (GEs new
Starcoat lamps (F32 T8) are supposed to maintain 95% of their initial
Incandescents - 80%
T12 fluorescents (1 1/2", or 12/8ths of an inch diameter) - 75%
Ballast types (these comments apply only to elec. ballasts for
Magnetic ballasts operate with an output (the elec. going to the lamps)
of about 60 Hz.
Electronic ballasts operate at over 25 kHz. People may notice the
flicker of magnetic ballasts, but not of the electronic ballasts.
Electronic ballasts usually run cooler than magnetic ballasts.
Ballast factor - the lumen output of the lamp and ballast combination
compared to the rated output of the lamp on an ANSI reference ballast.
Wattage consumed by the combination is approx. proportional to the
--Magnetic ballasts - .94 to .95
--Electronic ballast - .65 to 1.28
Note: lamp life may be reduced with ballast factors greater than 1.18.
Rapid start or instant start ballasts.
Instant start ballasts put more stress on the lamp when it's started,
therefore slightly reducing lamp life, but they also use less
electricity. However, at about 12 or more hours of operation per start,
lamps on instant start ballasts have about the same lamp life as those
on rapid start ballasts.
Energy consumption examples (unfortunately I don't know if these are for
instant or rapid start, but I'm guessing rapid start):
A .94 ballast factor mag. ballast running 2, 40W T12 cool white
fluorescent lamps will put out about 3050 rated lumens (2867 at .94
ballast factor) per lamp and use 96 watts.
A .88 ballast factor elec. ballast running 2, 32W T8 lamps (unknown lamp
type) will put out about 2900 rated lumens (2552 at .88 ballast factor)
per lamp and use 62 watts. This is about 11% lower lumens and about 35%
(A .87 ballast factor mag. ballast running 34W T12 energy saver cool
white lamps would put out 2750 rated lumens per lamp at 82 watts).
I hope you find this helpful or at least interesting.