mercury is what provides the initial ions for current to flow across the
tube. it helps establish the arc.
I took apart a CFL and it only had two transistors,a tiny transformer,a
couple of electrolytic caps,2 diodes and some chip caps. It rectifies and
DOUBLES the input voltage,then converts to HF AC.
Next time one of mine burns out, I'll take it apart. The diagram I saw
looked complex for a light bulb. Sounds like what Wiki says:
Electronic ballasts contain a small circuit board with rectifiers, a
filter capacitor and usually two switching transistors connected as a
high-frequency resonant series DC to AC inverter. The resulting high
frequency, around 40 kHz or higher, is applied to the lamp tube.
Also noted of late, cfl's I've bought have been little hummers. Can't
recall in early ones. Maybe it's the cheap Walmart stuff I bought.
Like other fluorescents, the mercury is mostly liquid when the tube is
off. Starts on something more like argon. Heat from running vaporizes
the mercury (which is why they may not be full brightness at start). The
mercury arc produces a lot of UV, which the phosphors convert to visible
Other than the orange neon color ones, "neon" lights work the same, with
cold (not heated) cathodes.
Switch mode power supplies, like in a computer, seem to be winding up
According to the above link, this LED bulb consumes 8.6 watts to
produce 429 lumens (49.9 lumens/watt).
That is not much less efficient than a 40W-equiv. CFL, which produces
450-500 lumens from 9 watts (50-55.5 lumens/watt).
As for why this LED achieves about 50 lumens/watt while there are now
LEDs achieving 100-120 lumens/watt: I doubt the reason is filters:
1: My guess is that this LED bulb is a warm white one rather than a
cool white one. Warm white LEDs produce less green spectral content
and more red spectral content than cool white ones do. Not only is
human vision less sensitive to red than to green, but also phosphors
have higher "Stoke's loss" in producing red than in producing green
light from the same LED chip.
2: The LEDs in this bulb may be high color rendering index ones. There
is a recent trend for "warm white" LEDs used in lighting to have
color rendering index of at least 80. Cool white LEDs of extremely
high efficiency have CRI only 70 to low 70's, with some having
extreme lumen/watt phosphors only achieving CRI in the 60's.
Higher CRI requires the phosphor's spectral band to be wider,
to include a fair share of wavelengths from slightly bluish green
to mid-red. This is as opposed to a narrower phosphor band
concentrating on wavelengths from slightly yellowish green to
slightly orangish red. The wider band has more spectral content
at deeper red wavelengths that human vision is less sensitive to,
resulting in less lumens per watt.
3: The LEDs in this bulb may be less efficient than the most efficient
ones available of a given color and color rendering index. The
most efficient available LEDs have higher cost.
4: The LEDs in the LED bulb require a "ballast" or "driver circuit",
for similar reasons to the ones why a CFL requires a ballast
(included in usual screw-base CFLs). The ballast has some loss.
When a 120V AC-powered "LED driver" has 91 or 92% efficiency, that
is getting to be something to boast about. Merely fullwave-
rectifying 120 volts AC to DC has a loss around 1.5%.
- Don Klipstein ( firstname.lastname@example.org)
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