Thread: Strange problem with low energy light bulb
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Lostgallifreyan Lostgallifreyan is offline
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Default LEDs as lamp replacements
(Don Klipstein) wrote in
:

Ok, I see that lumens depend on the spectrum, not just the actual
visible watts emitted, but given that there is convection in an
incandescent lamp that makes some of its power emit in the IR, does
enough leave that way to bring the lumens per input watts down to
levels that can account for stated line-power-to-light efficiences of
3% and lower?

Most of the output of an incandescent is IR.


What I meant was, might more heat be carried away by the convection in the
argon fill, and be either conducted or radiated away at far longer
wavelengths? I mentioned convection specifically to be clear I'm not
talking about directly radiated energy.

I think when Cree talk of lumens per watt, they're talking of lumens
for each watt of electrical input, and that's how I want to make the
comparison.

I was only mentioning figures of lumens per watt of visible light
output
to explain that an incandescent achieving 17.1 lumens per input watt
is nearly 7% efficient.

Put 100 watts into an incandescent that chieves 17.1 lpw. You get
1710
lumens. Each lumen is about 1/250 watt of "white light", not the
1/683 watt assumed by those claiming incandescents are only 1-2%
efficient.


I've managed unintentionally to get you to say that three times now.

I'm not always quick on the uptake, but I try... what I'm getting at, is
can any other evaluation result in that lower figure? I'm not convinced
that taking only the lumens at 555 nm accounts for this. Lumens seem
slippery enough if they depend on spectra and photopic sensitivity anyway.

Wikipedia again:
"In photometry, luminous flux or luminous power is the measure of the
perceived power of light. It differs from radiant flux, the measure of the
total power of light emitted, in that luminous flux is adjusted to reflect
the varying sensitivity of the human eye to different wavelengths of
light."

I guess that much can be relied on. So try it this way:

Take a 100W incandescent, and a large ellipsoidal mirror to gather as much
of its radiant flux as you can, throwing it to the other focus of the
ellipse where a black painted thermopile awaits. The incoming light is
passed through a dichroic filter at 700 nm to send the IR elsewhere and
pass only the visible light to the thermopile. Assuming you get close to
ideal light gathering for the visible wavelengths (and IR rejection), how
many watts will be read from the thermopile?

I understand that photometric measurements abount, and radiometric ones are
rarer, but that's what I want to look at, as without that grounding the
rest seems most insecure.
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