On Thursday, December 31, 2015 at 7:30:44 PM UTC-8, Doug Miller wrote:
Alas, that's not literally true; no LED is 50% efficient, because the light can come out of the
chip, or go the other way (and get absorbed). Fluorescent tubes could conceivably win
the efficiency battle some day (because they don't have to include opaque parts).
Not true. LEDs don't absorb 50% of their generated light. In fact
the direction of the beam is quite small. Diffusers are used (which
do absorb some light) to make the light more omnidirectional. It's no
problem to get LEDs that are twice as efficient (measured as getting
twice the lumens per watt) as a fluorescent.
On Friday, January 1, 2016 at 6:35:35 AM UTC-8, krw wrote:
Irrelevant, of course; the light is not formed as a beam inside the bulk of semiconductor,
but at glued-on lenses. That's only AFTER the light escapes from the solid semiconductor chip.
You'd have to count up all the quantum jumps that produce a photon, and note that
less photons than that are seen to light up the room.
No, it's not irrelevant. There is no rear beam to be absorbed by the
emitter. Thats just wrong. THe beam is quite narrow and
unidirectional. You do *NOT* lose half the energy immediately as can
be easily seen from efficiency numbers.
Since Watts are a measure of power and is related to Joules and
calories, I would suspect that a 60 watt LED would produce the same heat
as a 60 watt tungsten. (For give me if it is no quite right but it has
been 50 years since I did this sort of thing)
However I believe LEDs are compared to Tungsten by the lumens they
produce (amount of light) and a when you are talking LED you are
actually saying they produce the light equivalent to a 60 watt tungsten
bulb, not the LED is 60 watts.
Yes and no. Since the LED is more efficient, more of the power will
go into light (thus less into heat). The light is eventually turned
into heat, so yes, in the long run, the heat output is the same but
less heat will be dissipated in the fixture.
Yes, the LED would be "60 watt equivalent", or some such. It'll also
state the actual wattage but it will be significantly less. Depending
on the particular LED, this can vary a lot.
The problem is that LEDs are semiconductor devices so can't tolerate
much heat. Every 10C rise in heat will probably reduce its life by
2.5x (or perhaps even more).
You probably are not going to find a 60 watt LED, it would probably be
brighter than the sun. LED's marked 60 watt equivalent are just that,
equivalent. A 12-14 watt LED is equivalent in brightness to a 60-70 watt
incandescent. And FWIW a 15 watt LED bulb hardly feels warm even when
left on 24/7. The same said about a 15 watt incandescent will burn you if
you touch it.
LED's are 'effective' watts. They compare the light output vs a
standard and mark the bulb. The better LED's have several die that
send different color to be more like daylight. Some are warm.
On 12/31/2015 9:28 PM, Keith Nuttle wrote:
Don't count on it. LEDs (and CFLs, for that matter) need to be kept
much cooler than incandescent bulbs. Overheating the bulb will
*greatly* shorten its life. The issue becomes the bulb, not the
Right - in the bathroom the fan unit wants a 40. And make it darker
than without the light almost. I put in a 60w LED (effective) and it is
a 16 heat watt unit. Runs cool and won't melt the plastic. Shows more
light and my beloved loves it. No brainier on that one.
On 12/31/2015 7:01 PM, Bill wrote:
They're still running in the $5-10 neighborhood here, so maybe the power
company was investing some of your hard earned money in making the bulbs
appear cheaper to you. Ours did that with the CFLs, we stocked up at
something like 4 for 99 cents. Almost wish we didn't, as LEDs are so much
better, but they're still not cheap yet.
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