Re: LED efficiency

On Thu, 21 Jun 2007 21:16:20 +0300, "Ioannis"
<morpheus@xxxxxxxxxxxx> wrote:

Usually, when we talk about the efficiency of a light source being x lm/W for
example, I understand that every Watt of input power generates approximately x
lumens.

These lumens are of course energy and can be converted back to power, so the
overall efficiency of the light source can be determined as the ratio (light
energy)/(input energy)

The remainder in conventional light sources, is usually wasted as heat.

What is this difference wasted as in LEDs? Is it also heat?

In other words, if I manage to build a 400W LED arrangement with LEDs which have
efficiency 20 lm/W and if I have a 400W metal halide which has an efficiency of
90 lm/W, which will generate more heat?

Thanks much in advance,

As others have said, almost all the electrical power drawn
by an LED that does not go into light ends up as heat.

Based on your example, your 20 lm/W, 400-watt, LED system
will generate more heat than your 90 lm/W 400-watt, metal
halide system. The 20 lm/W, 400-watt LED system would
generate about 375 watts of waste heat, while the 90 lm/W,
400-watt metal halide system would generate about 290 watts
of waste heat.

To make matters worse (for the LEDs) the metal halide lamp
radiates a significant fraction of its waste heat away,
while the LED must rely on conduction and convection, AND
(as Don stated) the LED is far less tolerant to high
temperature than the metal halide lamp, so the fixture
designer must make sure this waste heat is removed in such a
way that the LED temperature does not get too high.

--
Vic Roberts
http://www.RobertsResearchInc.com
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