Re: efficacy of LED's

In <1150576553.151718.138790@xxxxxxxxxxxxxxxxxxxxxxxxxxx>, redbelly wrote:

Victor Roberts wrote:
On 17 Jun 2006 08:22:21 -0700, "redbelly"
<redbelly98@xxxxxxxxx> wrote:

You need current regulation for an LED, which brings down the overall
efficacy. Not required for incandescents or cfl+ballast.

If, for example, a 20 lm/W LED becomes 15 lm/W after adding a current
regulator, then it doesn't beat a household incandescent bulb (15
lm/W).

You're assuming a current regulator with an efficiency of
only 75%. There is no reason why a good LED current
regulator cannot have an efficiency of 90% or more, which is
similar to that of high quality electronic ballasts.

The ones I've seen have roughly a 1V drop. If you run a single white
LED (3.5 V) with that, that gives a 78% efficiency. Do you know of
regulators with smaller voltage drops, or are you thinking in terms of
running strings of LED's on a single regulator?

I know of such circuits having voltage drop more like half a volt.
Consider inductive switching ones using power MOSFETs and "catch diodes"
being Schottky diodes. Along with the obvious design parameter of higher
battery voltages.

I would say that 85% efficiency of "an LED ballast" is low end of
someone trying to work at that and shaving costs by so severely as 1/10ths
of a cent, and 90% is fairly easily achievable without great cost.

- Don Klipstein (don@xxxxxxxxx)
.

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