Luxeon III at 350ma?

If I was to make a light with a dimmer switch to save battery life, is a Luxeon III running at 350ma going to put out the same amount of light as a regular one watt? Would the color be different? (Given the same bin)

At 350mA a Lux 3 will behave about the same as a 1W at 350mA. Of course the colour & Vf will be bin specific. By just dropping the current rather than doing PWM at a fixed current the colour temperature will change a bit - though won't be an issue for most applications.

How are you going to switch to different current levels? You mention a dimmer switch - if you plan just switching in some resistors in series with the Luxeon then you really won't be saving much in terms of battery power...

george.

Sure he'll be saving battery power. If he goes from 700mA to 350mA, the batteries will last twice as long, no? It'll just be less efficient.

It should be more efficient to change resistance - just not as efficient as a regulated setup with PWM. Current drops with more resistance, but you drop more voltage across the resistor. If you're not careful about resistor/pot setup, you could turn that pot into an on/off switch of sorts if it eats up all the voltage.

Yeah, I just plan on doing it with resistors. Thanks guys...

What I meant by not saving much, was that a lot of runtime will be wasted by dropping voltage across the resistor 'if' the input voltage isn't relatively close to the Luxeon Vf. Another question for you - what is the power source (cell type & number of cells)?

I guess I'm biased, I've always designed & used switchers to run my Luxeons - all current regulated. Then I just varied the current or varied the duty cycle via PWM to provide dimming.

george.

George is right about PWM being more efficient, but one should not underestimate the runtime gains from simply limiting the current with a resistor. I've gotten more than 24 hours of usable low level light from an ARC LSH-P with it's current limited to 30 ma by a resistor.

In designing new boards, changing the pulse width (PWM) is definitely the way to go. In retrofitting existing lights, a resistor may provide sufficient benefit without replacing the electronics of the light.

But I may be prejudiced in the matter; /ubbthreads/images/graemlins/smile.gif I'm still selling the hi/low spring assemblies for ARCs and similar lights.

Daniel