Ah, now I understand. But this has no benefits. A LED that is continuously
on at, say 20mA, will appear to have the same brightness as when strobed
with a 20% duty-cycle (1/5 of the time) at 100mA (5 times the current).

Meindert
[/i][/color]


Actually not quite. If you talk energy consumption then you are right.
But you can viciously overdrivve LEDs to get far more brightness out
of then than they normally can give.

There is also argument that your eye and brain think that the led is
still alight and this can fool you into seeing a brighter LED. I would
reckon this would work best for LEDs being looked _at_, rather than
thiose used as a source of illumination.[/i][/color][/quote]



I have been designing such pulse driven led lights commercialy for over seven years. I have designed and made (still make) all the various LED navigation lights, including anchor lights, and cabin lights too, but some of the cabin models are not pulsed...pulse drive works better for *visibility*.

Yes, pulsing can increase PERCIEVED brightness, if the correct paremeters are followed, it is a well documented human perception phenomena. You don't really need to "overdrive" the leds either, just stay within their temp/current ratings for a given duty cycle. The led driver I use now takes into account input voltage, temperature, and type of led used, and without ever pushing more current through the led than it was designed to handle it produces a pulse train of a frequency, output voltage, and duty cycle such that from a very low voltage to a very high voltage (input) the led will be at a relatively uniform percieved brightness for a power consumption of about 60% of that required to get similar percieved brightness from continusly driven leds. Pulse driving with a carefully controled variable pulse is by far the most efficient way to get maximum percieved brightness, as not only do you utilize the inherently efficient design of switching control (either on or off, no wasting of electricity by turning it into heat) but you can take advantage of the perception factor and get a further boost in performance that makes this design concept superior.
The led nav light drivers I design also incorperate such features as transient, spike,and overvoltage protection, (I have tested the 12VDC light on 115VAC, it shrugged it off) day sensing, bi-polar operation, ect. into retrofit-able led 'bulbs', with the result that when used in a standard fixture they give the same or often even better visibility than the normal incandesecent bulb that they are designed to replace, IE greater than 2NM visibility, but with better functonality, features, and reliability. In fact, they are about as bright as other newer model led anchor lights that use a DC-DC converter to drive their leds, but the pulsed model uses only a small portion of the power that the DC-DC model does. I have reasonably good pictures taken at night with a digital camera that show pretty close to what the eye sees, comparing anchor light fixtures containing both incandesecent bulbs and continuously on leds with the pulsed model that bear this out.
A normal boat could anchor, turn the anchor light on, go away for the summer, and come back and start the engine in the late fall with no worries.

If anybody would like more information about led boat lighting design, I would be happy to send some to them off-list...it is kinda long. I can get carried away. ;-) -Ken