RFI isn't going to be a problem if the switch is close to the application.
You can use an LM3524, NE555 etc. to drive the gate of a MOSFET.

The tradeoff is between LED life and pulse current. See www.agilent.com for
pulsed LED application notes.

"Asimov" wrote in message
...
"Tom Coates" bravely wrote to "All" (12 Oct 05 19:28:03)
--- on the heady topic of "Pulsing LEDs for higher efficiency"

TC From: "Tom Coates"
TC Xref: core-easynews rec.radio.amateur.homebrew:88233

TC I want to build some emergency lighting equipment using LEDs and 12V.
TC A friend told me that it is possible to get more light per Watt by
TC pulsing the LED to instantaneous levels well above its average ratings.

TC Is this true, if you include power consumed in the pulsing circuit?

TC If it is, can anyone suggest a simple and cheap circuit and the
TC appropriate operating values?

TC The reason for the 12V requirement is that I'm also working on a solar
TC charger for my transceiver batteries and want to use the same charger
TC for the lighting batteries.

TC Suggestions would be appreciated.

TC Tom, N3IJ

This pulsed drive technique is supposed to take advantage of the human
vision's persistance. If the led is driven brighter for a long enough
time the eye will perceive it as being brighter than if using the
equivalent average continuous current. Visual persistance is
approximately 10 milli-seconds, and if the repetition rate is faster
than this then the led will seem to be on all the time. The same
technique is used with multiplexed digital displays.

One problem with pulsed led drive is that it generates rfi due to the
rapidly switching voltage levels. Unless care is taken with risetime,
wire lengths, decoupling, and shielding, then the gain in efficiency
is a doubtful tradeoff for the simplicity of direct dc drive. It
depends on the application. If you want really bright flashes then use
a xenon strobe tube.

A*s*i*m*o*v

.... Neurotoxin Lite! Tastes great... Less drooling...