On Wed, 4 May 2005 07:21:24 -0400, you wrote:

>Denny Esterline wrote:
>> I'm no expert on IR links, but the ones I've used had much lower than
>> 50% duty cycles.
>> It seems to me, that if you used a shorter on time, it'd make the
>> looping and testing easier,
>> not to mention letting you drive the LED harder.
>
>Less than 50% duty cycle is often used in battery operated equipment to save
>power.  It does *not* allow you to get more range for the same power, in
>fact it is a little less efficient.  

But range in an IR system is mostly about peak, not avarage power, assuming the receiver has
reasonable frequency response, so shorter, more powerful pulses will give substantially more range. 
Shorter duty cycle also allows the LED to be run harder - many IR LED datasheets quote seperate
figures for avarage and peak currents.
IR remotes typically use duty cycles below 20%,  putting 100-500ma pulses into the LED.

IRDA is an extreme example, using very short duty cycles with high-bandwidth receivers to get
maximum range.

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