From: Winfield Hill
Subject: Re: What is maximum current for LED?
Date: 3 Oct 2002 09:34:45 -0700
Organization: Rowland Institute
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"Spehro Pefhany" wrote...
> The renowned Wouter van Ooijen (www.voti.nl) wrote:
>> So, in an attempt to kill a urban legend (which is, of course,
>> impossible): - for *signaling* it is a good idea to flash a LED
>> (optimal frequency? optimal P/P?)
> I'm not sure there is an optimal frequency/duty cycle. It's easy to
> miss very slow flashes. I suspect that a few Hz with perhaps 70% on
> time would be optimal when it's important to pick it up fast. Maybe
> Win can dredge some ballpark numbers out of his head?
My guess is that for an attention alarm, the main issues may be
things like irritance level (a flashing light can be a pain),
response latency (flash when within your angle of vision?), etc.
As for psychophysics issues, I think even just a single flash
gets optimal sensitivity; our extra processing for peripheral
vision no doubt resulted from ancient animals with this feature
surviving those who didn't have it - a single glint caught by
the corner of the eye being enough to invoke a startle response,
saving the animal's life. In modern terms, the capability is
critical when attempting to cross the Cambridge street in front
of the Institute, given a Massachusetts driver's propensity to
speed up when they see a pedestrian in the road ahead of them.