From: Winfield Hill
Subject: Re: What is maximum current for LED?
Date: 3 Oct 2002 06:10:13 -0700
Organization: Rowland Institute
X-Newsreader: Direct Read News 2.98
"R. Lewis" wrote...
> "Winfield Hill" wrote
>> ... Alternately, if the LED's primary purpose is to
>> attract attention, peripheral as opposed to foveal viewing has
>> a much greater sensitivity to light variation, which means that
>> a greatly reduced level of flashing light can be noticed out of
>> the corner of one's eye, prompting further closeup examination.
> Is there *any* advantageous effect of pulsing leds with a high
> current like this? It appears that many 'tronics people believe
> that there is (or should be) some perceived enhancement but never
> manage to give either a plausible reason or an authoritative source
> for it being so.
I'm sorry, was I unclear? The retinal receptors in our peripheral
vision field are hard-wired to transient-processing circuitry, which
results in a greatly enhanced sensitivity to dim flickering sources
(in the 2 to 50Hz range) in our peripheral vision, as compared with
our foveal vision. This effect is so strong that, under the right
circumstances, one can detect something flickering peripherally and
yet be unable to see it when turning to directly examine the source.
This means that a flashing LED is a _much_ better warning indicator
than a steady illuminated one. That's a serious advantageous effect.
I probably have 30 appropriate references among the several thousand
in my vision-research collection (and I've viewed the effect myself,
unpublished (:-)), but with your permission, I won't look for one now.
As for pulsing the light so fast that it appears to be steadily on,
you are correct, this does not enhance the apparent brightness.