[Cyborg] 200 laser diodes

Eric Boyd mrericboyd at yahoo.com
Sat Jun 5 18:21:51 UTC 2010

Mitch Altman wrote:
>  > I have an interesting safety question: do you think that PWM controlling
>  > the lasers would actually make them eye safe? For instance, let's say
>  > we discover that the true optical power of the lasers is something like
>  > 10mW. Would it actually make them any eye safer to PWM control a laser
>  > to 50% duty cycle? Theoretically that reduces the "power" to 5mW, but I
>  > expect that in practice it's the peak intensity on your fovea that
>  > causes the damage, and PWM will not reduce the peak intensity. Thoughts?
> PWM definitely can reduce the effective light output. But, will these
> laser diodes pulse at a high enough frequency to allow for PWM? We'll
> just have to try and see.

Actually, it's precisely the fast response of the lasers that I am 
worried about.  PWM can definitely control the average 
electrical/optical power, but my understanding it that is isn't 
necessarily the average that is dangerous.  If you had a 1W laser, but 
PWMed it to 5mW (so 0.5% duty cycle), I still wouldn't want to shine 
that in my eye, I think it would be hella dangerous, much more dangerous 
than a constant-strength 5mW laser.  It's the difference between a bed 
of nails and a nice mattress.  It gets more dangerous the slower the PWM 
is, of course.  So maybe the trick is that we need to PWM as fast as 
possible?  Arduino PWM is only like 500 Hz, which isn't very fast.


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