> One disadvantage of using an IR laser is that if eye contact is
> possible, the allowable power limits for safety are effectively MUCH
> lower for IR than visible due to the lack of an eye blink reflex. The
> classification (3a) for laser pointers cannot be applied to IR lasers.
> Avarage power can be reduced by pulsing, but because of the way the
> standards are written, avarage power must be calculated over a fixed
> 10 second period.

Thank you, that's good to know. I was aware of the blink reflex, but
not the IR limits. I'll have to look into that. Red can be set up visually,
IR will have to be done with a camera. Still undecided until I find out
which is going to be the most effective in daylight - eg will the day
light filter on most detectors cut more red or IR, and will red or IR
stay focused further

> From memory when I was last involved in this, the
> limit for class I classification of a 780mM IR laser came out to be
> something like one  50mS  1mW pulse every 10 seconds (it's the
> product of the length and power that matters, so for example fifty
> 1mS pulses would be the same).

That would apply to a spot wouldn't it ? If there's a line then the power
will be spread out. Assuming 100% lens efficiency, a 5mm round spot
has thinned out (at 10m, 120 degrees arc) to a 200,000mm x 5mm
spot or 1/40,000th. That sounds incredibly watered down, but the line
I made with a piece of perspex rod was perfectly visible at 10m, just a
bit tatty. To state the obvious, a laser does have an amazing amount of
illuminating power. So, firstly you have the attenuation due to the lens,
which will always be in front of the laser, and secondly the ID pulsing,
which further weakens the average power. I think I may be OK, even
with more than 1mW source

> For IR, anything over the Class I limit becomes a pain for product
> compliance due to eye protection requirements.

Wouldn't think of putting even a camera to the laser printer module
I played with - Class 3

> If the laser cannot come into direct eye contact this is not a problem
> until you get to more scary power levels.

As above, the lens will spread the power. The only time there could be
a problem is if a person gets so close to the lens that the light dispersal
is not yet great enough. The source will more than likely be at least 6ft
high, so that's only a remote possibility, and never say "can't happen".
If the source is mounted down a horn then somebody would have to
be pretty determined to stick their beak down there and do themselves
damage

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