Re: Excuse me Sir, can you see the laser beam?

The visibility threshold is a highly variable thing to determine.
The problem is the surrounding light as well as the adaption of the eye to
that surrounding light.
I'll note that 40% reflection is quite low and aluminum coatings are more in
the range of over 90%.

--
Bob May
Losing weight is easy!  If you ever want to lose weight, eat and drink less.
Works  evevery time it is tried!