Max no protection power?

[kivig]

Hi,
I'm going to build a "better" (original was intended as is) version of this:
Video

And I 'm trying to find a safe answer about what power 405nm laser can be that will be safe for viewers without any protection.
Of course, no one will be let to look into the laser (it will be unreachable), but are there limits on looking at spot lit by it?

Thanks!

 

[Sparkles]

Hi,
I'm going to build a "better" (original was intended as is) version of this:
Video

And I 'm trying to find a safe answer about what power 405nm laser can be that will be safe for viewers without any protection.
Of course, no one will be let to look into the laser (it will be unreachable), but are there limits on looking at spot lit by it?

Thanks!

It depends on the laser wavelength, surface reflectivity characteristics, and distance / (angle of beam) from the surface the people will be located. We would need a lot of info before giving a good answer. 50 mw green (532nm) is super bright for me on a surface and gives me a little bit of an after image at 10 ft. away.

 

[kivig]

It depends on the laser wavelength, surface reflectivity characteristics, and distance / (angle of beam) from the surface the people will be located. We would need a lot of info before giving a good answer. 50 mw green (532nm) is super bright for me on a surface and gives me a little bit of an after image at 10 ft. away.

Surface is a glossy PVC plastic with reflectance ratio of about white.
The beam is almost perpendicular to surface about 10m away.
People can be anywhere in between or behind laser, but the laser will be above the head level as will the receiving screen so no one should get direct or glossy reflected light.
Environment is very dark. About night in the wood dark.

 

[Coherent Light]

This <5mW

 

[Prototype]

It is strongly recommended to use safety goggles for anything >5mW.

 

[kivig]

It is strongly recommended to use safety goggles for anything >5mW.

Is it for protection against getting accidental beam in the eyes or for looking at projected spot?
It's just that in linked video I use about 5-20mw and there's no really noticeable "after-image".