Laser safety glasses needed for unfocused beam?

[KronicKold]

I have a noob question that I'm hoping someone can answer.
I want to start out by saying that I understand safety glasses should be worn, I even have a few pair.

My question: is the danger the same with an unfocused beam? Or less dangerous ? More dangerous?

I ask because I am using a 20mW Sony 405 diode in a semi focused fashion. Using it as a csi style black light flashlight.

Next question: in laymans terms with no scientific calculations, can someone please explain the rating on the glasses, and what the minimum rating I would need at this power level. My pair are 5 OD. But they were $80. Other pairs are rated at 2 OD that cost $20, I saw a pair of 7 OD for $160.


Can anyone shed light on the price difference / value ?

 

[ARG]

Less dangerous with an unfocused beam. The danger is based on power density (W/cm^2) not power alone.

 

[Arayan]

Less dangerous with an unfocused beam. The danger is based on power density (W/cm^2) not power alone.

Do you know, approximately, the threshold between safe and unsafe value?

 

[ARG]

Do you know, approximately, the threshold between safe and unsafe value?

Around 1mW/cm^2

 

[Arayan]

Thanks, this is useful to know