# Help with Laser MPE calculation

I am building a laser room and I'm basically trying to calculate the maximum time of laser radiation to they eye before causing any harm. I found that to be 7 seconds but I would very much appreciate if someone familiar with this topic can confirm that my calculations are accurate.

The lasers I use are green ones @352nm 50mW. Based on the MPE and coefficient tables, the formula for Hmpe = C1 J/m^2 = 5.6 x 10^3 x (t^0.25) J/m^2 = 5.6 x 10^3 x (7^0.25) J/m^2 = 9.1 x 10^ 3 J/m^2

In terms of irradiance obtained after dividing by t = 7s:

Empe = 1.3 W/m^2

Now, from here "considering the limiting aperture of they eye in the visible region, 7mm, then the area over which the visible radiation will be viewed is π/4×0.7^2 = 0.385 cm2 = 3.85 * 10^-5 m^2 "

, the maximum power to avoid harm due to eye exposure is:

3.85 * 10^-5 * 1.2 * 10^3 W = 0.05W =50mW which is my lasers's output power.

You think this calculation is accurate?

Thank you in advance, Dimitris

• Don't mess around with your eyes, the best limit is 0 seconds... – Solar Mike Feb 7 '18 at 12:13
• I agree but I still need to calculate safety levels. Thanks – DimC Feb 7 '18 at 12:24
• Read the laser data sheet, take note what category of laser it is classified as and look up the safety precautions for that classification. – Andy aka Feb 7 '18 at 12:32
• Get a pair of safety glasses designed to block the wave length of your laser. – Tyler Feb 7 '18 at 13:11
• @Tyler, but what o.d. do they need? Not all laser safety goggles are alike, even blocking the same wavelength. – The Photon Feb 7 '18 at 16:03