So You Think You Can Safety Google.

**mixedgas** · 07-21-2009, 17:54

Posted at the request of a friend.

OPTICAL DENSITY = -LOG TRANSMISSION

SO, example, You have a 300 mW single line laser.

You aim it into your proposed goggle material

with something sensitive and accurate like a coherent Power Pen
you measure 30 microwatts which is .030 milliwatts.

So first you need to calculate the transmission.

T= .030 milliwatts/300 milliwatts = .0001 ie T =10-4 in scientific notation

OD = - log T

then OD = -LOG 10-4 (on a cheap calculator it would be log .0001)
which will read out as -4

OD = -(-4)

OD = 4

OD = 4 means that the beam is 1/10,000 of the input power when it comes through the goggles at the wavelength they are designed for

OD = 6 means that the beam is 1/1,000,000 of the input power when it comes through the goggles at the wavelength they are designed for ie one millionth.

Thus endeth the lesson.

Steve