Originally Posted by
shobley
Are there goggles that reduce the laser emission, but do not eliminate it?
Short answer... Yes
You need to look at the Optical Density (OD) of the goggles. The higher the OD the more light is blocked. It can be quite a challenge deciding which OD is correct for each particular application. Too high an OD is just as bad as too little, if the OD is too high and you cannot see any of the emission there's always a temptation to lift the goggles just to have a quick peek to see if it really is working
Likewise if the OD is not high enough you run the risk of getting eye damage from a stray 'flash'.
Basically, it's your call
Laser safety eyewear is usually labeled with both the optical density and the wavelength coverage range.
The formula for optical density is ...
Optical Density = -1 (Light Transmission)
Tl = 10 -OD
Using the formula above you can see that there is a 10x increase in protection (10x decreases in laser transmission) for each increase in OD.
Jem
P.S. Just found this slightly better explanation on Wikipedia...
In optics, density is a unitless measure of the transmittance of an optical element for a given length and wavelength λ:[1]
O = the per-unit opacity
T = the per-unit transmittance
I0 = the intensity of the incident light beam
I = the intensity of the transmitted light beam
The higher the optical density, the lower the transmittance.
Defined in terms of unit length, and expressed in decibels, the density is termed the transmission loss rate For example, an optical density of 0.3 corresponds to a transmission loss of 3 dB per cm. Defined without regard to the length of the sample, the density is a synonym for absorbance. Neutral density filters are typically quantified this way. Some filters, notably welding glass, are rated by shade number, which is 7/3 times the optical density. A shade number of 14 is regarded as safe for direct observation of the sun.
Last edited by Jem; 04-24-2008 at 06:47.
Reason: Wikipedia information
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