davidgdg
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Re: Laser Radiation Bioeffects
Forgot to check the dates. Sorry!
Forgot to check the dates. Sorry!
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ArcticMyst Security by Avery
- Joined
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Re: Laser Radiation Bioeffects
Guys --
Listen to Senkat and Frothy ----
The sun is not a point source of coherent light. Apples and oranges here
Protect at least one of your eyes.
Mike
Guys --
Listen to Senkat and Frothy ----
The sun is not a point source of coherent light. Apples and oranges here
Protect at least one of your eyes.Mike
Re: Laser Radiation Bioeffects
Perhaps more to the point: sunlight is divergent.
Collimated light entering the pupil will be focused at the retina.
Divergent light entering the pupil will be focused behind the retina.
Convergent light entering the pupil will be focused in front of the retina.
A laser is usually close enough to a collimated beam that the difference is academic when it comes to eye injury. The variation in the eye itself is going to make a larger difference. But a flashlight, the sun, or just about any other spatially incoherent light source, will tend to be divergent, so the area it hits on the retina will be a lot larger than for a collimated beam. Similarly, a convergent beam is going to be at its tightest in the aquaeous humor, which is how they nuke floaters, a procedure that still carries a 4% risk of permanent loss of macular vision in that eye, due to the power level involved.
For those that read the quoted passage as 105x amplification, that is due to a copy-paste problem. The original text states 10[sup]5[/sup], but the superscript isn't pasted correctly. And 10[sup]5[/sup] is 100000x, so the figure is correct: a collimated beam of 1mW/cm² will have a power level of 100W/cm² at the retina. Accordingly, when a BR laser is putting out 100mW in a 5mmØ collimated beam (20mm²), the density of optic power is 5mW/mm², which translates into 500W/mm² at the retina.
Clearly, nobody in their right mind wants to risk 500W/mm² of near-UVA to the retina.
OD3 brings that down to 0.5W/mm².
Perhaps more to the point: sunlight is divergent.
Collimated light entering the pupil will be focused at the retina.
Divergent light entering the pupil will be focused behind the retina.
Convergent light entering the pupil will be focused in front of the retina.
A laser is usually close enough to a collimated beam that the difference is academic when it comes to eye injury. The variation in the eye itself is going to make a larger difference. But a flashlight, the sun, or just about any other spatially incoherent light source, will tend to be divergent, so the area it hits on the retina will be a lot larger than for a collimated beam. Similarly, a convergent beam is going to be at its tightest in the aquaeous humor, which is how they nuke floaters, a procedure that still carries a 4% risk of permanent loss of macular vision in that eye, due to the power level involved.
For those that read the quoted passage as 105x amplification, that is due to a copy-paste problem. The original text states 10[sup]5[/sup], but the superscript isn't pasted correctly. And 10[sup]5[/sup] is 100000x, so the figure is correct: a collimated beam of 1mW/cm² will have a power level of 100W/cm² at the retina. Accordingly, when a BR laser is putting out 100mW in a 5mmØ collimated beam (20mm²), the density of optic power is 5mW/mm², which translates into 500W/mm² at the retina.
Clearly, nobody in their right mind wants to risk 500W/mm² of near-UVA to the retina.
OD3 brings that down to 0.5W/mm².
