Magnifying glasses

[stephen777]

Reading through these forums I have found a lot of people talking about the dangers of high power lasers and the need to use goggles. Yesterday a 1.8w laser module that I had bought from DTR came in the post and I used it to burn random stuff around the house, with good goggles of course. (I'm having suspected driver problems now with this laser but thats a different story.) Anyway, using this laser reminded me of when I was a bit younger using a magnifying glass to burn stuff. I did a few searches on here and saw some rather impressive estimates for the power of the spot produced using a magnifying glass and the sun. I remember using the magnifying glass to try and burn white paper and the massive after images this caused. Could this have produced any damage or is sunlight somehow different to a high power laser spot while burning? I don't have any noticeable eye damage btw...

 

[KrowBar]

There are certainly differences between the light from the sun and that from a laser, some of which tend to make the laser light more dangerous. On the other hand, looking at the sun hasn't ever been good for the eyes either. The main reason that your eyes aren't as likely to be damaged by looking at the high intensity image of the sun on a somewhat reflective surface produced by a magnifying glass is that the power density falls of rapidly with distance. The rays of light converge/diverge after passing through the lens, and are further scattered by the non-specular reflection off the surface you are viewing. Another attenuating factoris the non-coherent nature of sunlight which is spread across a broad range of wavelengths, and not "in phase" such that it isn't as likely to produce local interference pattern hotspots.

 

[stephen777]

Interesting, so even though looking at the spot from the sun can look much brighter, the laser is more dangerous. I guess there is also the fact that the human eye can't pick up some laser wavelengths very well which would make it even more dangerous. Good to know there isn't a very high chance of damaging your eyesight with a magnifying glass.