• Question: What would happen if you would point a laser pointer through lots of lens would it make it more dangerous?

    Asked by geantlebu to Tim, Wallace, Steve, Sarah, Peter, Paul, Mousumi, Mina, Linda, Fi, Danielle, Benjamin, Ben, Andy on 30 Dec 2014.
    • Photo: Tim Stephens

      Tim Stephens answered on 30 Dec 2014:


      The harmfulness of a laser is not based on how many lenses it is shone through. When you’re calculating how to classify a laser hazard, there’s only one lens that matters, and that is the one in your eye. You use information about the laser to work out the maximum amount of energy that can reach the retina at the back of the eye and then check to see whether that amount of light will cause harm.

      Laser pointers that you can buy legally in the UK should all be completely safe, and there’s nothing that can be done to make them more dangerous.

    • Photo: Paul Murcutt

      Paul Murcutt answered on 30 Dec 2014:


      The trick here is that the light in a laser is all travelling in the exact same direction already.

      With lenses you usually focus light that is travelling in different directions onto one point. With a laser that is fairly pointless.

    • Photo: Fiona Dickinson

      Fiona Dickinson answered on 5 Jan 2015:


      Laser light is what is called collimated (all going in a straight line), which means if you point it at a wall from up close or far away the dot should be the same size. Due to imperfections this isn’t always perfectly the case but the idea stands. Lenses focus light, and will take a laser beam and focus it onto a point (this is important for my research), but after the focal point it becomes more diffuse.

      To me, shining a laser pointer through lenses does make it more dangerous, but not for the reason I think you will be expecting. When light hits an object some of that light is reflected, this reflected light is now my concern, it is still largely collimated, but is now going in another direction. You have to take care not to look directly at this reflected or scattered beam just the same as the original beam.

      This scattering of laser light is why I never wear and rings or a watch when I am using the lasers in the lab.

      One thing I will say is all lasers are dangerous, never look directly at laser light, always check your laser pointer is Class 2 (especially if using it with pets) and never shine it at people.

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