Why some books write light itself is invisible but makes things visible for us. I mean if a laser beam is passing just parallel to our eyes in a dust free environment we can't see it but the reason for this is that position of our eyes was such that no amount of light got a chance to enter our eyes. Even if a table is lying at our backside in such a situation no reflected light from the table gets a chance to enter our eyes and it is invisible for us. The above mentioned laser beam becomes visible once chance is given to some portion of light to enter our eyes whether by allowing laser beam to undergo reflection or scattering or refraction. Now my doubt is why do we say light tself is invisible although we actually are not giving a proper chance to light to enter our eyes?

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    $\begingroup$ Can you provide sources for your claim? I have not read those books. $\endgroup$ Commented Mar 22, 2023 at 7:36
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    $\begingroup$ Another way to define visibility is that it scatters light. From linearity of Maxwell’s equation light does not scatter light so is invisible. However, at high enough energy, you can have light light scattering according to QED. A starting point would be: “Do photons cast shadows?” $\endgroup$
    – LPZ
    Commented Mar 22, 2023 at 7:47

1 Answer 1


This is not really a question about physics, but a language issue. Define "visible".

An object emits light, and you (as an observer) detect the light with your eyes.

  • If "visible" applies to the object, then you can say the object is visible, by definition. By this definition as well, light is not visible, because light itself does not emit light. You might oppose that a laser beam is visible when it passes through dust, but you see the dust, not the light.

  • If "visible" means something that your eye can detect, then the light is visible. By that definition, the object itself is not detected by your eye, so it can be considered invisible.

Anyways, my point is that the question is simply about imprecise language.

  • $\begingroup$ Thanks really it is something which is related to what we mean by being visible $\endgroup$
    – Shinnaaan
    Commented Mar 22, 2023 at 14:57

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