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I can't remember what is the word for those funny light spots created when you take a mirror or any reflecting surface and make a spot of light that can be moved all over the room, walls, etc. Does anyone know?

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In my family (rural Australia) we have always used the term "jack-a-dandy". I can trace this back to a usage in 19th C London (sorry, reference escapes me - not my family, though.) It was an article on children's games. One boy complained that another had cast a jack-a-dandy in his eye with a mirror or similar. The trail stops there. I tracked down an earlier (?) English saying to the effect that, on a day when sun and rain alternated rapidly, "Jack-a-dandy is beating his wife with his golden stick". In Germany, in the same circumstances, it is the devil who is beating his wife. My Jamaican sister-in-law reports a similar saying in Jamaica.

Reference added:

Jack-a-dandy -- Wiktionary

(noun) 2. (New Zealand) A small patch of light reflected from a shiny surface onto another surface such as a wall or ceiling.

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My Dad used to say "icky more, icky more, shinning on the kitchen door". I assumed everyone use to say that, but I now realise that everyone has their own names for them.

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The specific optical effect you are after is:

Caustics

In optics, a caustic is the envelope of light rays reflected or refracted by a curved surface or object, or the projection of that envelope of rays on another surface.

Note, that even very slightly curved surfaces such as a the glass on a watch can (and do) cause caustic reflections.

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Reflections:

the act of reflecting, as in casting back a light or heat, mirroring, or giving back or showing an image; the state of being reflected in this way.

(Dictionary.com)

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  • Wow, great, thanks for the answers! We have a phrase for this is Bulgarian 'sun bunny' and I couldn't escape the feeling that there is something similar in English. Obviously there is not :) Thanks!
    – Theo
    Commented Aug 25, 2016 at 13:25
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    @Theo Not common in English, but in my family we called the singular reflection cast by sunlight bouncing off my father's wristwatch onto the car's interior during long boring car rides "the peanut" (due to the oblong shape created by a circular reflection hitting a surface at an angle). He used to move it around and create stories about it to amuse us and ameliorate the boredom.
    – Dan Bron
    Commented Sep 24, 2016 at 13:37

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