Re: How do you make a shadow wall?

Hello Ricky – you wanted to know how to make a “shadow wall”. The quick 
answer is to go out and buy a pot of phosphorescent paint and a brush, and 
paint your wall. But your wall has to be in the right place…

The effect you are referring to is where the wall in question is kept in 
the dark or in very dim light so that when you shine a bright light on it, 
it shows the phosphoresence by absorbing the light, and then re-emitting 
light of another colour. I’ll briefly explain phosphorescence in a moment. 
Some shadow walls use paint, some use a layer of plastic – vinyl – in 
which phosphorescent pigment particles are dispersed. The effect is the 
same. After the strobe goes off, the wall glows where the light struck it, 
but not where it was shaded – i.e. by your shadow.
Hence an image of your shadow stays on the wall for a while. It does fade, 
of course, as the energy of the phosphorescence gradually dies away. Now 
you can see why the wall has to be kept in dim lighting – because 
otherwise two problems would prevent you seeing the effect. One would be 
that the bright ambient light would cause all of the wall to be glowing 
and your shadow would not show up unless you stood there for quite a 
while – so that the shaded part began to fade in phosphorescence. The 
second reason is because in bright light you just would not see the 
phosphorescence – because it is relatively low intensity and would be 
overwhelmed by the reflection of the ambient light from the wall..

Here is the definition of phosphorescence – and you can look this up and a 
lot more stuff about it at britannica.com:

Here is the URL:
britannica

Phosphorescence is the emission of light from a substance exposed to 
radiation and persisting as an afterglow after the exciting radiation has 
been removed. Unlike fluorescence, in which the absorbed light is 
spontaneously emitted about one hundred millionth of a second after 
excitation, phosphorescence requires additional excitation to produce 
radiation and may last from about one thousandth of a second to days or 
years, depending on the circumstances.

Great question, Ricky - keep asking them.