THanks to jdurg:
It's pretty simple. You need to have fairly concentrated Hydrogen Peroxide (H2O2) with some concentrated ammonia solution mixed in. Do this very carefully to ensure there's no rapid decomposition of the H2O2.
Put this mixture into a tall graduated cylinder. In a separate flask with a one-holed stopper, put some concentrated calcium hypochlorite solution and slowly add concentrated HCl to it. This will start generating chlorine gas. The stopper should have a glass tube coming out of it with the other end under the surface of the H2O2/NH3 mixture. Once you've got the HCl added, put the stopper on.
The Cl2 generator should be setup at a higher level than the graduated cylinder as Cl2 is much denser than air so this will cause it to flow out the glass tube into the H2O2/NH3 cylinder. As the chlorine enters the graduated cylinder, it will cause the decomposition of the H2O2 and it will form exicted (singlet) oxygen which will glow red.
Just make sure this is done in a well ventilated area as the Cl2 and NH3 are pretty nasty stuff.