Some issues I noticed from my first short test were that is is difficult to gauge what will be in the picture and what not. For the prototype that I want to make to place in a school, it would be good to design some restraints and allowances to guide the participants.
Another is that for good light art, the surroundings should be somewhat dark, at least darker than the light source used. This makes the school yard an unlikely location during daylight hours. That is a shame, because that is where a lot of teenagers spend their breaks.
One good location would be the sports hall, as it would be easy to black out, and it offers a lot of space to move around. Also, there already are constraints to where you could paint light, in the form of walls and ceilings. Another option could be the lunch area inside. What I don’t like about the sports hall, is that this would make the light painting more of an organised activity, instead of one that bored teenagers could easily engage in during lunch break.