Question: i want to make a graffiti wall for our museum...your idea of writing with light on a fire exit sign has potential...can you tell me what the fire exit is made of or where i could get a large piece
The effect of absorbing light and reemitting it at a later time (with lower energy) is called phosphorescence and I am sure you have already seen lots of ‘glow in the dark’ stuff. The writing will fade over time, it is not permanent and usually lasts at most a couple of hours.
You can buy either paint or sheets just google ‘phosphorescent sheet / paint’.
I love the idea of the graffiti wall as a giant guestbook. There is one in Barbican that works really well. As for the technology I don’t think fluorescence could work as a long standing graffiti wall as the paint will only glow for a limited amount of time. In fact what happen is that the light emitted by the source, in the case of the lecture the phone LED, will be absorbed by the material and then slowly reemitted in the course of a few minutes or hours. If you are interested on how to make this see this tutorial:
In the lecture we used a large sheet of photo luminescent paper which we purchased online. It is certainly fun to play with using torches and smart phone lights.
While it would certainly be fun for people to create light graffiti it is important to remember that the graffiti wouldn’t last very long. It starts to fade instantly and would have disappeared within about 30 seconds – depending on the strength of the light etc.
It is also useful to note that this experiment works best when the surrounding area is dark so that there is less “light pollution” on the sheet.
All that being said it is still lots of fun. The Science Museum in London has a large wall of photo luminescent plastic in their Launchpad Gallery which they use as an interactive to allow children to do experiments with light.