Photoluminescent or phosphorescent pigments are smart materials capable of emitting light after absorbing certain types of radiant energy. More precisely, they absorb invisible ultraviolet (UV) radiation from ambient light and re-emit that energy as visible light in the following hours. Unlike other materials, they don’t reflect light, but they are an actual light source. The duration of the glow effect depends on the amount of radiant energy absorbed. The material appears quite bright at first, but then this effect gradually diminishes over an extended period of time.
Photoluminescent materials are available as ready paint, powder, films and paper. They are provided in different colours, but the brightest one is definitely green. They can be quite durable: for example, Glowtec UK estimates their paints and powders “should enjoy an active lifespan of around 20 years, with a minimum active life of 10 years”.
I find photoluminescent materials extremely fascinating, as they can offer a zero-energy lighting alternative to common light sources and can be applied on most surfaces. Although this sounds very appealing, there are a few significant limitations. First of all, it would be erroneous to think that lamps could simply be replaced by photoluminescent surfaces. In fact, these can be seen only in the dark, even during their brightest phase, so that if there are any competing light sources nearby, you won’t see them glow at all. Moreover, you can’t control them by turning them on and off whenever you like. If you leave them outdoor for 24 hours, you will also notice that after sunset their light is barely perceptible: this happens because they start re-emitting some radiation immediately, while they are still absorbing energy, and the emission gradually becomes less and less bright over time. This means that by the time the dark has come, the material might have emitted most of its light already. Despite those disadvantages that currently make photoluminescent materials impractical in many situations, I think they could already be ideal for applications in interior environments and in remote lands where there are no lights at night. In those cases photoluminescent surfaces could provide enough light for people to recognise places and orient themselves in the dark, which would make them feel reassured and would allow energy saving at the same time.
Detail of photoluminescent Dancing Screen by Eleonora Nicoletti