What if architectural and urban surfaces could emit light with no need of electric power? The luminescent façade frame of the Media-TIC building in Barcelona already suggests the possibility of illuminating cities with smart coatings that act as a zero-energy, outdoor lighting solution. In London it was recently planned that Hammersmith and Fulham Council will use a spray-on, light-emitting coating by Pro-Teq Surfacing to light up the main route through William Parnell Park in Fulham: the Starpath will absorb daylight and will release it at night, creating a blue glow that will improve the safety in an environmentally-friendly and cost-effective way. Studio Roosegaarde even proposed to light up roads with glow-in-the-dark lines.
Photoluminescent coatings are also referred to as glow-in-the-dark, phosphorescent, luminescent, illuminous or luminous paints. If more urban surfaces were coated with such paints, daylight could be stored and “reused” at night, which would allow cities to save energy and to reduce CO2 emissions. In fact, 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. In the dark the material appears quite bright at first, but then this effect gradually diminishes over an extended period of time.
Photoluminescent materials are available as paint, powder, films and paper. They are provided in different colours, but the brightest one is green. They can be quite durable: for example, Glowtec estimates their paints and powders “should enjoy an active lifespan of around 20 years, with a minimum active life of 10 years”, besides being designed to be highly versatile and suitable for most interior and exterior uses. In fact, those paints are water and weather-proof and can be applied on a variety of substrates such as wood, metal, plastic, paper, fabric and masonry, although it is recommended to use a white, or a light colour as the background for the brightest results.
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 limitations. First of all, the photoluminescence can be noticed only if there are no competing bright light sources nearby. Moreover, you can’t control photoluminescent surfaces by turning them on and off whenever you like. Despite those characteristics, I think photoluminescent pigments could be ideal for applications in environments that are dark at night, to replace electrically powered lights. For examples, they could be used to create glowing pavements, walls, architectural screens and blinds, shop windows, urban furniture and much more. 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.