‘Next Bus Signs’ Glow in the Dark
MOGO produces signs which can be read in the dark, either by printing directly onto a photo-luminescent panel (MOGLO) or by printing the graphic onto clear film which is layered over MOGLO. This panel is then charged by either natural daylight or another source of light and when dark, the illuminated sign can be read clearly without the need for any external power source.
How does it work?
Photoluminescence (abbreviated as PL) is a process in which a substance absorbs photons (electromagnetic radiation) and then re-radiates photons. Quantum mechanically, this can be described as an excitation to a higher energy state and then a return to a lower energy state accompanied by the emission of a photon. This is one of many forms of luminescence (light emission) and is distinguished by photoexcitation (excitation by photons), hence the prefix ‘photo‘. The period between absorption and emission is typically extremely short, in the order of 10 nanoseconds. Under special circumstances, however, this period can be extended into minutes or hours.
For how long is it effective?
Photo-luminescent panels are manufactured to a variety of specifications and the substrate used in MOGO’s ‘Next Bus Signs’ is designed to charge reasonably quickly. Once the panel is fully charged to the moment it ceases to absorb photons, ie. receive light, its brightness starts to fade – slowly. Common experience indicates that these signs can be read in total darkness for up to six hours. It must be understood that all human eyes are variously efficient, but the sixty-four year old eyes of this contributor can still decipher 12 point, black text printed onto MOGLO six hours after lights out!
One of the major uses of photoluminescent material is for safety and egress marking. It is most commonly seen in the form of “fire exit” signage. The industry is governed by a number of international standards and guidelines that stipulate performance criteria under certain conditions of excitement, both luminary and human.Extracts taken from Wikipedia.
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