There are basically two types of variable message sign (VMS) display technology: (1) light-emitting, including light bulbs, light-emitting diodes (LEDs), and optical fibres; and (2) reflective, mainly electromagnetic disk. Light-emitting displays perform best in low-light conditions, at night or on cloudy days. Reflective displays are best in bright daylight. A third type of VMS technology, the hybrid display, combines a reflective flap or disk with a light emitter. It provides the best overall visibility during a 24-hour day, but has hitherto had two problems. The reflective disk can stick, due to the complexity of its mechanical design, and fading can occur due to its reflective coating breaking down under exposure to ultraviolet light. Solutions to these problems include improved designs of electromagnetic shutter, and 3M's Scotchlite Diamond Grade Durable Fluorescent Sheeting material, which enables daylight fluorescent retroreflective hybrid displays. Combining a LED matrix into the new hybrid pixel technology overcomes the severe limitations of VMSs that use only LEDs, because the LEDs need no longer be used under the bright daylight conditions that damage them most. Retroreflective LED hybrid VMSs consume less energy, and can also display messages even in the event of a total power failure.
Abstract