Types of reflection
Generally, reflection is like follows.
Specular Reflection
Specular reflection is the reflection of light from a smooth surface that is reflected to the opposite angle of the original light source. Reflected light is reflected directely to the original light source only if refllected at a 90C angle to the light source.
Diffuse Reflection
Diffuse reflection is the that of light from a rough surface. Even though light is reflected, the object which has the rough surface cannot be recognized well. Retro Reflection
Retroreflection occurs when surfaces return the directed light to its source. This is why retro-reflective materials appear brightest to observers located near the light source. For example, a person who drives a car using vehicle headlights can view any angle, which makes retro-reflective surfaces excellent for night visibility.
Retro-reflective materials come in all the legally required sign colours. They return the light such that it is seen in the same colour as that of the sign. Thus all original sign colours, shapes and sizes can be clearly seen by means of the retro-reflected light at all times.
Driving conditions are such that most often dipped (passing) beams are used to avoid glare for oncoming traffic, since high beams can only be lit when there is no opposite traffic. In fact, the UN Conventions prescribes the dipped beam as the minimum requirement when a vehicle is in movement at night - even on lit streets - and in bad weather conditions.
The further away from the sign one, is the more retro-reflected light reaches the eyes of the driver. As one gets closer to the sign more light gets directed back to the head-lamp(s) and less to the driver's eyes (principle of the Cone of Retro-reflection). The angle formed between the headlamps, the sign and the observer's eyes gets larger. In other words, the perceived brightness of the retro-reflected light diminishes as the vehicle gets closer to the sign. This explains the fact why it is practically impossible to obtain uncomfortable glare from retro-reflective signs.
This is also confirmed by the fact that more than ninety percent of all road signs are situated at the edge of the road, roughly two metres above the ground. Overhead signs are normally placed some four and a half to five metres above the carriageway.
New technical developments
Vehicle Head Lamps:
New technologies in headlamp design allow for better light emission control. The inventions of new light sources combined with novel light beam patterns provide improved distribution of road and sign illumination. A global dipped (passing) beam has been technically and legally described in 2002 (UN ECE Documents currently under consideration for approval at the World Forum for Harmonised Vehicle Regulations - WP.29). Certain models of motor vehicles are already fitted with such beams. This will lead to common geometrical visibility criteria for road signs.
Retro-reflective materials:
The computerised technology leading to the design and manufacturing of retro-reflective sign sheeting has resulted in a considerable improvement in day and night road sign performance. A new generation of high-tech retro-reflective products is now available. These modern materials are based on micro-replication of corner-cubes eliminating the need to use glass beads and their aluminium backing. The new materials are made entirely of plastic materials and provide a far more efficiently distributed and brighter retro-reflected light with richer colours.
Road signs using this high performance sheeting respond well to specific function requirements and provide the best possible performances in relation with their position along or above the carriageway. New families of micro-corner cube retro-reflective materials are designed to allow authorities to consider replacing totally their illuminated signs whilst retaining similar and in some cases even better efficiency. Thereby they are able to enable considerable return of investment as well as create substantial economies over long periods of time.
