Common terms referred to in/or surrounding the standards

Ambient background or surroundings - This is to do with the light around a reflective object for example a sign. How bright the reflective object is seen by the observer is dependent upon this.

Brightness - Brightness is measured just like a vehicle; the more BHP (Brake Horse Power) a vehicle has the more power it has. Brightness is measured in candelas/lux/m2. The more candelas the brighter you are. As the vehicle travels towards you, seeing you earlier allows the vehicle to take evasive action sooner. Therefore the safer you are! The prismatic technology is typically twice as bright as glass bead and because the reflectivity is brighter you can be seen further away with high visibility garments which have prismatic tape on.

Candela (cd) - Often taken as an approximation of the luminous intensity of one candle flame and is equivalent to exactly one unit of luminous intensity. Candlepower (cpl) - Expression of luminosity intensity in candelas - it is the total candela or light output.

Conspicuity - The term refers to something being readily visible or obvious. It is relevant to the standards because the higher the performing tapes or materials used on garments, traffic control devices and vehicles, means that drivers of vehicles have a better chance to see someone or something the more 'conspicuous' they are, enabling a quicker, safer response time.

Entrance angle - The angle made when a light beam strikes at a point on the surface and a line perpendicular to the surface at the same point. It is often used when discussing for example the angularity of reflective materials when applied to backgrounds.

Fluorescence - The giving off of light by a substance when it is exposed to electromagnetic radiation, such as visible light. As long as the light or electromagnetic radiation continues to bombard the substance, electrons in the fluorescent material become excited but return very quickly to lower energy, giving off light, always of the same frequency. This increases the conspicuity of a product increasing the visibility in daytime as well as night-time.

Luminance - The amount of light that we see from a retroreflective surface - measured in units of candelas per metre squared. Luminance refers to what the driver actually sees.

Luminance contrast - Directly the way the background of an object and its luminance interact.

Luminance ratio - The ratio between the luminance (photometric brightness) of any two areas in the visual field.

Microprismatic Technology - Invented by Reflexite over 30 years ago, this is today proven to be the most optically efficient way of providing light to the observer such as a car driver behind the steering wheel at night. Prism technology works by refracting light from its inner surfaces. Light strikes each of the three surfaces of the microprism in turn, before returning to its source. The retroreflective efficiency is enhanced by the precise arrangement of the microprisms, as seen in a microscopic view. The microprism's economical use of surface area delivers the highest standard of reflection. This returns light by as much as 80%. At its longest angle in EN471, Reflexite's material is typically 1000 candelas /lux/m2 - twice as bright as alternative glass bead materials (typically 500 cd/lux/m2.)

Observation angle - The angle between the line formed by a light beam striking a surface and the line formed by the retroreflected beam at an observer's eye. For example, this angle will be larger for the driver of a bus or truck than it will be for the driver of a standard passenger vehicle. Observation angle will also be larger for a driver and vehicle who are very close to a retroreflective sign or device. Large observation angles cause reflective surfaces to appear less bright to the observer.

Photometer - An instrument for measuring light.

Retroreflection - occurs when surfaces return a large portion of an incoming light beam to its source. This is why retroreflective materials appear brightest to observers located near the level of the light source - for example, a driver and the vehicle headlights. Retroreflective surfaces are excellent for use on devices to improve their night-time visibility to drivers.

Retroreflective material - a material that has a thin continuous layer of small retroreflective elements on or very near its exposed surface (for example, retroreflective sheeting, beaded paint, highway sign surfaces or pavement striping).

Retroreflector - a reflecting surface or device from which, when directionally irradiated, the reflected rays are preferentially returned in directions close to the opposite of the direction of the incident rays, this property being maintained over wide variations of the direction of the incident rays.

Source - the object which produces the light.

Stopping sight distance - vitally important. This is to do with the amount of distance required for a driver to stop safely before reaching a person or object in its sight. There is a minimum stopping distance which is the sum of two distances, these being a) the distance travelled from the instant the driver sees an object to the instant the brakes are applied, or the perception-reaction time; and b) the distance required to stop the vehicle after brake application begins (braking distance). 2.5 seconds for perception reaction times is the current guideline - this whole arena is extremely complex when you factor in adverse weather condition and aging drivers etc.

Visibility - The term refers to being able to be seen. In the arena of the standards this is to do with the distance at which an object can actually be seen.

Viewing angle - then angle between the retroreflector axis and the observation axis.