The most important parameter for retroreflective products is the specific retroreflection value R′. It indicates the light intensity of the light source in relation to the illuminance of the film and the illuminated surface. Accordingly, the unit for the reflection value is R′ = cd/(lx-1*m-²).
The luminous intensity refers to the light source and is given in candela (Latin for candle - 1 cd corresponds to the luminosity of 1 candle). It forms the starting value for the luminance.
The luminance is the ratio between the luminous intensity and the size of the illuminated surface. It is mainly used for monitors and displays. For example, a white LCD monitor has an average luminance of 250-300 cd/m².
If the illuminance (also known as luminous flux density) of the illuminated reflective film is also taken into account, the specific reflectance value R′ is obtained. Illuminance is the intensity of the luminous flux that falls on a certain area (e.g. 1 m² of reflective film).
The reflection value also depends on the angle of observation and the angle of incidence. The greater the observation angle, the lower the reflectance. The same applies to the angle of entry: the greater the angle of entry, the lower the reflectivity.
Last but not least, the colour of the reflective film also plays a role in determining the reflective value: as the print colour impedes the light during reflection, films printed in green or blue, for example, offer significantly lower reflective values than yellow or orange ones. Silver/white reflective films offer the brightest reflection.