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Technical terminology explained quite simply

Illuminance [lux - lx]

Illuminance (Symbol: E) is the total luminous flux incident on a certain surface per unit area. It is measured in lux (lx). 1 lux illuminance is where an area of 1 square metre is uniformly illuminated by 1 lumen of luminous flux. It can be measured on horizontal and vertical surfaces using a luxmeter. Given the same level of illuminance, a white room appears brighter than a dark one.

sunshine, outside around noon  max. 100.000lx
offices (standard)                                       500lx
clear night with full m                                  0.2lx


Glare can cause an impairment of visual functions (physiological glare) or can reduce visual comfort and lead to eye fatigue (psychological glare). This is due to extreme differences in luminance within an observer's field of view or can be caused by an absolute luminance within an observer's field of view that is too high, so that the observer cannot adapt to it.

Colour temperatures [Kelvin - K]

The colour temperature is measured in Kelvin and describes the luminous colour of a light source. The higher the value, the more cold the object appears under the light. Cold white (daylight white) = 6000 – 6500 KNeutral white = 4000 – 4500 KWarm white = 2700 – 3500K

Colour rendering [Ra]

Natural daylight makes objects and their surfaces appear in their real colours. This lighting situation is the benchmark for artificial lighting in terms of colour perception and thus also defines its quality. The so-called “general colour rendering index (RA)” defines the colour rendering properties of artificial light sources. It measures the ability of light sources to reproduce the colours of objects faithfully, compared with natural light sources. The higher the value, the better the quality of the respective light source. The application defines the colour rendering requirements of light sources.


LED is short for ”Light Emitting Diode”. LEDs are electronic semiconductor components, which emit red, green, yellow and blue light when a current is passed through. Blue LEDs can also generate white light by means of an additional internal fluorescent layer. LEDs are mainly used for orientation lights and sometimes for general lighting purposes. This is mainly due to the specific advantages of different LED technologies, such as long service life, no maintenance, IR/UV-free lighting, low energy consumption, colour stability and shock resistance.

Light output [ɲ]

The light output describes the economic efficiency of a light source. It indicates how many lumens (lm) a lamp produces per Watt (W) consumed. The higher the lumen-watt-ratio, the more efficiently the lamp converts the consumed power into light.

Light spot

This term is mainly used in the field of outdoor lighting, especially street lighting. It refers to the individual lights.

Light spot distance

Used in the field of street lighting to describe the distance between the individual light spots (=lights).

Luminous flux [lumen - lm]

The luminous flux Φ defines the light power of a lamp. It measures the radiant power of light emitted from a light source irrespective of the direction in which it is emitted. The luminous flux is measured in lumens.