Technical definitions

In the following we wish to explain several important technical definitions for a better understanding


  • The specification of the lighting intensity with which a light source radiated in a particular direction (room angle, reflector lamps).

  • Photometric property, in order to measure how bright or dark the light of a lamp acts on human perception.
  • 1 cd corresponds approximately to one normal household candle.

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Lighting agent

Light intensity in Candela



40W bulb


100W bulb


40W fluorescent bulb





Specification of the light colour as a colour temperature. This refers to the temperature to which a dark body would theoretically have to be heated, in order to emit light of the same colour.

The temperature definition by Kelvin starts from absolute zero (-273.15 °C). The temperature difference of 1K corresponds to a temperature difference of 1 °C.

Celsius / °C

Kelvin / K

Fahrenheit / °F
















Light source

Colour temperature

Red heat

500 K


1500 K

40W bulb

2680 K

100W bulb

2800 K

200W bulb

3000 K

Halogen bulb

3200 K

Late evening sun before twilight

3500 K

Cold white fluorescent tube

4000 K

Morning/evening sun

5000 K

Early morning/late afternoon sun

5500 K

Midday sun

5500 - 5800 K


6000 K

Overcast sky

6500 K - 7500 K


8000 K

Blue sky in the shade

9000 - 12000 K

North light

15000 - 25000 K


  • Radiation performance of a lamp, which is specified in the range of visible light.

  • A certain quantity of light is emitted in a certain time; the flow of light continues as long as the lamp remains on (physiological property – in contrast to Watts = physical unit).

  • By means of the light flow, it can be determined whether a lamp gives off more or less light than another lamp. Further judgements such as the efficiency of the light generation cannot be made.


The light yield of a light source can be calculated from the light flow and power consumption.

100W bulb = 1400 Lumen = 14 Lumen per Watt (lm/W)


Average light yield of common lamp technologies


14 lm/W

Halogen bulb

24 lm/W

Energy-saving bulb

66 lm/W

LED lamp

100 lm/W


Lux is the unit of lighting intensity. This is used in various regulations, such as workplace guidelines as the specification for the lighting of workplaces.

Lighting intensity

Lighting intensity Lux

Bright sunny day


Overcast summer day


Summer in the shade


Operating theatre


Overcast winter day


TV-Studio lighting


Office/room lighting


Hall lighting


Street lighting


Candle at approx. 1m distance   



Common sockets:

230V - high voltage

12V - low voltage

Holders for plug-in energy saving lights:

Protection classes

Definition: Protective measure in the event of failure of the basic or operating insulation protection on indirect contact in accordance with DIN VDE 0100 T200 

Protection class 1: Protective earthing, protective conductor on equipment housing.
Protection against electric shock is not based solely on the basic insulation: conductive parts which can be contacted, and which can become live in the event of a fault, are also connected to the mains protective conductor. The protective conductor terminal is designated by a symbol.

Protection class 1
Protection class 1

Protection class 2: Protective insulation
Live parts are provided with additional protective insulation against contactable metal parts. The connection of the protective conductor is not allowed.

Protection class 2
Protection class 2

Protection class 3: Protective low voltage, <50V, for lights and transformers for lights.
The protection against electric shock is based on the use of protective low voltage (safe extra low voltage - SELV).

Protection class 3
Protection class 3

Protection types

The designation of the protection type consists of the letters IP, followed by two numbers (in accordance with DIN VDE 0470)

The most important/frequent protection classes are:

  • IP20
  • IP60
  • IP65
  • IP67
  • IP44

The first number specifies:

Protection against foreign bodies (protection against the ingress of solid foreign bodies including dust) 

0 unprotected

1 protected against solid foreign bodies > 50 mm (back of the hand)

2  protected against solid foreign bodies > 12 mm (finger)

3  protected against solid foreign bodies > 2.5 mm (tool)

4  protected against solid foreign bodies > 1 mm (wire)

5   protected against dust

6   dust-proof

The second number specifies:

Protection against water (protection against the ingress of water with harmful effects)

0 unprotected

1 protected against dripping water (vertical)

2 protected against dripping water (below 15°)

3 protected against dripping water (below 60°)

4 protected against spray water

5 protected against hose water

6 protected against strong hose water

7 protected against the consequences of immersion (30 min. to 1 m depth)

8 protected against submersion (longer/deeper than “7”, following agreement between the manufacturer and user)