Properties of light sources

This section contains a brief summary of the most common light sources. The data has been complied from the light source manufacturers catalogues and, consequentially, may vary and be subject to change.

Luminous efficacy

A light source’s luminous efficacy is the relation between its luminous flux and the electrical power used. The luminous efficacy is established for the light source or for the system (light source and ballast). The unit for luminous efficacy is lm/W.

Note that the documented value for the luminous efficacy in the tables on the following pages applies to the light source and does not take ballast losses into consideration.

Average mortality rate

The number of burning hours after which half of a large number of controlled light sources have extinguished. Used for incandescent and halogen lamps. 80 % service mortality rate The time after which 80 % of the lighting installation’s original luminous flux remains.

The depreciation in luminous flux depends on the reduction in light output as well as spent light sources.

General colour rendering index, Ra

Colour rendering is a measurement of the light source’s ability to correctly render eight test colours in relation to a fixed reference light. The Ra-index for indoor lighting ought to be above 80 and for good colour rendering above 90. The value for maximum colour rendering is defined as 100.

Colour temperature, K

The colour temperature denotes the light source’s colour appearance and varies in the range 2000–7400 K. 3500–4000 K is considered to be neutral white. Colour temperature lower than 3500 K is experienced as warm and colour temperatures higher than 4000 K are experienced as cold.

Equivalent colour temperatures are stated for fluorescent lamps and discharge lamps.

Colour designation

Light source manufacturers state the light source’s colour properties using a international colour designation consisting of three digits. The first digit represents the light source’s colour rendering and the last two digits stem from the colour temperature in Kelvin, formed by the colour temperature being divided by 100.

A light source with the colour designation 830 has a general colour reproduction index of between 80–89 and a colour temperature of 3000 K.


Light source                                                   

827 830 835 840 850   860  865  927  930  940  950 955  965 
 Fluorescent lamp T5 HE               •   
 Fluorescent lamp T5 HO           •      • 
 Fluorescent lamp T5 Eco                      
 Fluorescent lamp T8 •  •  •  •  •  •  •  • 
 Circular fluorescent lamp T5C                  
 Compact fluorescent lamp FSD-I/E                  
 Compact fluorescent lamp FSD(H)     •     
 Compact fluorescent lamp FSQ-I/E                     
 Compact fluorescent lamp FSM-I/E                  
 Compact fluorescent lamp FSS-I/E