Luminaire selection

Determining the right lighting technology for luminaires

The choice of LED luminaire also determines the colour of light, the luminous flux and the connected load of the luminaire. In contrast to the built-in LED module, the light distribution of many luminaires is achieved simply by replacing the tertiary lens. Many spotlights also offer the option of brightness control via a potentiometer on the luminaire.

The main criteria for the choice of luminaire are explained below.

Light distribution

Uniform general lighting using wide-beamed illumination

Differentiated lighting using narrow- beam light from spotlights

general - differentiated

Uniform general lighting is a standard lighting concept. For general lighting, wide-beam luminaires such as downlights and light structures are suitable. Uniform lighting can also be achieved by indirect illumination. However, a lighting concept that aims solely to create isolated lighting accents is the exception. Often, accent lighting will contain general lighting components to allow the viewer to perceive the spatial arrangement of the illuminated objects. Spill light from the accentuated areas is frequently sufficient to provide adequate ambient lighting. Luminaires that emit a directed, narrow beam can be used for accent lighting. Adjustable spotlights and directional luminaires are ideal.

Light distribution

Direct lighting with oriented light

Indirect lighting creates an open spatial impression

direct - indirect

Direct lighting allows diffuse and oriented light, and both general lighting and accent lighting. A lighting plan can be used with direct lighting that allows differentiated distribution of light. This greatly enhances the three-dimensionality of illuminated objects as the result of high contrasts.
With indirect lighting, lighting is designed to give diffuse general lighting. Indirect lighting produces a highly uniform, soft light and creates an open appearance due to the bright room surfaces. Problems caused by direct and reflected glare are avoided. Indirect lighting alone can give a flat and monotonous environment.

Light distribution

Wide light distribution for indirect lighting

Narrow-beam light for highlighting

wide - narrow

The decision for narrow or wide light distribution is closely connected with the concept of general or differentiated lighting. Luminaires with a beam angle of less than 20° are known as spotlights and above 20° as floodlights. With downlights, the cut-off angle also gives an indication of the width of the light distribution. Wide light distribution creates a higher proportion of vertical illuminance.

Light distribution

Downlights with symmetrical light distribution for general lighting

Asymmetrical light distribution of wallwashers for uniform wall illumination

symmetrical - asymmetrical

Symmetrical light distribution is used for providing even lighting. The light distribution can be wide for downlights used for the general lighting of horizontal surfaces. With spotlights, the light distribution is narrow beamed to provide highlighting. Luminaires with asymmetric light distribution are designed to give uniform light distribution for surfaces located to one side. Typical luminaires with this characteristic are wallwashers and ceiling washlights.
For luminaires with axially symmetrical beam emission, such as light structures, two light intensity distribution curves are given.

Light distribution

Horizontal lighting for workplaces

Vertical lighting accentuates the texture using facade lighting

horizontal - vertical

Focusing on horizontal lighting is frequently in line with the decision to plan functional, user-orientated light. This applies to the case of lighting for workplaces for instance, where the lighting design is primarily aimed at giving uniform lighting for horizontal visual tasks. In such cases, vertical lighting components are predominantly produced by the diffuse light that is reflected by the illuminated, horizontal surfaces.
The decision to plan vertical lighting may also be related to the task of fulfilling functional requirements when illuminating vertical visual tasks, e.g. for shelves, blackboards or paintings. However, vertical lighting frequently aims to create a visual environment. Vertical lighting is intended to emphasise the characteristic features and dominant elements in the visual environment. This applies not only to the architecture itself, whose structures can be clearly portrayed by illuminating the walls, but also to the accentuation and modelling of the objects in the space.

Light distribution

Custom design

In most cases the choice of luminaires will be confined to the standard products available, because they can be supplied at reasonably short notice, have clearly defined performance characteristics and have been tested for safety. Standard luminaires can also be used in special constructions, such as lighting installations that are integrated into the architecture (e.g. cove lighting or luminous ceilings). In the case of large-scale, prestigious projects consideration may also be given to developing a custom designed solution or even a new luminaire. This allows the aesthetic arrangement of luminaires in architecture or in a characteristically designed interior and the solution of specific lighting tasks to be effected in closer relation to the project than if only standard products are chosen. Additional costs for development and time considerations must be included in the calculation of overall costs for the project.

Luminous colour

The colour of light from a luminaire depends on the lamp. The range of white light colours is divided into warm white (3000K) and neutral white (4000K).
Other white or saturated light colours can be produced with luminaires having RGB or varychrome RGBW technology.
With luminaires having RGB technology, red, blue and green primary colour light sources can be mixed to give a multitude of colours.
Varychrome RGBW luminaires have warm white LEDs in addition to red, green and blue LEDs resulting in a significantly better colour rendition quality.
Coloured LED luminaires are usually controlled using a DALI system. This allows the light colour to be changed dynamically as well as setting a permanent saturated colour or a very warm or cold white.

Methods of mounting

Methods of mounting

There are two basic contrasting concepts for the arrangement of luminaires in an architectural space, which can allocate different aesthetic functions to the lighting installation and provide a range of lighting possibilities. On the one hand, there is the attempt to integrate the luminaires into the architecture as far as possible, and on the other hand, the idea of adding the luminaires to the existing architecture as an element in their own right. These two concepts should not be regarded as two completely separate ideas, however. They are the two extremes at either end of a scale of design and technical possibilities, which also allows mixed concepts and solutions. The decision to opt for a stationary or variable lighting installation overlaps the decision to go for an integral or additive solution; it is determined by the lighting requirements the installation has to meet rather than by design criteria.

Methods of mounting

Integral lighting

In the case of integral lighting, the luminaires are concealed within the architecture. The luminaires are only visible through the pattern of their apertures. Planning focuses on the lighting effects produced by the luminaires. Integral lighting can therefore be easily applied in a variety of environments and makes it possible to co-ordinate luminaires entirely with the design of the space. Integral lighting generally presents a comparatively static solution. The lighting can only be changed by using a lighting control system or by applying adjustable luminaires. Typical luminaires here are recessed wall or ceiling luminaires.

Methods of mounting

Additive lighting

In the case of additive lighting, the luminaires appear as elements in their own right. Besides planning the lighting effects which are to be produced by these luminaires, the lighting designer also has to specify the luminaire design and plan a lighting layout in tune with the architectural design. The range extends from harmonising luminaires with available structural systems to selecting luminaires that will have an active influence on the overall visual appearance. What is gained in flexibility is offset by the task of harmonising the visual appearance of the lighting installation with its surroundings and of avoiding the visual unrest through the mixing of different luminaire types or by a confusing arrangement of light structures. Typical luminaires here are spotlights and light structures, as well as pendant luminaires.

Methods of mounting

Stationary lighting

With stationary, mounted luminaires, different light distributions are available, e.g. adjustable luminaires such as directional luminaires. The luminaire layout should be thoroughly checked in the design phase because any subsequent alterations to recessed luminaires are very costly.

Methods of mounting

Movable lighting

There are different ways of making a lighting installation flexible. The highest degree of flexibility, as required for lighting temporary exhibitions and for display lighting, is provided by movable spotlights mounted on track systems or support structures. These allow the luminaires to be realigned, or even rearranged or replaced.



In the case of adjustable luminaires, such as spotlights or directional luminaires, glare also depends on the light distribution of the luminaire. Glare primarily occurs if the luminaire is not correctly adjusted.
In the case of stationary luminaires, such as downlights or light structures it is necessary to distinguish between the elimination of direct glare and reflected glare. In the case of direct glare, the quality of glare limitation depends on the light distribution of the luminaire. The greater the cut-off angle in downlights, the greater the visual comfort provided by the luminaire due to improved glare control.


By projecting the field of vision onto the ceiling surface it is possible to define the area in which the luminaires may have a negative influence on contrast rendering.


Standards exist for the lighting of workplaces, which stipulate minimum cut-off angles or highest permissible luminances in the cut-off range. For workstations with VDTs there are specific requirements. The critical area can be defined as that portion of the ceiling which is seen by the user in a mirror covering the working area. In the case of luminaires with mirror reflectors direct glare control improves the greater the cut-off angle. The standard cut-off angles are 30° and 40°.
The UGR (Unified Glare Rating) process is used to evaluate and limit the direct discomfort glare in indoor areas. The UGR value is influenced by the light source's luminance, its visible size (solid angle) and its position (position index), as well as the luminance of the background. It is usually between 10 and 30. The smaller the UGR value, the less the glare.


Recommended illuminance level E according to CIE for various activities

Visual performance generally improves sharply as the illuminance level is increased. Above 1000 lux, however, it increases more slowly, and at extremely high illuminance levels it even starts to decrease due to glare effects. However, following a set of fixed rules for illuminance levels gives little consideration to actual perception. It is not the luminous flux falling on a given surface - illuminance - that produces an image in the eye, but the light that is emitted, transmitted or reflected by the surfaces. The image on the retina is created entirely by the luminance pattern of the perceived objects, in the combination of light and object..

Safety requirements

Identification of protection mode (IP):
code Y, water protection

Protection mode

Luminaires are required to meet the safety requirements in all cases; in Germany this is usually guaranteed by the presence of a test symbol. In some cases there are other requirements that have to be met and the luminaires marked accordingly. Special requirements have to be fulfilled by luminaires that are to be operated in damp or dusty atmospheres, or in rooms where there is a danger of explosion. Luminaires are classified according to their mode of protection and protection class, whereby the protection class indicates the type of protection provided against electric shock, and the mode of protection its degree of protection against contact, dust and moisture.

Safety requirements

Identification of special luminaire properties and safety requirements

Protection classes

Special requirements to fire safety have to be fulfilled when luminaires are installed in or on furniture or other inflammable materials.

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