Definition #
The UGR value is therefore not intrinsic to the luminaire, and is only meaningful in a given configuration.
This system for assessing glare in a room by calculating the UGR value replaces the old Bodmann and Söllner abacus method and the A, 1, 2, 3 quality classes.
For indoor workplaces described in European standard EN12464-1, CIE publication 117-1995 defines the Unified Glare Rating (UGR) method.
This notion of UGR is only relevant in the case of a windowless interior and for direct lighting luminaires with uniform, medium-sized light-emitting surfaces (between 50 cm² and 1.5 m²).
The UGR is calculated using a complex formula whose basic principle is to compare the luminance of luminaires with the luminance of the environment, in order to estimate the contrast perceived by the eye as a function of the observer’s position.
Values #
The UGR is given by a value between 10 and 30.
For indoor workplaces, standard EN12464-1 recommends maximum UGR values for different applications, with deviations of less than 3 being insignificant.
Methods #
There are three approaches to determining the UGR, all based on the above formula.
Direct calculation (for an installation) #
By directly applying the UGR formula using software, we can calculate a UGR value for a given installation, corresponding to an observer’s position.
This method requires you to have previously defined all the details of the lighting project: dimensions and colors of the room, user location, direction of gaze and, of course, the actual layout and type of luminaire chosen.
It’s a precise but cumbersome method, and therefore rarely used in practice.
The manual tabular method (for one installation) #
For a luminaire with symmetrical light distribution, a table of UGR values corresponding to a conventional layout of ceiling-mounted luminaires in a rectangular room of a given size and at various predetermined positions of an observer can be edited.
This table can be used to quickly assess the glare level of an installation once its main characteristics are known.
The quick method (for one luminaire) #
In cases where the project data are not yet known, and for the purpose of quickly comparing luminaires with each other, a UGR value can be determined using the above tabular method, but in a predefined standard configuration.
By convention, consider a room with dimensions 4H/8H, reflection coefficients ρ of 70/50/20 and a luminaire spacing of S=0.25H. The highest value of the four possible configurations (viewing direction in relation to the room and in relation to the luminaires) is then used.
This method is used to assign a UGR to all symmetrical, medium-sized, direct-illuminated luminaires intended for ceiling mounting in interior lighting.
This value makes it quick and easy to compare luminaires with one another. For all our luminaires that allow this, we indicate the maximum UGR value on the product data sheet.
Nota
For certain luminaires where the direction of observation is decisive, we indicate two UGR values:
- UGR 0° corresponding to observation from the side of the luminaire (first column of the table).
- UGR 90° corresponding to an observation along the length of the luminaire (second column of the table).
Luminance L65° Luminance L65° Luminance L65° Luminance L65° Luminance #
Luminance is a quantity used to quantify the “brightness” of a surface in a given direction.
For computer work, EN 12464-1 defines limit values to avoid annoying reflections on vertical display screens. The value L65° is used, corresponding to the average luminance of the luminaire seen at an angle of elevation γ between 65° and 90° and in all radial directions around the luminaire.
For standard screens (i.e. high luminance screens > 200 cd/m²), use a luminaire with :
L65° ≤ 1500 cd/m² in the case of a dark screen or a very demanding visual task.
L65° ≤ 3000 cd/m² for a screen with a white background
Scrolling #
In the case of luminaires fitted with devices to conceal the light source (louvres), EN 12464-1 defines an angle α, corresponding to the maximum angle at which the lamp is not visible.
As our luminaires are linear, we distinguish between :
- Transverse scrolling
- Longitudinal scrolling
