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UGR IN EXENIA PRODUCTS
The UGR index - Unified Glare Rating - defines the level of irritating glare, produced by the light illuminating a room. The index is defined by
many factors which depend on the kind of the fixtures (the emitting surface of the device in relation to the flux play an important role) and the
installation environment since the finishes of the walls, the floor, the location of the furnishings, the presence of windows play a role as well.
"Lb" and " L2" are respectively the luminance of the background and the luminance of the luminous parts of each fixture, "ω" is the solid angle
subtended by the same, "ρ" is the Guth position index (function of the longitudinal distance between the human eye, the transverse plane of
the source and the transverse distance between the eye and the longitudinal plane of the source).
Although today the assessment of the irritating glare level can be processed by means of a lighting design software, the above-mentioned
equation can immediately point out that when defining the UGR parameter, we can consider the background luminance, the overall luminance
of the installed fixtures that are in the same field of view by taking into account the solid angle of view of the observer and the position of
the devices in relation to the observer.
Making it easier, the luminance is a ratio that considers the light reaching our eyes by reflection from an illuminated surface and the light that
comes from an emitting surface. The luminance depends on the intensity of the source and from the apparent area of the surface directed to
the observer. It is clear that the luminance value always depends on the observer position with respect to the lighting source.
The regulations which define the UGR value are in the indoor lighting UNI EN 12464-1 2011, CIE publication 117 standards.
The UGR scale can be considered for minimum values that start at 10 (no glare), up to 30 (high glare). The UGR limits are given every three
units (10, 13, 16, 19, 22 etc.) since every three units there is a change to a diferent class in accordance with the standard,
Some fixtures of our range of products have reference values of the indexes according to the UGR tabular method for reflection coefcients
752 (0.7 ceiling, 0.5 walls, 0.2 floor) which consider X = 4H, Y = 2H as room dimensions (H is the height diference between the eye and the
light sources).
We would like to remind that these values are samples and valid only in case of use of fixtures which are:
• installed in rectangular rooms;
• installed together with other fixtures of the same type and the same level;
• symmetrical and arranged in parallel to the wall.
For further information or evaluations, we recommend making a simulation by means of a lighting design software.
The value is the result of the following equation:
H
y
x
