The assessment of unpleasant glare in rooms and workplaces involves comparing the Unified Glare Rating (UGR) determined in the lighting design with the limit value (maximum acceptable glare) of this parameter, in accordance with EN 12464-1. It is therefore assumed that unpleasant glare is limited if the UGR requirements are met in the lighting design. However, even such an assessment is not performed, as the employer usually does not have documentation of the lighting design. Thus, glare is not a parameter to be monitored and assessed objectively in the working environment, mainly due to the lack of a standardised measurement method and measuring device. However, such an assessment should be carried out to check compliance with the provisions of 26.2, 39.1 and 40.1 of the Decree of the Ministry of Labour and Social Policy on general health and safety regulations.
Lb - background luminance, L - luminance of the luminous parts of each luminaire towards the eye of the observer, w - solid angle of the luminous parts of each luminaire towards the eye of the observer, p - Guth's position index for each individual luminaire, which refers to the position of the luminaire relative to the line of sight.
The index takes values from 10 to 30.
UGR and perceived discomfort
10 not noticeable13 barely noticeable16 noticeable19 acceptable22 unacceptable25 barely tolerable28 unbearable
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The UGR (Unified Glare Rating) is a standardised glare rating index that determines the degree of visual discomfort caused by light sources in a room. It is an international standard used to assess unpleasant glare in interior lighting.
Acceptable UGR values depend on the type of room and the work being performed. According to EN 12464-1:- Offices, meeting rooms: UGR ≤ 19- Industrial rooms: UGR ≤ 22- Corridors, circulation areas: UGR ≤ 25- Precision work rooms: UGR ≤ 16
Too much glare can cause visual fatigue, reduced concentration and productivity, and consequently increase the risk of accidents. Long-term exposure to glare can lead to permanent visual problems and headaches.
The UGR rate can be reduced by:- Using luminaires with shades or louvers- Using luminaires with low UGR (labelled ‘low UGR’)- Appropriate positioning of luminaires in relation to workstations- Use of matt surfaces in rooms- Increase in background luminance (e.g. brighter walls)
Yes, in Poland, according to the MPiPS regulation on general health and safety regulations (regulations 26.2, 39.1 and 40.1), the employer is obliged to ensure appropriate lighting conditions, including the reduction of unpleasant glare.
UGR measurements should be carried out upon acceptance of a new lighting installation and after any significant modification of the lighting system or change of room layout. Periodic inspection (e.g. every 2-3 years) is also recommended as part of maintaining appropriate working conditions.
Too high a UGR can lead to:- A decrease in employee productivity of 15-20%- Increased risk of accidents at work- Health problems (headaches, eye fatigue)- Non-compliance with health and safety regulations- Legal liability of the employer
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