What is UGR?

Within the realm of luminescence schematics, the UGR (Unified Glare Rating) coalesced dazzle metric operates as an indicator of interior illumination comfort levels. As the significance of workplace and scholastic illumination surges, UGR discussions burgeon. Nevertheless, under which circumstances is UGR computation necessitated, and what is the optimal utilization approach?

UGR values span from 10 to 30, with larger figures correlating to increased discomfort from direct glare within interior spaces. For instance, a UGR of 19 signifies that 65% of occupants experience no glare interference, while the remaining 35% encounter visual discomfort due to light impinging on their line of sight.

A prevalent misconception is that UGR signifies luminaire attributes; however, this notion is erroneous. UGR derives from calculations rather than assessments of glare through light distribution files such as IES. The resulting value considers the luminous surface of the luminaire, user or observer angle and position, and the ambient environment. UGR is unsuitable for lamps emitting 65% or more indirect light or for narrow-angle spotlights and asymmetric luminaires.

To elucidate the interplay between these factors, envision traversing a pitch-black street devoid of streetlights when suddenly, an approaching vehicle illuminates the path. The intense beams cause immediate glare and transient blindness, hindering your ability to discern the road. Conversely, on a starlit summer night, encountering the same vehicle generates significantly less ocular discomfort, despite the headlights remaining unaltered. The background luminosity alters the perceived glare intensity. Furthermore, the observer’s position and line of sight are crucial; if the lamp is outside the observer’s view, glare becomes inconsequential.

Regulations for activity spaces such as offices and libraries mandate UGR consideration in lighting design. Lighting professionals can employ the glare rating scale delineated by the International Commission on Illumination CIE 117-1995. This table streamlines intricate equations to assess whether a design complies with UGR stipulations.

Nonetheless, the scale has limitations. The UGR value calculates the dazzle quotient for a solitary lighting fixture within a standardized space, which may not align with the actual environment. The scale’s formula incorporates the highest reflection coefficients of 20% for floors, 30%-50% for walls, and 50%-70% for ceilings. However, it neglects the 75%-90% reflectance observed with white walls or ceilings in edifices. Another constraint is the observer’s position, which must be parallel or perpendicular to the luminaire, but not diagonal. Moreover, the scale exclusively accounts for rectangular spaces and does not accommodate other geometries. Integrating the UGR of disparate luminaires within a single space poses a conundrum.

Illumination manufacturers often denote “UGR <19” within product descriptions. Ideally, other pertinent parameters should be specified, such as 4H/8H in the space and reflection coefficients of 20% for floors, 50% for walls, and 70% for ceilings.

▲ UGR scale of DIALux

In general, UGR tables surface in DIALux reports, while more comprehensive analyses can be conducted utilizing DIALux UGR calculation points or UGR surfaces.

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