In lighting design, UGR < 19 has been widely used as the upper limit of glare control. However, the UGR value output by most current design software is not the "applied UGR" (UGRAppl) recognized by the CIE standard.
1. UGR＜19≠Not Glaring
UGR (Uniform Glare Rating) is one of the key indicators used to evaluate discomfort glare in indoor lighting design. In most projects, "UGR<19" has become synonymous with comfortable lighting.
However, the UGR value output by default in most software currently does not conform to the UGRAppl defined by the CIE standard, but UGRPoint; and the UGRLum marked in many lamp manuals cannot represent the actual glare level of the space.
2. Origin and basic principle of UGR
UGR was first proposed by the International Commission on Illumination (CIE) in CIE 117:1995 and expanded in the subsequent CIE 190:2010. It is an empirical formula for quantitatively evaluating the glare caused by indoor artificial lighting.
Its basic calculation formula is as follows:
- Ls: brightness of the light source in the viewing direction;
- ω: solid angle of the lamp at the viewpoint;
- p: position index (Guth Index), reflecting the relationship between the lamp and the line of sight angle;
- Lb: background brightness, excluding direct light from the lamp.
3.Three types of UGR and their differences
|
Type |
UGRAppl |
UGRLum |
UGRPoint |
|
Source |
CIE 190:2010， |
Lighting Manufacturer Data |
Software default output |
|
Definition |
Application-based UGR: |
Luminaire UGR: |
Point-source UGR: |
|
Feature |
It considers key factors such as spatial reflectivity, lighting layout and viewing direction |
It is convenient for quick comparison of the glare control capabilities of the lamp itself |
It only reflects the instantaneous UGR value of a certain observation point in a specific direction |
|
Can it be used to determine UGR<19? |
Can directly determine UGR < 19 |
Can be used for reference, but cannot be used for actual space judgment |
Both CIE and NEMA point out that UGR Point cannot represent the visual comfort of the entire space, nor can it be used to determine whether UGR <19. |
|
Application scenarios |
Overall glare assessment of actual installation environments (such as offices and classrooms) in accordance with CIE standards (EN 12464-1/GB 50034). |
During the factory testing or selection stage of lamps, the inherent glare characteristics of a single lamp (such as the UGR value marked in the product catalog) are evaluated. |
The glare contribution analysis of discrete point light sources (such as spotlights and downlights) is suitable for local accent lighting design. |
4. How do lamp structure and light distribution form affect UGR perception?
Shielding angle and visible light source control
Shielding angle refers to the angle between the horizontal direction of the observation point and the shielding edge of the lamp. It is not directly involved in the UGR calculation, but it is a key structural parameter that affects the perception of glare.
The larger the shielding angle, the more difficult it is for the light source to enter the field of vision, and the weaker the glare;
When the shielding angle is < 20°, the human eye is very likely to look directly at the light source, and the glare risk is high;
It is usually recommended that the shielding angle ≥ 30° is the design lower limit for office, teaching, medical and other spaces.
Engineering advice: It is preferred to use lamps with deep cup reflectors, honeycomb grilles, black mirror covers or shading frames to improve shielding and optimize the visual experience.
Asahi’s 1X2 1X3 1X4 1X5 1X7 LIENAR LENS with different type cover is designed with the optical grill for better UGR and anti-glare control.
The original intention of the UGR index is to help designers control uncomfortable glare in the room, and its meaning should not be simply equated with "UGR < 19 = not glaring". Only by placing UGR in the overall relationship between space function, human eye behavior, lamp design and light environment can its evaluation function be fully utilized.