The Unified Glare Rating (UGR) quantifies discomfort glare, ensuring proper lighting design for indoor environments. Developed by the International Commission on Illumination (CIE) in 1995, UGR standardizes glare assessment.

UGR — Unified Glare Rating Calculator

Background luminance (Lb) · Units (for guidance) Observer & context

Luminaires (add one row per luminaire seen by observer)

Luminance L (cd/m²)	Solid angle ω (sr)	Position index p	Actions

Formula used: UGR = 8 · log10( (0.25 / Lb) · Σ (Lᵢ² · ωᵢ / pᵢ²) )

L = luminance of the luminaire in cd/m², ω = solid angle, p = Guth position index. Enter at least one luminaire and a positive background luminance.

Scenario	Lb (cd/m²)	Typical UGR range (approx.)
Office, computer work	3–6	10–22
General retail, shop	5–20	12–24
Executive office	1–3	8–16

UGR Calculation Formula and Variables

The UGR is calculated using the following formula:

Detailed Explanation of Variables

Background Luminance (L_b): Represents the average brightness of the room’s background surfaces, such as walls and ceilings. This value influences the eye’s adaptation level and affects glare perception.
Luminance of Each Light Source (L_n): The brightness of each luminaire visible to the observer. Higher luminance values increase the likelihood of discomfort glare.
Solid Angle (ωn): The angular size of the light source as perceived by the observer. Larger light sources subtend a greater solid angle, contributing more to glare.
Guth Position Index (p_n): A dimensionless factor that adjusts for the position of each light source relative to the observer’s line of sight. It accounts for the angular displacement of the light source from the observer’s direct view.

Common UGR Values and Their Implications

The following table outlines typical UGR values and their corresponding levels of discomfort glare:

UGR Value	Discomfort Level	Recommended Applications
10	Negligible glare	Auditoriums, cinemas, art galleries
13	Very low glare	Offices, classrooms, libraries
16	Low glare	Conference rooms, meeting areas
19	Moderate glare	Open-plan offices, workstations
22	High glare	Industrial settings, workshops
25	Very high glare	Warehouses, production areas
28	Extremely high glare	Kitchens, bakeries, heavy industry
30	Unacceptable glare	Areas requiring visual precision

Note: Values are based on CIE 117-1995 and EN 12464-1 standards.

Real-World Application Examples

Example 1: Office Lighting Design

Scenario: Designing lighting for an open-plan office with a ceiling height of 2.7 meters, using LED panel luminaires with a luminous flux of 4000 lm.

Calculation Steps:

1.Determine Room Parameters:

Room dimensions: 10m x 8m
Ceiling reflectance: 0.8
Wall reflectance: 0.5
Floor reflectance: 0.3

Select Luminaires:

3.Calculate Background Luminance (L_b):
Using the room’s reflectance values and dimensions, calculate the background luminance.

4.Apply UGR Formula:
Substitute the values into the UGR formula to compute the discomfort glare level.

Outcome: The calculated UGR value is 18, indicating a low level of discomfort glare, suitable for office environments.

Example 2: Industrial Workshop Lighting

Scenario: Designing lighting for a workshop with a ceiling height of 4.5 meters, using high-bay LED luminaires with a luminous flux of 15000 lm.