Unified Glare Rating (UGR) in Solar Street Lights

Understanding Unified Glare Rating (UGR) in Solar Street Lights

UGR full form: Unified Glare Rating is one of the crucial parameters for assessing the lighting quality of solar street lights. UGR measures the degree of discomfort glare caused by a light source in the observer’s visual field. This article provides a detailed analysis of UGR in solar street lights, including influencing factors, standard requirements, and methods to control and reduce glare.

1. Ugr lighting meaning and Glare Value Calculation

• Definition:The UGR is a unified glare evaluation system introduced by the International Commission on Illumination (CIE), used to quantify discomfort glare caused by high luminance contrasts in the observer’s field of view. The calculation formula for UGR is as follows:

UGR = 8 log₁₀(0.25 ∑ (Li * ωi * Pi) / Lb)

• Where:
  • L_i：= background luminance (in cd/m²)
  • ω_i= luminance of each glare source in the observer’s line of sight (in cd/m²)
  • P_i：= solid angle observed from the glare source (in sr)
  • L_b：= relative position index of each glare source.

Understand what UGR means

UGR range: UGR values typically range from 13 to 28, with lower values indicating less glare and higher visual comfort.

• UGR < 16: less glare and higher visual comfort.
• 16 ≤ UGR < 19: Glare is moderate and acceptable to most users.
• 19 ≤ UGR < 22: Glare is large and may cause discomfort for some users.
• UGR ≥ 22: Glare is very large and may cause severe visual discomfort.

2. Influencing Factors of Glare Value

• Luminance of the Light Source: The higher the luminance of the light source, the more significant the glare. Light sources exceeding 20,000 cd/m² typically require shielding to reduce glare.
• Position of the Light Source: Glare increases if the light source is closer to the observer’s line of sight, so the installation position and angle of the fixtures are crucial.
• Size and Number of Light Sources: Larger apparent surface areas and a greater number of light sources lead to increased glare. For example, large billboards can cause severe glare issues.
• Surrounding Ambient Brightness: Lower ambient brightness means the observer’s eyes adapt to lower light levels, making glare more prominent. Thus, transitional lighting design is crucial in road lighting.

3.Unified Glare Rating Standard Requirements

Office Environment UGR

UGR Maximum Value: 19

Comments: High visual comfort to avoid fatigue; ensure even brightness distribution.

Educational Environment UGR

UGR Maximum Value: 16

Comments: Prevent glare affecting attention and learning; appropriate fixture positioning.

Healthcare Environment UGR

UGR Maximum Value: 16

Comments: Provide good visual conditions for safety and comfort; minimize glare in critical areas.

Industrial Environment UGR

UGR Maximum Value: 22

Comments: Glare can affect efficiency and safety; consider equipment height and complex layouts.

Commercial Environment UGR

UGR Maximum Value: 19

Comments: Prevent glare affecting shopping experience; fixture placement in display and work areas.

Residential Environment UGR

UGR Maximum Value: 16

Comments: Warm and comfortable atmosphere; choose low glare designs.

Outdoor Environment UGR

UGR Maximum Value: 25

Comments: Impact on nighttime safety; install fixtures at appropriate heights.

Museums and Exhibition Halls UGR

UGR Maximum Value: 16

Comments: Clear and glare-free lighting to protect exhibits; low glare and directional lighting.

Sports Venues UGR

UGR Maximum Value: 22

Comments: Glare affects performance; ensure even distribution of light.

Transportation Facilities UGR

UGR Maximum Value: 25

Comments: Safety for drivers and pedestrians; avoid direct glare.

Theaters and Cinemas UGR

UGR Maximum Value: 16

Comments: Soft lighting enhances experience; low glare designs recommended.

Libraries UGR

UGR Maximum Value: 16

Comments: Comfortable reading environments; avoid direct glare on readers.

Hotels and Restaurants UGR

UGR Maximum Value: 16

Comments: Enhance guest experience with a warm atmosphere; low glare and dimmable lights.

School Laboratories UGR

UGR Maximum Value: 16

Comments: Prevent glare affecting safety; install fixtures above work areas.

Hospital Wards UGR

UGR Maximum Value: 16

Comments: Comfortable lighting promotes patient recovery; low glare design.

Airport Lounges UGR

UGR Maximum Value: 19

Comments: Clear and glare-free lighting for safety; appropriate fixture installation.

Retail Stores UGR

UGR Maximum Value: 19

Comments: Bright, glare-free lighting to attract customers; low glare designs.

Factory Production Lines UGR

UGR Maximum Value: 22

Comments: Glare affects safety and efficiency; ensure even light distribution.

Parking Lots UGR

UGR Maximum Value: 25

Comments: Safety for drivers; avoid direct glare.

School Hallways UGR

UGR Maximum Value: 16

Comments: Ensure safety with comfortable lighting; avoid glare.

Public Buildings UGR

UGR Maximum Value: 19

Comments: Clear lighting for public safety; appropriate fixture placement.

Home Kitchen UGR

UGR Maximum Value: 16

Comments: Bright and safe lighting; avoid glare during cooking.

Home Living Room UGR

UGR Maximum Value: 16

Comments: Enhance leisure experience with warm lighting; choose adjustable systems.

Home Bedroom UGR

UGR Maximum Value: 16

Comments: Soft lighting for rest; utilize low glare designs.

These UGR maximum value recommendations are based on standards from the International Commission on Illumination (CIE) and best practices in the industry. Lighting designers should consider UGR values alongside other factors like illuminance, color temperature, and color rendering index for optimal lighting effects in specific scenarios.

4. Methods to Control and Reduce Glare

• Fixture Design: Utilize semitransparent diffusing plates or reflectors to reduce the brightness of the light source. For sources below 20,000 cd/m², using diffusing plates can enhance brightness distribution.
• Fixture Installation: Position and angle fixtures to prevent direct light from accessing the observer’s eyes. Installers should keep fixtures at an elevation angle of no more than 15° and ensure maximum light intensity directions have a vertical angle not exceeding 65°.
• Transitional Lighting: Adding transitional lighting at points of light-to-dark transitions can reduce eye adaptation time. For instance, transitional lighting should be installed between illuminated and non-illuminated road sections to diminish glare effects on drivers.

Evaluating Glare Control Effectiveness

UGR and Glare Control: UGR values can be used to evaluate the glare control effectiveness of lighting fixtures, allowing for the selection of appropriate fixtures and installation methods.

Maximum Allowable UGR Values: According to Dr. Einhom’s recommendations, the maximum allowable illuminance for diffuse or uniform indirect lighting at different UGR values are:

• UGR = 13: Maximum allowable illuminance is 300 lx.
• UGR = 15: Maximum allowable illuminance is 600 lx.
• UGR = 19: Maximum allowable illuminance is 1000 lx.
• UGR = 22: Maximum allowable illuminance is 1600 lx.

Choose the appropriate UGR value

According to the requirements of the use site and the user’s visual comfort demand, choose the appropriate UGR value.

• Office environment: UGR value is generally required to be no more than 19 to ensure employee visual comfort.
• School classroom: UGR value should be lower, usually no more than 16, to protect students’ eyesight.
• Home environment: UGR value can be relaxed appropriately, but it is best not to exceed 19.

5. Unified Glare Rating Special Applications

• Commercial Pedestrian Streets and Underpasses: Glare can be used intentionally to create a specific atmosphere such as glamour or vibrancy. For example, using a multitude of incandescent bulbs or LED strips can create flickering effects to enhance visual appeal. However, energy-saving and safety factors must still be considered to avoid excessive glare.
• Residential Areas: Lighting designs in residential areas should focus on comfort and safety, recommending fixtures with lower UGR values. For instance, using 30-50 watt LED fixtures with UGR below 13 can provide excellent illumination while minimizing glare on residents.

6. Real-World Case Studies

• A Major City Highway: This highway employs 100-150 watt LED fixtures with cutoff designs, maintaining UGR below 16. The installation angle is set at 15°, ensuring effective reduction of glare for drivers.
• A Commercial Pedestrian Street: This street utilizes 50-70 watt LED fixtures designed with semi-cutoff brightness, controlling UGR below 13. The positioning and angles of the fixtures are carefully planned, ensuring sufficient illumination while creating a pleasant visual environment.

7. Conclusion

The glare value (UGR) of solar street lights should be determined according to specific application scenarios and requirements. For major roads and highways, using cutoff or semi-cutoff fixtures with UGR not exceeding 16 is recommended; for secondary and local roads, fixtures with UGR below 13 are suggested. For sidewalks, commercial pedestrian streets, and residential areas, fixtures with UGR below 13 are ideal to ensure good visual comfort and safety. Through reasonable design and installation, glare can be effectively controlled and reduced, enhancing overall lighting quality.

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