Moodboard for entrance lighting. The picture shows among other things Focus Track.

UGR - UNIFIED GLARE RATING

WHAT IS UGR AND HOW IS IT CALCULATED?

The UGR method is used to calculate the degree of discomfortable glare in a symmetric indoor facility. Calculating according to the equation on the right,
a Unified Glare Rating (UGR) can be arrived at.

But don’t worry about this equation.
We calculate it for you.

WHAT DOES THE STANDARD SAY? 

EN 12464-1 refer to CIE’s tabulated UGR method when you need to carry out an evaluation of discomforting glare in an indoor lighting installation. The tabulated UGR method is based on the formula. To establish the glare rating in a lighting calculation the following is required: 

  • the room is rectangular and meets certain specific conditions regarding length, width and the luminaire’s mounting height. 
  • symmetrically placed luminaires  
  • symmetrical light distribution in the luminaire’s length and width 
  • only one type of luminaire to be taken into account  
  • no furniture in the room 


If the aforementioned requirements are not met you can use a product’s UGR table to see the glare rating. As luminaire manufacturers, we provide datasheets or tabular data*, so that you can quickly and easily establish the average glare rating per room. 
* The UGR tables for each respective product (those with symmetrical light distribution) are incorporated in the light data file and can be seen in the calculation program or calculation results. 

CAN A LUMINAIRE HAVE A UGR VALUE?

No, the UGR value does not belong to the luminaire but rather involves the its illuminating surface and the ambient light in relation to the observer’s eye and its position and angle. 

A rule of thumb is that intensive luminaires in dark surroundings give a higher UGR value while intensive luminaires in light surroundings give a lower UGR value.
 

Figure 1 Example of differences in contrast between dark and light backgrounds.

Differences in contrast between dark and light backgrounds

WHICH UGR VALUE SHOULD BE MET?

In the European standard, EN 12464-1:2011, there are UGR requirements for various visual tasks based on their difficulty, the recommended glare figures for UGR are provided in tables based on the task involved. UGR tables are provides in steps of 3, where 1 step is barely noticeable while 3 steps is perceived as a clear change in the glare. 

It is the level of difficulty in the visual task that determines what UGR requirement the workplace /room is given. Below is a simplified recommendation table, excerpts from the standard.
 

So the higher the requirement, the lower the UGR value!
Ref. no. UGRL Examples of area, task or activity
5.26.3 UGR16 Office: Technical drawing work
5.26.2
5.26.5		 UGR19

Office: Writing, typing, reading, data processing
Office: Conference and meeting room
5.2.1 5.27.1 UGR22 Common spaces in buildings: Cafeterias, serving rooms 
Retail trade: Sales area
5.2.4 UGR25 Common spaces in buildings: Cloakrooms, washrooms, bathrooms, toilets
5.1.1 UGR28 Communication areas: Communication areas and corridors

WHAT AFFECTS THE UGR VALUE IN A FACILITY?

A room has certain conditions that can’t always be influenced but nonetheless have an effect on UGR value.

  • Ceiling height/installation height
  • Room size
  • The ability of surface colour and material to reflect light

(See the standard values for reflectances on ceiling/wall/floor in the Light Template Indoors p. 8)

HOW CAN I AFFECT THE UGR VALUE IN A FACILITY?

You can affect the UGR value with the choice of luminaire and lighting. 

Tip!

  • Choose well dimmed fittings with hidden light sources or with anti-glare devices (feel free to evaluate visually)
  • Increase the luminosity of the room’s walls by illuminating them
  • Increase the luminosity of the ceiling by using luminaires with uplight