What does UGR mean?

UGR stands for Unified Glare Rating. It’s a mathematical way of describing whether a luminaire is likely to cause glare.

What is glare?

Glare is the effect that occurs when two sources of light are present simultaneously in a person’s line of sight. An example most people will be familiar with is when the headlights of an oncoming vehicle at night make it very hard to see the road ahead. The same can happen in an office environment when badly designed lighting reflects off the computer monitor making it hard to see what’s on the screen.

Even when computer screens are non-reflective, the advent of high efficiency edge-lit LED panels has tended to result in higher illuminance levels, with all of the light delivered at the diffusing surface of the luminaire, not deep within a reflector / louvre system. The 100% direct illuminance from standard LED panels means the surface of the panels is very bright when compared to the background, giving glare!

How is glare measured?

The UGR rating is calculated using an equation:

UGR = 8 log [0.25/Lb Ʃ(L2Ω/p2)]

L represents the luminance value of the luminaire Lb is the value of the background luminance

Ω is the solid angle of the luminaire as seen by the viewer.

p is The Guth Index. This is a factor based on the likelihood of glare, known as Visual Comfort probability.

The Sigma sign (Ʃ) means that the equation includes ALL fittings within a space.

You can see from the above that a UGR calculation can only be accurate when applied to a physical space. It cannot be measured in a test room.

How was glare controlled before LED?

When desktop computers were first introduced there were serious problems caused by the reflection of light fittings in the shiny highly reflective screens. This was dealt with in two separate ways:

The monitor manufacturers started to produce non-reflective screens CAT2 fluorescent light fittings were introduced. These reduced glare by having a 65° cut-off.

Both methods have their own disadvantages:

Matte screens have a reduction in contrast and colour vibrancy, Slight to moderate reduction in sharpness – depending on thickness and layering of matte surface as well as monitor pixel pitch, Generally more difficult to clean due to dirt penetration, and Grainy or hazy texture apparent in some instances, particularly when displaying white and other light colours

The disadvantage of the CAT2 luminaire is obvious from the picture– it’s just ugly!

How is glare controlled on LED panels?

In a good quality LED panel, there are three main components behind the diffuser:

1. 1. LED strips that generate the light

A ‘Light Guide Plate’ that takes the light and directs it towards the diffuser

2. A reflective sheet that reflects stray light within the panel back towards the Light Guide Plate

The standard construction of LED panels results in a wide beam angle of 120°, and for some installations this can lead to UGR levels greater than those specified in BSEN 12464: 2002. The solution to this is a special diffuser that narrows the beam angle of the LED panel – just like the louvres on a CAT2 luminaire. An added advantage of this is that because the light is directed more to where it is needed, additional energy savings can sometimes be obtained.

 

What to know about UGR19 LED Panels

Also known as UGR<19 LED panels, these are designed to assist with obtaining a UGR19 rating in an installation, they are not a guarantee of obtaining it, as the UGR rating obtained is installation specific.

UGR ratings in actual installations

Recommended UGR ratings are shown below:

 

The actual UGR calculation is performed with software such as RELUX or DIALUX. The software is used to create a 3-D model of the room with lighting and considers many factors including room usage, room dimensions, room colours, luminaire mounting height, number of luminaires, amount of light from luminaires, light spread from luminaires (the less light spread then the lower the UGR), and the quantity of luminaires.

 

At LED Panel Store we are happy to offer a Relux Lighting Design Service – please call us on 01652 638850 or email [email protected]

See our full range of LED Panels, including UGR19 LED Panels here. 

Alternatively, read more about the recent campaign looking at “Where have the stars gone?”.