Glare and UGR

When you searching the luminaires to set up or upgrade your lighting system, some of the seller may indicated with “UGR<19” as one of the key feature for their products. But what UGR is and why UGR should be less than nineteen? It seems too strange to make sense as most people do not have a deep understanding of UGR as it is the acronym of unified glare rating. This post will show you the basic knowledge about UGR. Hope it can help you understand UGR better and purchase the fixtures that meet all your requirements.

Glare

To comprehend UGR easier, let’ s talk about what is glare at first. Glare refers to the visual conditions that cause visual discomfort and reduce the visibility of objects due to unsuitable brightness distribution in the field of view, or extreme brightness contrast in space or time. There is a sense of light in the visual field that the human eye cannot adapt to, which may cause disgust, discomfort or even loss of clarity. Nevertheless outdoor or indoor, glare appears anywhere. For example, glare will be generated by the high beam of a coming car. A luminaire with excessive brightness will also cause glare at office or at home.

Glare can be divided intro discomfort glare and disability glare.

Disability glare is the glare that will decline visual effect and visibility which is generally come with discomfort. It is caused as the high-brightness light source in the field of view entering the eye, scattering in the eye and causing a decrease in the clarity and contrast of the object image on the retina.

Discomfort glare is often caused by improper lighting distribution or over brightness lighting source on the visual field. Discomfort glare normally will not do harm to visual function, but people will feel uncomfortable.

Long-term exposure to glare can cause visual fatigue and damage to one's eyesight. In addition, the glare is very annoying as it often causes people to feel anxiety, lack of concentration and other psychological discomfort. It would cause serious insomnia and headaches even worse.

UGR

UGR (Unified Glare Rating) is a measure of the glare from all visible luminaires indoors adopted by CIE (International Commission on Illumination). It is a psychological measure of the subjective response of the light emitted by a lighting device in a visual environment that causes discomfort to the human eye. UGR is not a mandatory regulation, but an industry standard formulated by CIE to create a better lighting environment and protect the health of consumer.

We need to emphasize two points. First, UGR is used for measure discomfort glare, not disability glare. Secondly, UGR scales the discomfort glare indoors, not outdoors.

It is not difficult to learn about why UGR is a measure for discomfort glare. Simply because the luminiaires that with disability glare are not qualified and will do harm to eye and health. There is no need to consider disability glare if you purchase the qualified luminaires. The reason for UGR scales the discomfort glare indoors is related to the measurement of UGR. All glares are annoying. What we need to do is to minimize UGR and then offer a more comfortable lighting experience for customers.

How to calculate UGR

UGR is calculated by a formula which includes a number of factors may affect glares caused by a luminaire. It ranges from 5 to 40. The lower the number, the lesser discomfort glare. The formula is as follows.

L: The luminance value of one luminaire

Lb: The value of the background luminance (cd/m²)

ω: The solid angle of the luminaire seen by the viewer

P: The Guth position index. Based on the likelihood of glare, also known as Visual Comfort Probability

Σ: The sum includes all the luminaires located within the area.

The formula seems to be precise as it requires the accurate value of each parameter, but it is hard to work with when it comes to reality. The parameters are difficult to measure. Thus, UGR is calculated by professional lighting design software like Dialux.

To put it simply, total lumen, lighting beam angle, and lighting surface area are three main factor affect UGR. It is concluded as:

• Higher lumen with higher UGR
• Smaller lighting beam angle with lower UGR
• Bigger lighting surface area with lower UGR

The UGR value exceeds 28 is unbearable for most of people while 19 to 22 is endurable. For workplace and classroom, the UGR value ranges from 16 to 19 is acceptable. If the URG values from 10 to 13, the glare is barely perceptible.

There is a simplified recommendation table for different workplaces or rooms as following.

Of course, just getting this table is not enough, because it is not always accurate. From the formula, we can know that UGR is apply to lighting installations, not fixture fitting. As UGR is calculated by software which simulates lighting installation in a standard room, the values can not represent reality situations. There are many other factors that affect UGR, such as the size of the luminous surface, luminous intensity, type of light distribution, etc.

Therefore, the luminaires described as “UGR<19” means this type of luminaire has a lighting distribution with UGR less than 19 in a specific space designed by manufacturer. The space is in pre-determined size and certain height from viewer to luminaires. In sum, the UGR value can be used as a reference for whether and how likely we would feel discomfort by the glare in specific environment , but it is not necessarily accurate in the actual environment.

How to minimize UGR

We have known that the luminaires in high UGR value would causes anxiety, lack of concentration and other psychological discomfort. It can even cause serious insomnia and headaches. In this case, what we should do is to minimize UGR during design and installation of luminaires. As mentioned previously, total lumen, lighting beam angle and lighting surface area are three main factors that influence UGR. Therefore, methods to reduce UGR are as follows:

• Decrease total lumen
• Use decoration materials in low gloss for surface
• Avoid installing lamps in interference areas

AGC always focus on offering a better lighting effect to our clients. We offer a solution to minimize UGR in a acceptable and more comfortable range. We use engineered grille textured lens to change the lighting distribution. The picture below shows the huge difference with different glare condition. More information on our LED solutions, please contact us.