UGR: luminaire glare

Low glare and comfort is one of the main requirements for modern lighting in commercial spaces and private apartments. To take into account the level of eye discomfort created by artificial light, the industry has introduced such a characteristic of luminaires as the Unified Glare Rating (UGR). Among manufacturers of professional lighting equipment in developed markets, it is more important than the Lm/W indicator.

Consequences of the glare effect on human health.

The problem of glare effects has never been as acute as it is now. The fact is that LED lights, which have become almost ubiquitous, create more intense directional light and have the highest light output of all previously known light sources.

In addition, both at home and at work we are constantly using smartphones, computers, TVs and other equipment with monitors, the glare on which irritates the eyes. Despite the fact that every year computer screens are becoming less susceptible to bright light, the problem is still acute. The negative consequences of high glare from light fixtures are:

• eye fatigue;
• loss of concentration;
• loss of productivity;
• irritability;
• headaches.

UGR calculation

UGR is calculated using a formula that takes into account a number of factors such as luminaire angle of dispersion, luminous flux, background brightness, probability of glare. The UGR value is measured on a scale of 10 to 30 units in increments of 13, 16, 19, 22, 25, 28. The lower the index, the less glare. For reading, writing, computer work, training, leisure, study, the recommended UGR value < 19. The more serious requirements are made to the quality of lighting in the room, the lower the value should be.

UGR is measured in special equipment, after which the program outputs UGR data obtained from different points and under different set conditions. UGR can be measured by the tabular method, but will be 100% relevant only in "standard" input conditions, which are very rare in real life.

The true UGR is quite difficult to measure, since it is not a characteristic of the luminaire itself, but reflects the overall degree of comfort in the room. It is influenced by a combination of factors, such as the total illuminance, the reflectance of all surfaces in the room, the angle at which the light source is viewed, the position of the luminaires and a number of other factors. Thus, the UGR of the same luminaire, even in the same room, is not static. It varies with different lighting scenarios and the degree of natural sunlight illumination.
The glare effect can be direct or reflected. It can arise not only from using luminaires with low glare protection, but also from improper design in terms of light placement and the position of workstations relative to light sources. As shown in the picture above, the same luminaire can have low and high UGR when mounted differently.

How to create comfortable lighting for the eyes

Reducing glare and UGR in the room is achieved by the following technical solutions:

1. The use of luminaires with a recessed light source, which eliminates direct and reflected glare effect, as well as creates protection against glare;

2. Using fixtures with a concealed light source and optics;

3. The use of diffuse lighting fixtures equipped with lenses that clearly limit the angle of diffusion and soften the aggressive light, making it softer and more uniform. In this case, the lenses must be of high quality, with the highest possible light transmission, and the LED must have maximum brightness. Otherwise the light output will be low. Low quality plastic lenses, which are more and more common recently, absorb up to 60% of the luminous flux of the diode, poorly coping with the reduction of glare;

As for office fixtures for Armstrong ceilings, it is better to choose ultra-thin panels with an end arrangement of LEDs. The glare in most cases will be lower than in the classic fixtures of great thickness with LED arrays, which shine not to the side, but from top to bottom. This is especially true in rooms where people often have to look up at the ceiling, such as dental offices, gyms during back exercises, etc..

4. The use of various antiglare accessories, such as Honeycomb and anti-glare glasses.

5. Using profile lights with high quality acrylic diffuser, which reduces glare. In conventional lighting fixtures do not put this because high-quality diffuser is much more expensive, and low-quality - absorbs a large proportion of the light flux and not profitable in sales.

6. Applying a functional approach to lighting planning.