What is UGR?- Everything You Need To Know About Light Glare

What Is UGR?

Light glaring is a common phenomenon but a very disturbing fact. So, to track this glare and have a comfortable light setup, a unified glare rating (UGR) is a crucial light matrix. It considers the brightness of the light, the dimension of the room, and other factors to give you a predicted glaring rating.

Thus, while purchasing any light, you can pre-determine whether this fixture will cause any glaring issues or not. For indoor uses, a low UGR rating is best; you will get a comforting light.  But if you see high UGR values in the specification, it means the light tends to cause more glaring. But it necessarily doesn’t mean the fixture is not good enough. High UGR lights are used in applications requiring high brightness over a large area.

Therefore, you can say UGR is not a constant term or fixed property of any fixture. It in fact differs for the same bulb due to changes in viewing angle, observers’ position, size/height of the room, etc. Therefore, to get the correct UGR of a fixture, you must consider its surrounding environment and position.

Form of Glare

a. Disability Glare

Have you ever got blanked while driving at night as the bright headlight flashes strike your eyes? This temporary washout of vision is called disability glare. When a sudden light of high intensity falls on your eye, it scatters within the optical system of the eye. As a result, you no longer can see the object clearly. You will face such disability glare when there is an unbalanced consistency between the object and the background.

b. Discomfort Glare

Discomfort glare doesn’t relate to the visibility of an object. Instead, it refers to the irritation or discomfort as strong light rays fall into your eyes directly. Discomfort glare depends on the brightness of the light source, its location, size of the glare, etc. Besides, this also varies from person to person. For instance, you and your friend are sitting side by side. You may find the lighting on the sidewalls glaring at you. But the friend who is shorter/taller or sitting at a different angle may not find it uncomfortable. Thus, discomfort glare varies for age, eye health, and physical and mental state. 

Type Of Glare

1. Direct Glare

When a light ray falls directly into your eyes, it’s called direct glare. This is caused by the high brightness of the bulb falling in the field of your vision. From the vertical surface, the angle of direct glare ranges from 45° ~ 85°.

2. Reflected Glare

Before getting to a formal definition, let me clear the concept of reflected glaring with an example. Think of a bright light reflecting on the mirror and flashing directly to your eyes. Do you find the lighting comfortable? Of course not, right? This is what a reflected glare is. This occurs when the light source is reflected back to your eyes, usually from a shiny or polished surface. This can be the wall, floor, mirror, or ceiling of your room.

3. Background Glare

When you can’t clearly see an object due to too bright background lighting is what we call background glare. For instance, you have a big window set behind the TV. The bright sunlight coming through the window causes glare issues to dominate the TV screen. Thus, you won’t enjoy watching the TV, the light from outside will continuously hit your eyes.

UGR Rating & Range

Based on the glaring effect of a fixture, the UGR ranges from 5 to 40. If you want to have glare-free lighting, choose a fixture with low UGR. This allows you to work comfortably without causing eye strain. In contrast, a high UGR> 28 will cause you excessive glaring issues.

Importance Of UGR

Who likes a bright light staring boldly right up your eyes? It is not only irritating but also affects your health and wellness. So, what’s the solution? Simply consider the UGR rating and install the light at the right location using the proper strategy. This will bring you the following benefits:

1. Comfortable Lighting

You can’t let go, considering UGR for glare-free, comfortable lighting. Suppose you just got a random fixture for your study room and installed it at such a location that it directly hits your eyes. In such a situation, can you concentrate on your study? Of course not; the bright illumination from the light will distract you. To get rid of this, go for lights with a low UGR rating.

2. Boost Productivity & Performance

A glaring light not only causes irritation, it further affects your productivity. You can’t sit on your desk for longer with full concentration. This eventually slows down your task and hampers productivity. But if you consider the UGR rating while installing the light, you won’t face such issues.

3. Health and Well-Being

Eye strain and headaches are common while you are facing a glaring light for too long. This can also lead to stress and migraine issues. So, you definitely won’t risk your physical and mental health for a glaring fixture, right? The best thing you can do is go for planned light designing and low UGR fixtures.

How Does UGR Work?

UGR is actually a calculation of measuring visual comfort under a definite light fixture. It considers several aspects of the bulb and the room in which you will install it. This includes the brightness, size, and height of the light from the ground. Next, the features of the room, such as height, length, width, and reflective surfaces, are also included in the calculation.

This doesn’t end here. To get a closer result of the light’s glaring effect, the UGR area is measured from different viewing angles: crosswise and endwise. Thus, by considering all these aspects, UGR gives you a glare rate for your bulb of a specific location.

Factors Affecting UGR

Brightness Of The Light Source

Place two lamps, one of high brightness and another of moderate level, on your study table. Which lighting do you find more comfortable while reading on your desk? As the table lamps are placed on the table and the distance between the light and the table surface is small, too bright light will surely be bothersome. The value of UGR for this bright light will be much higher than the one with low brightness. So, what you learn from this example is that the brightness of the light source has a greater effect on UGR.

Size & Height Of The Room

Suppose a light from UGR17 is installed in a big room with a high height. When you place the same fixture in a small room with a lower height, the glaring rate can change to UGR19+. Thus, with the increasing or decreasing area and height of the room, the UGR also changes.

Reflected Elements In The Room

Usually, a ceiling reflection of 70%, a wall reflection of 50%, and a floor reflection of 20% is considered the standard for a room with a dimension of 4H/8H. However, with the change of reflection percentage, the UGR values also change.  The below chart will clear this up:

Angle Of View

If the light source is installed directly above or at a sharp angle from you, it will cause glaring issues. Here, the light falls at your eyes at direct angles; so the UGR will be high. However, by changing your position, you can minimize the light angle of the incident and thus reduce the UGR.

Eye Condition Or Visual Acuity

If you have myopia, that is, you can’t see distant objects clearly, and you tend to face more glaring issues. The same will happen if you have dry eye syndrome or photophobia. Besides, with aging, the adaptation capacity of the yee also reduces. So, the same light setting may not appear discomfortable to you, but an old man might find it too bright. That is, though the value of UGR remains constant, its perception varies from person to person.

How is UGR Calculated?

Method 1: Application-Based UGR Calculation

The application-based UGR calculation deals with real-time evaluation of the light. In this method, you have to place the light in the exact location where you plan to mount the fixture. Next, place observers on different points and calculate the glaring rate.

For UGR calculation, follow the below formula:

To find out these values, you will find different professional software that measures light. The most common applications are Dialux, Relux, and AGi32.

Method 2: Luminaire Base UGR Calculation

This method is popularly known as tabular method. It is a well-recognized method standardized by CIE. In the luminaire base UGR calculation, you will get 190 different UGR values for different room sizes and reflection combinations.

The room dimension is considered as the multiple of the height (H) of the room. For instance, a room of 4H/8H dimension means if the height of a room, ‘H,’ is 2.5m, its length is 4H = (4 x 2.5) = 10m, and width = 8H = (8 x 2.5) = 20m. In the tabular method, the room dimension is limited between 2H to 12H.

The calculation here is done from the viewpoint of a single observer placed at the center of the wall 1.2m above the floor. However, the observer must consider the view from two angles- crosswise and endwise.

How To Read  UGR TABLE DATA in the Test Report?

The UGR table data includes different factors to find out the glare rating of a fixture. To read the test report, here are some terms you must be familiar with:

Reflective Characteristics of the Room

The UGR table data features three reflective aspects of the room in percentage; these are:

1. Ceiling/ cavity: Amount of light reflected by the ceiling of the room. This usually ranges from 30% (0.3) to 70% (0.7). For light or white ceilings, the percentage is higher, and for dark ceilings, the reflection is lower.

2. Wall: Amount of light reflected from the vertical surface or walls of the room. The light reflected percentage for walls mostly ranges from 30% (0.3) to 50% (0.5).

3.  Working plane or floor: Amount of light reflected from the working surface or the floor.  This is the horizontal surface for considering the reflection of light. To calculate the UGR value from the position of the observer, you must consider this plane.

Room Dimension

The dimensions of the room are usually referred to as x, y, and H.

Here,

• x = Length of the room
• y = Width of the room
• H = Height of the room

In measuring UGR, the length and width of the room are determined as multiple of height, H. For instance, if you find in the report x = 4H and y = 2H, it means the length of the room is four times its height, and the width is two times the height.

Viewing Perspective or Angle

In the UGR report, the glaring is measured from two viewing angles or perspectives; these are as follows:

a. Crosswise View

The UGR ratings under this section mean that the observer got the view from the side of the room. That is, the fixture is installed along the length of the ceiling, and the observer gets the view from a sidewise direction.

b. Endwise view

The UGR rating under the endwise view is measured by placing the observer at the end of the fixture. That is, the observer was looking at the length of the light.

Likewise, by taking the crosswise and endwise view for different room dimensions, a total of 190 UGR ratings are listed on the test report.

Space-to-Height Ratio

The space-to-height ratio determines the distance between the luminaries. It is symbolized as SHR. The most permissible ratios of SHR are 0.25 and 1. The value of UGR differs for changes in this value.

How To Reduce the UGR of an Installation?

Use diffusers: In most cases, you will find high brightness is the cause of high UGR. To solve this, try out diffusers. This will distribute the light evenly without concentrating it in a definite direction. Thus, the UGR will be reduced to a greater extent.

Install decorative materials on the glossy surface: The reflection of lights from glossy surfaces causes direct glaring. So, place decorative items on the reflecting surface to create a barrier. This will minimize reflective glaring tendencies.  For example, placing a curtain on the mirrors will lower glare.

Adjust the placement of the luminaries: having adjustable lights, for instance, a track light? If yes, controlling UGR is in your hands! Change the direction and angle of the light and see if you still feel the same glaring as you felt before. This way by adjusting the light location, you can minimize the UGR for a definite direction or viewing angle.

Combining natural lighting with artificial light sources: when the light falls from a single light source, the intensity from that particular direction is high. This ends up causing high UGR. What you can do is to add multiple lights. This will divert your concentration from a single source and give you an even light output from multiple fixtures. Let me share another tip- instead of using one high-lumen bulb, always go for multiple medium-range lumen lights. This will provide you with a far more comfortable light setting.

Use light controllers: Want to get greater control over your lights, UGR? Install lights with a controller. This allows you to adjust the brightness and CCT as per your comfort preference. So, if you find the light too glaring from any position, simply reduce its brightness. This will reduce the UGR to some extent.

Guide To Choose The Right UGR Rating For Different Applications

Low UGR is crucial for fine tasks or activities that require the highest level of concentration. For example- in an operation theatre, a high UGR light can lead to a severe accident. So, for such an application, a UGR of 10 to 13 is applicable, which you can barely perceive.

Again, for retail and commercial stores, a UGR ≤ 19 is good. However, you must also consider the size of the space. For example, in large shopping malls that require high-lumen bulbs, considering a UGR ≤ 22 is acceptable.

In the below chart, I have added some UGR for various applications:

However, following these isn’t enough. To get accurate results, you must calculate the UGR by using the above methods, as I discussed above. Also, the lumen rating of the fixture, the height of the installation, and the size of the space matter.

What is a UGR<19 Light Fitting?

UGR< 19 light fitting means a light fixture that produces a UGR less than 19. However, it is applicable only for a fixed dimension of the room and percentage of reflectance values. This is because UGR< 19 is not a property of the light; under different environmental conditions and positions, the value will vary.

The standard measurement of a UGR<19 light fitting is considered for the specific specifications:

Dimension of the room = 4H/8H (‘H’ stands for height)

Degree of reflectance = Floor 20%, wall 50%, and ceiling 70%

However, in real cases, all rooms will not have such dimensions and reflections. That is why, to consider the glaring rating, you need to calculate it for specific applications.

How to Use UGR Glare Rating in Lighting Design?

While designing the light, you should purchase low UGR lighting for glare-free illumination. For this, you must consider the application to get the ideal UGR-rated bulb. For instance, if you are designing lighting for an office room, a UGR<19 is ok. But if it’s an operation room or place where tasks need to be done with full concentration, go with UGR 10 to 16.

Besides, check the UGR table to match the rating for a specific size of the room to get the accurate glaring effect. This will help you to position the light to get optimal illumination. Again, you must consider the reflective surfaces of the room while using light design. This can greatly impact the UGR value. For instance, the UGR for a bulb installed in a 4H x 2H room is 17.8, but due to an increase in reflection, this can reach 19+. So, you should do an application-based UGR calculation for real-time UGR value.

However, besides UGR, you should also get the right CRI and CCT of the bulb to get a finished light setup.

Standards And Regulation For UGR

BS EN12464 Light and lighting has covered UGR for more than 280 installation cases. This includes all types of applications, such as schools, offices, hospitals, industrial areas, and more. Here, you will find  UGR suggestions for both indoor and outdoor settings.

Below, I have summarized the maxim UGR suggested by BSEN12464 for interior areas, tasks, and activities:

Note: The UGR recommended by BSEN12464 is not mandatory to follow; it’s just a suggestion. For optimal light performance, design your lighting and pick UGR based on real-time application needs.

Limits Of the UGR Method

1. Limits of individual UGR data sheet values

The value that you get from the UGR data-sheet is not a constant value for a fixture. For instance, considering a standard room size of 4H/8H and reflectances floor 20%, walls 50%, and ceiling 70%, the UGR of light is 19. In real applications, the UGR can be higher or lower. 

2. Limits of the UGR tabular method

The UGR tabula method uses a virtual luminaire arrangement, not actual light lights. Besides, the room dimension in this method is limited between 2H and 12H. So, it doesn’t show a glaring effect for rooms bigger than 12 H or smaller than 2H.

3. Limits on the size of light sources

The UGR method is not applicable for light sources that cover a solid angle of less than 0.0003 sr or more than n 0.1 sr. So, if the big lights are located in giant halls with high heights, you can’t measure the glare effect with the UGR method. Thus, it is not applicable for wall washers, luminous ceilings, adjustable headlights (small), and other very small or very large luminous surfaces.

4. Limits due to age-related visual changes and vision correction aids

In the UGR method, the values are set based on average popularity. For age and individual eye condition, the UGR values vary; this limits its accuracy.

5. Limits for high spaces

According to CIE 117:1995, the UGR method is not applicable for high halls, e.g., from 7 m upwards. In this case, due to the large spot height, the observer sees the luminaries at small, solid angles. But even these small angles from a high luminous fixture can cause greater glaring.