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Office Lighting Design Guide
Upgrade Your Office Lighting with LEDs
Office lighting is more complex than you might think at first glance. It needs to do the obvious, provide lighting. However, it must also accomplish many other tasks.
Properly designed office lighting delivers visual comfort, enhances worker performance, and helps keep employees safe.
And, in addition to doing these things, when you utilize LEDs with a well-planned approach, effective lighting can lower a building’s operating expenses. How is this accomplished? Just read on to find out.
LED Office Lighting – The Basics
What follows is all you need to know to provide office lighting that goes above and beyond the standards.
Your preferred light levels are a significant thing to think about when you design a lighting plan. Light levels are measured in foot candles, not lumens because they signify the amount of light that reaches a surface (such as a workstation). Lumens, on the other hand, signify the amount of light that is emitted from the light fixture itself.
Lighting plans will also show you how balanced and even the light is throughout the space.
Office lighting must also have an even light distribution. To measure this, we use the term uniformity.
Uniformity is defined as the ratio of the minimum lighting levels in an area to the average lighting level in the same space. It’s the way we ascertain how evenly light is distributed in an area.
In an office space, we suggest targeting a ratio of at least 0.60. This is the minimum level at which employees won’t notice a difference in lighting levels.
Nevertheless, increasing this ratio to 0.65 will significantly enhance uniformity. This will benefit people who have substandard vision.
Regardless of the intended use, one of the goals of lighting is always to reduce glare. Glare can become a headache, quite literally.
Even though glare reduction is important in general, it’s especially important for office lighting. Typically, in an office environment, the majority of the employees will be working eight-hour days under lights while staring at computers.
This is extremely exhausting to the eyes, and though it may sound trivial at first, it can become very serious and cause severe vision problems. To prevent headaches, eye fatigue, and neck & shoulder pain you need a lighting plan that is designed to actively combat glare.
What Is Glare?
We know, we know. But bear with us, understanding what glare is and what causes it is key to reducing it.
Glare is an occurrence caused by bright sources of light or excessive brightness contrasts in a person’s field of vision.
Glare is usually caused by reflective surfaces and will appear around objects like windows, computer screens, glossy magazine pages, or improperly designed and installed lighting.
There are two kinds of glare, indirect glare, and direct glare. We’ll outline their differences below.
Indirect Glare and Display Screen Equipment (DSE)
These days, it would be extremely uncommon to find an office with only a few computers. They are indispensable tools, but they do cause some issues.
Computer screens can create indirect glare owing to their bright, shiny surfaces.
This can bring about irritation which creates vision issues. In order to prevent this, there is a luminance threshold for fixtures that point downward. The maximum is set at 3000cd/m2 for high-brightness screens, and 1500cd/m2 for medium-brightness screens.
Unified Glare Rating (UGR) – Direct Glare
As we discussed above, glare is a visual phenomenon that makes it difficult to see in bright light. There are two types of glare and they frequently overlap.
Direct glare is the type that actively affects your vision in a negative manner. It’s also the type of glare that will make you shrink away or turn your head.
This type of glare is assessed by the UGR (Unified Glare Rating). This method is used to calculate glare from sunlight that penetrates through windows, light fixtures, and other bright lights.
UGR determines the likely visual discomfort a light fixture will cause to those in its view. The UGR classification has a range of 5 to 40. 5 represents the least glare and 40 represents the most.
For office settings, we recommend keeping a UGR below 19. In areas that are less occupied, such as break rooms and corridors, the recommended range can be around 19 to 25.
However, if there are many elderly people in the area, we recommend a UGR value of around 16, especially if they’ll be reading, writing, or typing.
Illuminance on Ceilings & Walls
The brightness of surfaces surrounding a task area has an impact on visual comfort as well.
Generally, for an office space, recommended illuminance values are 5 fc lux for walls and 30 lux fc for ceilings.
In addition to this uniformity needs to be equal to or higher than 0.10. Typically, the higher the illuminance levels of the ceilings and walls, the more comfortable people will be.
Even though it might have once been adequate to determine how many lumens you wanted and then space fixtures around the room to realize your desired light levels, that’s not the case anymore.
Modern offices have distinct areas that require different levels of lighting. And, thanks to the introduction of computers, there’s glare to be concerned about as well.
Non-uniform lighting allows people to create customized lighting for the area depending on the intended usage and helps to save on power bills by reducing energy consumption.
You can plan for all of this easily by taking advantage of our free photometric lighting plan. But there’s also a way to estimate it yourself, as shown below.
The Lumen Method
The lumen method is formed on the description of a foot candle, or as we mentioned above, the lumens on an area of 1 square foot on which there is a uniformly distributed flux of 1 lumen.
This is shown in the equation below:
E = Lu ÷ A
In this equation, E represents the average illuminance in foot candles, Lu represents the number of lumens, and A represents the area in square feet.
Using the exact number of fixtures in an area, the number of bulbs installed in each light, and the different types, you can establish the number of lumens the lamps will produce by multiplying the initial lumens per by lamp the initial lamp lumens.
But this number of lumens isn’t completely accurate. This is because not all the lumens will reach the floor. Therefore not all lumens are applicable.
This can be accounted for by using an element called the coefficient of utilization (CU). The CU is the ratio of lumens that reach the work plane to the overall lumens produced by the lamp.
Recommended Illuminance Levels
To determine the non-uniform lighting needs of your space, you will first need to start with a uniform lighting measurement. After that, you can use additional formulas which will account for things like obstructions and lighting cavities.
This is what the Illuminating Engineering Society of North America recommends.
The lumen method allows you to determine the expected amount of uniform illumination on an imagined horizontal plane, at around 2.5 feet beyond the floor, which is the average desktop height.
Coefficients of Utilization
Coefficients of Utilization are the percentage of lumens that leave a light fixture compared to those that actually reach the work surface. Different from the above equation, this expresses light that is reflected and light that directly leaves the fixture. This is affected by several different things:
- The type of lighting unit, its efficiency, and pattern of distribution.
- The reflectiveness of the room’s surfaces. The more reflective the walls and ceilings are, the more probable it is that a lamp’s lumens will reach the work surface.
- The height at which the light fixtures are mounted. As the mounting height of the fixtures increases, so does the wall space between the work surface. Because of this, there are more opportunities for the walls to absorb the light.
- The room’s size. The number of lights that you’ll need will increase with the room’s size. This means that there will be more lights that will overlap. It also means that there will be a higher light level. A bigger room provides fewer opportunities for light to be absorbed by the walls.
- The room’s proportions. Unusual corners and narrow aisles will have a significant impact on CU.
Light Loss Factor
This is the last thing you’ll need to know in order to plan for non-uniform lighting distribution, and perhaps the most important.
A light fixture will begin to lose lumens from the second it’s turned on. This happens with all bulb types at all rates, with LEDs having the longest consistent lumen lifespan.
Because of this, you’ll need to target a primary illumination level that’s above the minimum specified level.
The light loss factor (LLF) is the cause of this reduction in quality.
The light loss factor is the proportion of the lowest light level before any corrective action is carried out, like replacing the lamps, to the primary light level.
LLF is the end result of all aspects that have a role in the loss of light. These aspects are divided into two classes: recoverable and unrecoverable.
About the Author
Cory Peterson is Director of Sales & Marketing at LED Lighting Supply where he focuses on improving customer experience and revenue operations. Cory writes about commercial & industrial lighting, along with topics important to contractors and facility managers. In his free time, Cory enjoys traveling, snorkeling, exercise and cooking.