Make Light Work of Office Lighting with LEDs
Office lighting is more complicated than one may think at first glance. It needs to do the obvious, provide lighting, but it should also accomplish several other tasks as well.
Properly designed office lighting provides visual comfort, enhances worker performance, and helps keep employees safe.
And, in addition to doing these things, if you use LEDs, in a well-planned manner, good lighting can also reduce a building owner’s operating costs. How do you accomplish this, you may be wondering. Just read on to find out.
LED Office Lighting 101
Here’s everything you need to know to deliver office lighting that exceeds the standards.
One of the most important things to be knowledgeable about when designing a lighting plan is your desired light levels.
We measure these in foot candles, as opposed to lumens because foot candles represent the amount of light that reaches a surface area ( like a desk or workstation) and lumens measure the amount of light leaving a fixture.
A foot-candle is defined as one lumen per square foot. Our free lighting plans is a great tool for determining ideal light levels and discovering how to achieve them.
Lighting plans will also show you how balanced and even the light is throughout the space.
In addition to achieving a specific light level, office lighting should have an even 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. And, it’s the way we determine how evenly light is distributed in a space.
For an office setting, we recommend aiming for a ratio of at least 0.60. This is the minimum level at which employees won’t notice a difference in lighting levels.
However, raising the ratio to 0.65 will greatly improve uniformity and help those who have less than perfect vision.
Regardless of the intended use, one of the goals of lighting is always to reduce glare. Lighting should be an asset to space, but when there’s glare it becomes a headache, quite literally.
And although reducing glare is important in any setting, it’s especially important for office lighting. Typically, in an office environment, the majority of the employees will be spending an eight-hour day beneath lights, staring at computers.
This is extremely exhausting to the eyes, and though it may sound trivial at first glance, can become quite serious and result in severe vision problems. In order to avoid eye fatigue, headaches, and neck & shoulder pain you must have 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 a phenomenon caused by bright light sources or extreme brightness contrasts in someone’s field of vision.
Glare is most often caused by reflective surfaces and will be present around things like, windows, glossy magazine pages, computer screens, or incorrectly designed and installed lighting.
There are two types of glare, direct glare and indirect 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. And, despite being an indispensable tool, they do cause some problems.
Computer screens can produce something called indirect glare due to their bright, shiny surfaces.
This can cause users discomfort and facilitate the development of vision problems. In order to prevent this, there is a maximum luminance limit for downward pointing fixtures, 1500cd/m2 for medium luminance screens, and 3000cd/m2 for high luminance 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 different varieties of glare, although they often 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 measured by the Unified Glare Rating (UGR). UGR is the method that’s used to calculating glare from light fixtures, sunlight that penetrates through windows, and other bright lights.
The UGR rating helps to determine how likely a light fixture is to cause visual discomfort to those in view. UGR classification ranges from 5 to 40 with 5 representing the least glare and 40, the most.
In office settings, we suggest maintaining a UGR under 19. But in the less occupied areas, like corridors and break rooms, the UGR can range somewhere between 19 to 25.
However, if there are many elderly people in the area, we suggest a significantly lower UGR value of 16, specifically if they will be writing, reading, or performing typing activities.
Illuminance on Walls & Ceilings
In the same way that the illuminance of a task area is important, the illuminance of the surfaces that surround it also has a significant impact on visual comfort.
Generally, for an office setting, we recommend that the illuminance values for walls be around 5 fc lux and illuminance for ceilings as 30 lux.
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.
Although it may have once been acceptable to decide how many lumens you wanted and then space fixtures around the room to achieve the desired light levels, that’s no longer the case.
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 with our free photometric lighting plan, but we’ll also outline how you can estimate it yourself, 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
Where E is the average illuminance in fc, Lu refers to the s the number of lumens, and A is the area in square feet.
Using the exact number of fixtures in an area, the different types, and the number of bulbs installed in each light, you can determine how many lumens the lamps generate by multiplying the entire initial lamp lumens by the initial lumens per lamp.
But, this number isn’t entirely accurate. Not all lumens reach the floor, and therefore not all lumens are applicable.
To account for this, you’ll need to find an element that expresses the ratio between the lumens reaching the work plane and the overall lamp lumens produced.
This is known as the coefficient of utilization (CU).
Recommended Illuminance Levels
To determine the non-uniform lighting needs of your space, you will first need to start with a uniform lighting measurement and, after that, use additional formulas to account for aspects such as lighting cavities and obstructions.
This is what the Illuminating Engineering Society of North America recommends.
The lumen method enables you to figure out the anticipated degree of uniform illumination on a fictional horizontal plane, at about 2.5 feet beyond the floor, which is the average desktop height.
Coefficients of Utilization
CU is the percentage of lumens that leave the fixture versus those that actually reach the work surface. Unlike the equation above, this describes light that directly leaves the fixture and light that is reflected. This is affected by several different things.
- The type of a lighting unit, its efficiency, and pattern of distribution.
- How reflective the room’s surfaces are. The more reflective the ceilings and walls are, the more likely it is that the lamp lumens will get to the work surface.
- The height at which the light fixtures are mounted. The higher the fixtures are mounted, the bigger the wall space between the light and the work surface is. Consequently, the more chances there are for the walls to soak up the light.
- The room’s size. The bigger the room is, the more lights you’ll need. This means more light overlap, which means a higher light level. A larger room also provides fewer opportunities for light to be absorbed by the walls.
- The room’s proportions. Weird 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.
From the second a light fixture is turned on, it will begin to lose lumens. This happens with all bulb types at all rates, with LEDs having the longest consistent lumen lifespan.
Because of this, you’ll need to aim for a primary illumination level that’s higher than the minimum specified level.
The light loss factor (LLF) is the cause for this reduction in quality.
The light loss factor is the proportion of the lowest illuminance level before any restorative action is taken, like replacing the lamps, to the primary light level.
LLF is the end result of all factors that have a role in the loss of light. These factors are categorized into two groups: unrecoverable and recoverable.
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.