lighting: What makes a well-lighted space?

Building Operating Management, Mar 2005 by Heinmiller, Glenn

Lighting is frequently taken for granted, creating problems for occupants and increasing costs. The fact is, some lighting is good and some is not. Employees aren't expected to be comfortable and productive working in a cold room or sitting on uncomfortable furniture, so why should anyone expect them to be comfortable and productive working under bad lighting?

When it comes to good lighting, what most people think about first is quantity. But quantity is only one component of good lighting, and it is just the beginning. After a certain minimum lighting quantity is reached, other factors become much more important. The minimum depends on what light level is needed - a moonlit night or an operating room both offer appropriate light for different situations. The point is more is not always better, and too much light usually is just a waste of energy.

LOOKINGMORECLOSELY

Because lighting quantity, measured in footcandles, is easy to ascertain, it is often used as a measure of lighting quality. But simply looking at light levels on the horizontal work surface says nothing about the quality of the visual environment.

Another key factor in determining lighting quality is glare. In spaces where people spend long periods of time or have important visual tasks to perform, glare sources should be eliminated. Glare occurs when something is so bright relative to the rest of the environment that it causes discomfort or reduces a person's ability to see.

In the 1980s and 1990s, concerns about glare focused on reflected glare from computer screens. With the advent of flat screens with low-reflectance coatings, this is no longer a significant issue. But glare is not just limited to sources directly in front of a person. Recent studies have shown a person can perceive glare sources from directly above, known as overhead glare. Glare sources of concern in offices today are lighting fixtures themselves, windows and direct sunlight.

The quality of light is not determined solely by the sources of direct light. Research indicates that, in spaces like offices and classrooms, bright walls and ceilings are preferred and increase comfort. When room surfaces are perceived to be too dim, a space can feel dark, regardless of the light level on the task.

One way to make rooms feel brighter is to light ceilings and walls with indirect light sources. Those surfaces become the light source for the room, and the lighting is even and glare-free. It doesn't have to cost more to light walls and ceilings: Light levels can be reduced, and the space will still be perceived as bright.

The fixture type most commonly used for indirect lighting in most spaces is the pendant linear fluorescent uplight. These come is all shapes, styles, output and prices.

Be aware, however, that when the ceiling is less than 9 feet high, pendant fixtures become a problem because they might hang too low. In open offices where furniture plans are fixed, one way to solve that problem is to hang the pendant linear fixture above the spine of the cubicles where no one will walk. Over furniture, fixtures can be hung as low as 6 feet, 6 inches and still be above eye-height. Furniture-mounted uprights or fixtures built into hard partitions or casework are other possibilities.

A hot trend in office lighting is the use of so-called "recessed indirect" fixtures. These are typically 2-by-2 or 2-by-4 fixtures with a perforated basket in the middle concealing the lamps that cast light up to a curving white reflector. Although these fixtures look better than the generic parabolic or lensed troffers, they can be a source of glare. Bright fixtures in the ceiling are not a substitute for indirectly lit ceilings, especially in large open areas.

NOT TOO MUCH, NOT TOO LITTLE

Another important factor in lighting quality is brightness balance. The relative brightness of various surfaces in the field of view must not be too different. In an open office environment these surfaces can be categorized as the task itself, the task's surrounding area, such as desk and cubicle partitions, and room surfaces, such as walls, ceilings and windows. Too much difference can cause eyestrain and discomfort. In an office, the task is often self-illuminated: the computer screen.

The brightness of a surface depends not only on how much light is falling on the surface, but also on the reflective properties of the surface material. A room with white walls will feel completely different than a room with dark wood paneling, even with the same amount of light falling on the walls in each. In office and classroom environments, dark partitions and walls should generally be avoided because they can produce contrasts that are too high and spaces that feel dark. Light-colored walls and partitions make spaces feel bright and help distribute light around the space, filling in shadows and making minimum light levels easier to achieve.

Given the preference for indirect lighting, it might seem logical to conclude that uniform lighting is the key to quality lighting. But some designers believe that totally indirect lighting is too bland and featureless, like an overcast day. A bit of direct lighting creates a little shadowing and reflects off shiny objects creating highlights and depth.