Indirect lighting represents a significant segment of the overall lighting market in North America. This approach to space lighting typically features fixtures suspended from the ceiling that distribute the light mainly upward, and lighting designers often combine indirect lighting with direct lighting, task lighting, or both. Indirect lighting minimizes glare on computer screens and creates a soft, inviting environment for concentrated work. The accompanying increases in productivity and occupant satisfaction are hard to quantify, but the benefits are significant. Indirect lighting also offers the potential to reduce energy use.

What are the options?

Fixture type Indirect lighting fixtures, which are suspended from the ceiling or mounted on a wall, distribute 90% or more of the light upward so it’s reflected off ceilings and walls. In contrast, direct lighting fixtures project 90% or more of the light downward. Lighting fixtures are also available that combine indirect and direct lighting (figure 1).

Figure 1: The ups and downs of lighting

Light fixtures may send all, or most, of their light downward (A), upward (B), or provide a mix of up and down lighting (C).
Figure 1: The ups and downs of lighting

Many designers warn against using only indirect lighting—it can lead to ceilings with too much light and create a comparatively gloomy effect underneath. By adding a portion of direct lighting to an indirect fixture, lighting designers can provide more lighting variety while retaining the low-glare benefits of indirect lighting. Occupants who work at a desk or computer screen benefit from the low glare of the indirect portion; those walking about appreciate the depth and contrast that the direct component adds.

Furniture- or partition-mounted indirect fixtures are available for open office environments, making indirect lighting viable in these spaces. However, there can be problems with the application of furniture-mounted indirect fixtures. In its Green Floors project, Natural Resources Canada found that mounting fixtures on wall partitions limited design and modification flexibility. The agency’s designers also found it difficult to control lighting according to space occupancy because two offices shared the partition lights. Low placement of the partition lights provided better light distribution, but created glare problems for tall occupants walking by.

Lamp type. Indirect and indirect/direct fixtures typically use T8 or T5 lamps with electronic ballasts. T5 lamps are thinner, more efficient, and offer a higher intensity of light output than their T8 predecessors. The high intensity of T5 lamps means that designers can place rows of indirect fixtures as much as 12 to 15 feet apart on ceilings as low as 9 feet—some manufacturers claim that the fixtures can be used on ceilings that measure 8.5 feet or lower—and still provide uniform ceiling illumination levels. With T8 lamps, the standard spacing is 10 to 12 feet, and ceilings must be at least 9.5 feet high—higher than most conventional office ceilings. Wider spacing means fewer fixtures, which reduces the overall cost for installation.

T5 lamps are available in two types: standard output and high output. The high-output versions put out almost twice as much light as a T8 lamp of the same length, and therefore the number of single-lamp T5 fixtures required in a given space can be cut almost in half compared with single-lamp T8 units. Thus, indirect lighting systems that use T5 high-output lamps can be less expensive than a T8 indirect system despite the fact that T5 lamps themselves are still more expensive than T8s, although not significantly in some cases. Single-lamp fixtures also boast an advantage over two-lamp fixtures because light distribution is easier to control with one lamp than two. T5 lamps can also offer better performance than T8s in enclosed fixtures and warm spaces because they’re designed for a higher operating temperature. T5 lamps are also easier to dispose of than a pair of T8s because there’s less material involved. But because T5 lamps come in lengths that are shorter than the standard lengths for T12 and T8 lamps, they can’t be retrofitted into existing T12 or T8 luminaires. Additionally, some designers warn that the high-output models may be too bright and that installers should avoid creating hot spots on the ceiling, which would lead to the very glare that designers are trying to avoid.

How to make the best choice

When selecting a lighting system, the primary consideration is whether it provides adequate lighting distribution and intensity necessary for the tasks that need to be performed. In general, indirect lighting—often with a portion of direct lighting, task lighting, or a combination of the three—provides the highest-quality solution. It’s also useful to compare the cost-effectiveness of direct and indirect lighting.

Use the Screening Tool for Indirect Lighting to compare up to three lighting alternatives; for example, compare direct lighting using T8 lamps with indirect lighting using T8 or T5 lamps. Remember that an indirect or indirect/direct lighting system can illuminate a space with lower overall light levels than a direct lighting system, so it’s possible to use fewer fixtures with indirect or indirect/direct lighting than with direct lighting alone. Installation time will vary with the type of luminaire and the configuration of the space, but indirect lighting fixtures generally take less time to install than a set of individual fixtures that provide equivalent light. The most important point of doing the analysis is to compare systems that provide equal-quality lighting.

What’s on the horizon?

The introduction of the T5 created a new challenge for designers of indirect/direct fixtures. The high intensity of T5 lamps can produce glare problems in an indirect/direct fixture, leading manufacturers to develop new means of reducing that glare. One product that addresses this problem is the waveguide, which adds a downward component to indirect lighting fixtures. This enables designers to use high-intensity T5 lights without creating excessive glare. A waveguide delivers light from a linear source along the length of the film, allowing the light to escape in a controlled manner (figure 2). The structure of the lens, along with the lamp and lens arrangement, allows the lighting fixture to provide precisely controlled lighting distribution patterns that deliver a uniform, low-glare pattern of light downward.

Figure 2: Waveguides soften the intensity of T5 lamps

An optical waveguide features an acrylic plastic panel with a semirefractive film on the bottom of the panel. A microscopic array of prisms on the film directs light in a uniform downward pattern, resulting in low levels of glare.
Figure 2: Waveguides soften the intensity of T5 lamps

Who are the manufacturers?

Here are some of the leading manufacturers of indirect lighting fixtures:

Neither this list nor any mention of a specific vendor or product constitutes an endorsement or recommendation by the authors, nor does any content in the Business Energy Advisor constitute an endorsement or recommendation, explicit or otherwise, of the technology-related programs mentioned herein.

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