Light fixtures (“Luminaires”) are the hardware required to hold and operate artificial light sources; the layout of light fixtures is their arrangement in the room.
When complementing daylighting with artificial light, fixtures and layout can be as important to good lighting as the light sources themselves. Good fixture design and layout can distribute light well, separate task lighting from ambient lighting, provide good controllability, and even change the color of the light source.
Successful design of fixtures and layout is measured by testing visual comfort in the room for all activities in the room’s program, and measuring the amount of energy required to achieve good visual comfort thresholds. The less energy required for comfort, the better. Use manufacturers that publish luminous efficacy measurements for certain light sources in certain fixtures, to avoid guessing how fixtures will affect sources.
- Types of Luminaire
- Lighting Layouts
- The Lumen Method of Lighting Design
Types of Luminaire
Luminaires are the fixtures that house lights. They greatly affect both the brightness and the spatial distribution of the light, because they bounce and/or filter the light from their lamps, for different effects. Types of luminaires are generally categorized by their light distribution. Some common distributions are shown below: direct, semi-direct, and direct-indirect.
Types of luminaries
Spatial distribution from luminaires
Generally, light shining on task surfaces is “direct” light, while light shining away from such surfaces is “indirect” light. Sometimes designers instead describe fixtures based on the direction of the light: “uplights”, “downlights”, or “sidelights”.
The output distribution of a luminaire can be measured over a range of angles and plotted on a polar diagram. In it, the lines represent light levels actually measured at a fixed distance from the luminaire (usually 1 m) as it was rotated around to different angles. In most cases, the units of this graph will be lumens. However, these levels can be normalized from 0-1 to represent a multiplication factor instead; this provides for the use of different lamp powers in the fixture.
Types of Luminaire
(click to enlarge, see more detail in Building Science Fundamentals)
A luminaire refers to a complete lighting unit, including one or more lamps, reflective surfaces, protective housings, electrical connections, and circuitry. All these components affect the overall output of light from the unit. Even with a very bright lamp, translucent or semitransparent materials may reduce the flow of light, and reflective surfaces can quickly become dusty and dirty in some environments, also reducing output.
Given the wide choice of different lamps and luminaires available, there is an almost infinite set of different arrangements of electric lights within a room that will provide a certain illumination level.
The primary concern in lighting layout is to avoid glare on activity surfaces. Such glare is a result of light bouncing directly into user’s eyes, rather than diffusely.
Good and bad lighting locations, causing or avoiding glare
The ultimate choice of lighting layout will invariably be an aesthetic one— achieving the right feel or ambiance within the space. Doing this well comes from experience as a lighting designer and from simply applying a bit of thought to the space and how it is likely to be used.
The images below demonstrate just two of the many different ways of lighting a simple room to give exactly the same lighting levels on each work surface. Each layout has advantages and disadvantages. For instance, the first layout might use less energy, but the second layout will cause less glare and will have fewer shadows cast on work surfaces by occupants.
Different fixtures and layouts providing the same lighting levels with very different distribution