Selecting the Right Lamp Type: Color and Efficiency

While the architectural lighting fixture may determine how the light is distributed in a space, the lamp type determines the type of light being distributed and the energy and material efficiency of the system. Fluorescent, compact fluorescent, halogen, high-pressure sodium and light emitting diodes (LEDs) are a few of the lamp types available in architectural lighting fixtures. Each lamp type offers a unique combination in terms of the color composition of the light they emit and the efficiency with which they provide it. Knowing more about each specific lamp type will enable a design team to choose the type of lamp that best fits the ambient and energy performance needs of the project.

Color Quality

The ability to see color is dependent upon the kind and quality of light available. The color of a sweater or piece of fruit that registers in the human eye is actually a reflection of the light in the space bouncing off of the object being examined. This explains why the same item will look different under different types of light. The same red rose that looks brilliantly red outside on a sunny day may look almost black under a low-pressure sodium streetlight at night.

The Color Rendering Index, or CRI, assigns each light source a value that describes how the light it emits compares in color quality with natural daylight, which is considered the gold standard. Natural daylight has a CRI index rating of 100. In comparison, low-pressure sodium vapor lamps, the popular monochromatic parking lot light sources that bathe objects in an unnatural yellow hue, receive a CRI index rating of 0. The higher the CRI rating of a lamp source, the better the color quality of the light it creates.

Both halogen and incandescent lamps top the CRI rating scale, both receiving ratings of close to 100, however the light output from halogen lamps actually appears whiter and brighter due to a higher concentration of blue and green wavelengths in the light output. Technological advancements in other lamp types have significantly improved the CRI ratings that can now be attained with other lamps.  For example, fluorescent lamps are now capable of providing light with a better color quality than the cool white light (CRI rating 62) with which they were synonymous for so many years. Fluorescent lamps today can provide light with a color quality rating that ranges from 52 to 95, depending upon the specific lamp being considered.  The CRI rating for a Standard Clear high pressure sodium lamp may be as low as 21, but the rating can be as high as 70 for the Improved Clear or Color-Improved Diffuse-Coated lamp varieties. Clear metal halide lamps can be found with a rating of 65 and phosphor-coated metal halide lamps can receive a rating of up to 70. Phosphor-converted LED lamps can also score relatively high on the CRI scale with a range of 70 to 90+.

Technological advancements in lamp types have significantly improved the CRI ratings that can be attained by a variety of lamp types.
Lamp Type	CRI Rating
Incandescent	100
Halogen	100
Fluorescent	52—95
High-Pressure Sodium	21—70
Metal Halide	65—70
LED	70—90
Low-Pressure Sodium	0

 

Selecting a light source with a higher CRI rating will protect the integrity of the appearance of the merchandise or food under the illumination.

Efficiency

Two different factors are considered when determining the overall efficiency of a lamp type. Those factors are lamp efficacy and rated lamp life. The efficacy of a light source is measured in terms of the number of lumens produced per Watt (LPW). Higher ratios indicate more efficient light sources, because more light is being produced with less energy. Rated lamp life indicates the number of illuminated hours that one lamp is expected to last before needing to be replaced. Selecting a lamp type with a longer rated life will minimize the necessary maintenance and the material lamp waste created throughout the life of the system.

Fluorescent

The efficacy of a fluorescent lamp is dependent upon many different factors including lamp color and lamp length. These lamps can produce a range of 30 to 110 LPW, making their efficacy three to seven times higher than an incandescent lamp source. It should be noted that fluorescent lamps are affected by extremes in ambient temperature. Optimal operation will occur at temperatures between 5 and 25 degrees Celsius. Below this range there is a rapid drop in light output and efficacy. The rated lamp life for a linear fluorescent tube is between 7,000 and 24,000 hours, depending upon the specific lamp style selected.

Compact Fluorescent Lamps

Compact fluorescent lighting (CFL) consumes up to 75 percent less energy than incandescent lights and generate 50-70 LPW. The lamps last up to 10 times longer than the incandescent standards, illuminating areas for almost 10,000 hours per lamp.

Halogen Lamps

Producing 15-20 LPW and offering a much longer lamp life (between 2,000 and 4,000 hours), halogen was more efficient in both energy and materials than the incandescent bulb. As an added bonus that maximum efficacy is maintained throughout the life of the lamp.

Today, halogen lamps are available in a variety of lamp types. The two most common halogen lamp types are a parabolic aluminized reflector (PAR) and a multi-faceted reflector (MR). Both lamp types produce a significant amount of heat while operating.

Metal Halide Lamps

Metal halide lamps offer a better efficacy (70 to 115 LPW) than compact fluorescent, halogen, and incandescent lights. This lamp type requires a ballast to provide proper starting and operating voltages, which contributes toward the higher price tag often associated with metal halide fixtures. However, the higher initial cost is balanced by a low cost of ownership. Metal halide lamps will provide more light on a project, more efficiently, and for a longer period of time (rated lamp life ranges from 5,000 to 20,000 hours) than the less costly halogen alternatives.