Begin each exterior lighting project by identifying the goals of the project. Whether highlighting architectural columns or illuminating a stone pathway, the lamp type will be determined by what the light needs to accomplish. Photo courtesy Tom Crane

 

Distribution

The area that the light illuminates from its source, also referred to as the distribution, varies from lamp type to lamp type. For example, metal halide lighting typically has a larger distribution than a MR16 halogen lamp. This is important because illuminating a forty-foot tree from the ground up and highlighting a shrub are two very different projects in terms of the distance that the light must travel and, subsequently, the type of lamp required to accomplish the feat.

In order to design an energy-efficient lighting system, the distribution capabilities of the light source and target area of the object must match. If the lamp selected does not appropriately reach the tree or wash the entire statue, it is not accomplishing the goals of the project.  If the lamp selected is more powerful or has a greater distribution than the space requires, energy may be wasted as unnecessary light is provided.  

Lumen Output

The amount of light produced by an individual lamp, also called the lamp output, varies from lamp type to lamp type. The lamp type used to create soft and interesting contrasts on an outdoor walkway will be different than the lamp selected to flood a space with security-level light when a potential intruder is detected.

Identifying the amount of light required in an outdoor space will help design teams select the lamp source that best matches the needs of the space, without supplying more individual fixtures or more light than necessary.  The application determines the source.

The Beam Spread

The beam spread of a light source describes the degrees of coverage or angle of the light it emits. Often characterized in terms of spot, narrow flood, flood, wide flood, etc., some lamps are capable of providing a variety of beam spreads, while others may be limited to one or two. The available beam spreads indicate the ability of the lamp source to appropriately meet certain design goals, such as spotlighting statues on the lawn or washing an entire boulder wall in light. For instance, beam spreads from linear fluorescent lamps are very wide.  An excellent choice for lighting large offices for overall lighting but not a good selection for projects requiring task lighting, a spotlight, or even a narrow flood of light in a specified space. MR16 halogen lamps, on the other hand, can provide multiple beam spreads and could be considered for a wide variety of applications from task lighting to accent lighting.

Specifying lamps onto a project that can provide the correct beam spread offers designers better control and more precise use of exterior light. Improved control saves energy and protects the surrounding houses or buildings from being washed in uncontrolled and unnecessary light.

The Color

Items look different under different types of light. 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.

When designing exterior lighting systems to highlight textures or materials used in the space, like marble or granite, it will be important to select light sources with higher CRI ratings to protect the integrity of the appearance of the material under the nighttime illumination.

Select Efficient Light Sources: Efficacy + Rated Life

Once the design goals of the space have been identified, it is time to select the most efficient lamp type capable of accomplishing those design objectives.

 

Selecting light sources that are energy efficient and rated to have a long lamp life to minimize energy consumption and material waste. Photo courtesy B-K Lighting

 

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. 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 material lamp waste created throughout the life of the system.

There are a variety of light sources to choose from, but the most efficient matches for the outdoor environment are light emitting diodes (LEDs), compact fluorescent, metal halide and halogen lamps.