.Lamps 

Lamps or light bulbs produce the light and therefore are the most important components in the system. Lamps determine the amount of light, the quality of the light, and the spread of the light.

By far the most common type of lamp used in low voltage landscape applications is incandescent. Incandescent lamps produce light when electricity passes through a tungsten filament. The electrical resistance of the filament causes the electrical energy to be converted into heat energy and light. To increase its life, the filament was originally in a vacuum inside a glass bulb. Today’s modern bulbs use the gas Argon instead of a vacuum. The bulb may also be filled with other gases or coated to alter the color, life, or other characteristics of the lamp. Halogen is a gas that is commonly used in lamps for landscaping projects. This gas extends the life of the filament, amount of light produced, and it produces a whiter light.

There are several characteristics that must be considered when selecting the best lamp for a particular application:

Wattage
Low voltage lamps can range in wattage from a fraction of a watt to more than 200 watts, however most landscape lighting is done with 4 watt to 50 watt lamps. Wattage is a measure of power consumption. Generally, the higher the wattage the higher the light output, but other factors may influence the efficiency and light output as well.

Candle Power
Lamp output or intensity is measured in candelas. This unit of measurement originated using the light output of a common candle as the standard. The number of footcandles of light falling on a surface can be determined by dividing the lamp’s candle power by the distance the surface is from the lamp squared (CP/D² = FC). 

Reflector Type
Lamps designed to direct the light in a specific shape or direction have a defined shape and reflective material inside the lamp. PAR lamps have a parabolic aluminized reflector built into the lamp. MR is the acronym for mirrored reflector, which uses a pattern of small mirrors that work together to direct the light.

Base
The base of the lamp determines how the lamp is attached to the fixture and how it is energized. Common bases are screw terminals, 2 pin (which are pushed into the socket), bayonet (push and twist into the socket), wedge (push in), double ended (snap into socket), bi-pin (push into socket). Bases used for outdoor lighting should be made of brass or nickel-brass. Generally all PAR lamps will be screw terminal, MR halogen will be 2 pin, and bare bulb lamps will be bayonet.

Beam Spread
On reflector type lamps (PAR and MR) the light leaves the fixture as a cone of light. The angle formed by the outside edges of the cone determines the spread of light. Beams of 25 degrees or more are considered flood lights and those of less than 25 degrees are called spot lights. Photometric charts, which are available for all lamps, list the beam angles and luminance in foot candles at various distances from the lamp. Bare bulbs have 360 degree beam spread. This information is critical when designing a lighting system.

Size
Obviously another factor that affects fixture design and selection is the size of the lamp. Lamps are measured in 1/8^th inches. For example, an MR16 is 16 one eighths inches or 2” in diameter (16 x 1/8” = 16/8” = 2”). A PAR 36 is 36 one eighths inches or 4 ½” in diameter. “T” type lamps are measured the same way, so a T3 is a 3/8” tubular lamp, a T5 is a 5/8” tubular lamp and so on.

Color Temperature
The light produced by a lamp can vary in the “whiteness" of incandescent light. Color temperature is directly related to the physical temperature of the filament in incandescent lamps so the Kelvin (K) temperature scale is used to describe color temperature. A higher temperature color (K) describes a visually cooler, bluer light source. Typical color temperatures for lamps used in landscaping are 2800K (incandescent) and 3000K (halogen). They are much “warmer” colors than the cooler and bluer fluorescent lamps.

Lamp Life
All lamps will fail eventually. If not damaged, the filament will be destroyed in time. One of the benefits of halogen type lamps is that the halogen causes the particles of filament to be re-deposited back onto the filament, significantly increasing its useful life.

The average life of a lamp is determined by lighting 100 lamps and counting the hours until 50 have burned out. For lamps typically used in landscaping, lamp life can vary from 500 hours to 30,000 hours with most falling in the range of 1000 to 5000 hours. Lamp life is significant not only from an economic perspective, but also because of convenience. For a light located at the top of a large tree, it is obviously better to have a 10,000 hour lamp rather than a 500 hour type.

Voltage
Lamp life, light output, and color temperature are affected by voltage. The specified values for a given lamp are based on a voltage at the lamp of 12 volts (11.8 volts for some models). Operating the lamp at any other voltage will change those values. The table illustrates the effects on life, output, and color temperature for various voltages:

As can be seen from the chart, small changes in the voltage can have a big impact on the performance of the bulb. Voltage can be controlled at the transformer when it is equipped with multi-taps and it can be affected by the length and size of wire that is used to deliver the power to the lamp. The impact of voltage on lamp performance will be discussed in the sections on wiring and design as well as.