Line voltage is the standard voltage that's found in outlets and junction boxes, which is 120 volts in Canada and the United States. Low voltage lighting typically uses 12 volts and rquires a transformer to lower the line voltage from 120 to 12 volts to avoid immediately burning out the low voltage bulb. The transformer for low voltage lighting is either built into the fixture or located elsewhere. The wattage rating of a transformer should be the same or higher than the combined wattage of the lighting system. Transformers typically require a minimum wattage in order to operate the lighting system. The benefits of line voltage include lower-cost fixtures, light bulbs and installation. Dimmers for line voltage lighting are also less expensive than those used with low voltage lighting. Although the initial cost is lower, operating costs are typically higher for line voltage lights unless they're installed in low-use areas, in which case the operating cost difference will be negligible.

While low voltage light fixtures, bulbs and dimmers are considerably more expensive due to the need for a transformer, the operating costs are typically lower than line voltage operation if the lighting system is frequently used. The light produced by low voltage bulbs is warmer, clearer, sharper and looks more natural than high voltage bulbs which produce light that's more diffused. While it's difficult to focus the beam of a high voltage bulb, which tends to scatter light, low voltage bulbs offer a high degree of optical control using just the lamp's reflector. That's because the filament in a low volt lamp is smaller than that in a standard lamp, and most of the lumens are focused in the beam. As a result, less light is diffused. While a low voltage bulb, such as a 50-watt MR16, doesn't use less electricity than a standard bulb with the same wattage, the former will provide nearly 100 watts' worth of illumination for the same power consumption, and light is more effectively concentrated where it's needed, which can reduce the nimber of fixtures needed for a particular lighting scheme.

Low Voltage bulbs last longer, too. A standard household bulb will last around 750 hours, while a standard MR16 lasts 6,000 hours. Low volt lamps also break less frequently than high volt lamps because they're more shock and vibration resistant. Low voltage lighting can be used in the same spaces and for the same purposes as line voltage lighting, but for contemporary lighting schemes, low voltage lighting is ultimately more practical, safer and less expensive to operate. Low voltage lighting is available in a wide range of styles, including recessed can lights, track lighting, rail lighting systems, pendant lighting, display lights and suspended cable lighting. Because more modern lighting options are available with low voltage lighting in terms of fixtures, lenses, bulbs and beams, low voltage lighting is more versatile than line voltage lighting for illuminating artwork, creating a particular ambiance and lighting work spaces. Both line voltage and low voltage lighting systems have advantages, but choosing one over the other largely comes down to the variety of options and the initial operating costs.

Line voltage lighting offers fewer options, but it's less expensive to buy and install, although typically more expensive to operate. Low voltage lighting is available in more options, and while it's more expensive to buy and install, it's typically less expensive to operate over time.There are seven important performance characteristics to consider: lamp life, correlated color temperature (CCT), color rendering index (CRI), lumen maintenance, beam angle and center beam candlepower, lumen output, and luminousCheap Bathroom Mirrors Ebay According to manufacturers' catalogs, the average rated life of MR16 lamps used in architectural lighting applications ranges between 2000 and 10,000 hours. Alberta Health Services Alberta Improvement WayThis lifespan is equivalent to 8 months to 3 years and 4 months, respectively, assuming the lamps are on 8 hours per day. Math T-Shirts Geek

Lowering the supply voltage slightly from its specified operating voltage can extend the life of an MR16 lamp. An MR16 lamp produces light by the incandescence of its tungsten filament. This method of light production, along with the reflector characteristics, determines the lamp’s color characteristics. MR16 lamps have a CCT of between 2800 K and 3200 K depending on the manufacturer and type of lamp. The CCT of MR16 lamps is higher than that of general incandescent lamps because their filament temperature is higher due to a more compact filament size made for low-voltage use. In addition, the dichroic coatings on the reflectors of MR16 lamps remove some long-wavelength light, resulting in higher CCTs. A handful of manufacturers have designed their dichroic reflectors to remove additional long-wavelength light to obtain MR16 lamps with CCTs of up to 4700 K (see “What are MR16 lamps?"). The CRI of MR16 lamps ranges between 95 and 100. The color of the light may change as the lamps age.

The most common reason for this change is the degradation of the reflector coating over time. Degradation occurs because of the decomposition of the dichroic coating or oxidation of the metallic (aluminum) coating materials. All coating materials undergo this process, but some of them withstand decomposition longer than others. The quality of reflector coatings differs from manufacturer to manufacturer and even between products by the same manufacturer. There are two lamp components that determine the lumen maintenance of MR16 lamps: the halogen filament capsule within the lamp and the reflector. The lumen maintenance of the filament capsule is excellent because the regenerative halogen cycle that occurs within the filament capsule keeps the bulb wall from blackening. The halogen gas removes evaporated tungsten from the bulb wall, preventing bulb wall blackening, and in turn, keeping the lumen output relatively constant over time. This process results in higher lumen maintenance than that of non-halogen incandescent lamps.

The lumen maintenance of halogen filament capsules varies depending on the quality of components; at 40% of the rated life, it may be as high as 95% (Rea 2000). The reflector, on the other hand, can affect lumen maintenance negatively over time because of degradation of the coating material or dirt accumulation. Beam angle and center beam candlepower (CBCP) are performance parameters that characterize the beam appearance and the maximum beam intensity of a directional lamp. According to manufacturers' catalogs, the beam angles of MR16 lamps range from 7 to 60 degrees, and their CBCP may range from about 500 up to 15,000 candelas, depending on different wattage and beam angle combinations. Most lamp manufacturers do not publish lumen output ratings for MR16 lamps or other reflectorized lamps in their catalogs. Instead, they publish beam angle and CBCP, which provide more accurate information about the performance characteristics of the lamp. NLPIP tested several 50-watt MR16 samples of the same type (EXN) to determine their lumen output, which ranged between 560 lumens to 710 lumens, and averaged 625 lumens.

In general, low-voltage halogen lamps have higher efficacies than common incandescent lamps because the low-voltage filament is more compact than a 120-volt filament. The low-voltage filament does not need as much electric power to keep it hot. When a low-voltage lamp uses a reflector, its efficacy decreases because of light losses associated with light absorption. NLPIP tested several MR16 samples to determine their efficacy. Efficacies ranged from 12 to 15 lumens per watt. These results account for the light losses from the reflector but not the losses of the transformer, which are 10%, as a rule of thumb. MR16 lamps that use an infrared (IR) coating on their filament capsules have higher efficacies than non IR-coated lamps. The IR coating used in MR16 lamps is a relatively new technology. It is a multi-layer dielectric film used on the outside surface of the filament capsule to reflect the IR radiation from the filament back to re-heat the filament. This reheating causes the luminous efficacy of the tungsten incandescence radiation to increase because less electrical power is required to heat the filament.

Although reflector lamps, in general, may have lower luminous efficacies than non-directional sources such as compact fluorescent lamps (CFLs), their light distribution makes them more effective for directing light in a specific direction without wasting much light elsewhere. Figure 3-1 shows the lighting effects produced on a painting by a 20-watt reflector CFL and a 20-watt MR16 lamp. Figure 3-2 shows how the MR16 lamp provides higher illuminances on the painting compared to the reflector CFL. The light from the MR16 lamp is concentrated within its beam spread with little light spill outside the painting. MR16 lamps have much better optical control and can produce much narrower beam angles while CFLs, although having higher efficacies (lumens per watt), cannot be easily controlled from an optical point of view because the light source is larger. Figure 3-3 shows a plot of the illuminance measurements across the horizontal centerline of the painting for both lamps. As this graph shows, the illuminances measured at the grid points in the painting area are higher for the MR16 lamp than for the reflector CFL of the same wattage.