The Math on Low Voltage Lighting Systems
The maximum feed in most households is 120V at 20 amps. If you consider the equation: P (power or Watt) = V (volt) X A (amp), you can work out the maximum size of your fixture per circuit. So if you had a circuit with 120V at 20 amps, your maximum allowable fixture on that circuit would be 2400 Watts. Of course you wouldn't have one fixture burning that much power, but you get the idea.
The problem with line voltage lighting is that, when considering electricity used versus lumen output, it is fairly power hungry – not a very efficient choice. Low voltage lighting systems correct this issue by lowering draw and increasing lumen performance. For instance, if you were to have a 50W low voltage fixture, it would produce the same lumens as a 125W line voltage incandescent.
In this age of energy conservation, the low voltage systems are providing a lighting option that will help protect our future. Low voltage lights also have another environmentally friendly element. With a lamp life of approximately 4000 hours, each bulb will last considerably longer than their regular incandescent counterparts. The minute voltage draw is safer for the user because it produces a much less violent shock... if you are not careful and get shocked that is :-)
Classically, inductive systems that require ballasts, such as fluorescent lighting does, have been the mainstay of low voltage systems. Now with new technologies, halogen lights are becoming more and more prevalent. These types of fixtures require transformers to reduce the amount of voltage running to the lights from 120V to 12V.
Transformers can be wired or electronic. Wired transformers are usually heavier and larger than the electronic versions. While electronic transformers are easier to deal with in regards to weight and space required, they are limited to 80” runs because of their high frequency output; therefore, they max out with a total of 105W worth of power.
This means they would be better utilized for small light groupings or single fixtures. Wired transformers run at 60 Hz and have the capability to run more than 80", giving you the ability to have a total of 300W of power without EMV problems. Therefore these would be perfect compliments for track lighting with higher power requirements.
Because of their low voltage nature, all low voltage lamps can be dimmed to zero without drop off. However, not all electronic transformers and for that matter, inductive ballasts in fluorescent lighting, have this ability; if they do, they require specialized inline dimming mechanisms. Not all manufacturers provide these dimmers with their products, so you will have to check for compatibility before you make your LV system purchase.
For more information using low voltage lighting, please read the following articles: