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	The Trouble With Dimmers:          Household dimmer switches are generally very simple and use devices called SCR's to switch the lights on and off faster than the eye can see. They depend on a stable waveform from the electric company for their operation, but they alter the very waveform upon which they depend! This can result in erratic operation, especially when more than one dimmer switch is installed on the same circuit. In addition, SCR type dimmers can produce excessive heat for their size, audible noise, and electromagnetic interference. These drawbacks are usually offset by the low cost of their design.          However, in low voltage lighting systems the situation is not as good. The dimmer switch must be followed by a low voltage transformer which causes even more erratic operation, more potential to transmit RF interference, and higher cost. The transformer is also massive and bulky.  Advantages of DCdimmers:          Finally, in independently powered applications where a source of low voltage is already present in the ship's battery, it becomes completely impractical to use a household dimmer switch. In such applications, it is far more practical to use a device which is fed directly from the ship's own DC battery and produces a variable low voltage DC output. These devices, called switch-mode power supplies or DC-to-DC converters, are more complicated and expensive, but also more stable, cool running, lightweight, and do not cause interference or audible noise.     Manufacturers exist for relatively inexpensive DC dimmer switches, but these do not insulate against transients in the input battery voltage and cannot protect against premature bulb failure. Negative transients such as the brief dimming caused by starting the engine are likewise passed through.    A proper dimmer switch regulates it’s output against all fluctuations, rather than simply reducing it to some fraction of the input.