The internals of HID

 Sodium Lights
Sodium lights function in a very similar method to fluorescent, mercury vapor, and metal halide lights. The primary difference between sodium lights and fluorescent lights is the absence of coatings in sodium lights. Fluorescent lights produce light by energizing an inner coating on the bulb through the gas, while sodium lights actually energize the sodium gas trapped inside the bulb to produce the light.
Lighting Process
Sodium lights have an element inside the bulb that allows an electrical current to circulate through the light system. This current is carefully controlled by a ballast that reduces the voltages and current cycles to the proper levels. As this electricity passes through the gas, it gives some of its energy to the sodium atoms. The electrons of the atoms rise in energy levels, and as the current cycle passes they drop back again, releasing their excess energy in the form of light photons.
High Pressure and Low Pressure
The primary physical different between high pressure and low pressure sodium lights is the amount of gas used. Since high pressure gas lights contain more sodium gas, they tend to be brighter and produce a brighter, more golden glow. Low pressure lights take longer to start because they have fewer atoms to react to the electrical current, which in turn needs to build for a longer period before being channeled through the bulb.
Advantages
High pressure sodium lights are very energy efficient, especially compared other high intensity discharge lighting options. This allows users to save money if they plan on having the lights on for long periods of time. High pressure sodium lights have low color rendition index, which limits their application to areas where color in lighting is not important.


MH
No High Intensity Discharge Light has  a filament. Instead light is created from an electrical discharge between two electrodes in a micro-environment of xenon gas and metal halide salts. The light is emitted by an electrically energized gas -- a plasma discharge-- formed and sustained between the two electrodes. The distinctive blue-white light of MH lamps is great for vegitative growth, and reflects better then HPS. Additionally, the increased light output is designed to illuminate a wider area then non-hid. HID lamps have over three times the lumens per watt of traditional halogen light sources and are more efficient at converting electrical energy into light. They produce at least 70% more light than traditional lamps, and use less power while producing less heat. This gives designers new freedom to explore the frontiers of front end design. By creating more compact headlights to fit smaller spaces, better aerodynamics are possible.
Better on the eyes too!


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