Re: Most effecient lighting?????????
Metal Halide is being replaced with T-5/electronic flouresent lighting. It is more energy efficient, can be switched for daylight controls, and has instant on, the lamp life is far longer, and lamp color does not change over life as with Metal Halide.
Low Pressure Sodium is more efficent than HPS, but has very poor color rendition, and the lamps are very long
For outdoor area lighting, the source of interest is the induction lamp. a radio frequency generator excites the lamp, estimates are 100,000 hrs + lamp life (HPS is 24,000). There is a large project in Arizona with 7,000 inductions street lights being installed. Induction ligting has a good color rendition, similar to HID, but is instant on. HID lamp life is about 12,000 hrs.
Of course LED applications are not too far off.
For the average inside application, the best source is T-8 with electronic ballast. Also the compact flouresents are a good source for a downlight.
For the typical outside application, HPS is the standard, however, there are now fixtures with 42 and 84 watt compact flouresnet, but keep in mind compact flouresent (I think I have mis-spelled it) has a short lamp life of 12,000 hours.