What are the relative lumen efficiencies (lumens/watts consumed)of compact fluorescent, high pressure sodium, and mecury vapor lights compared to incandescent? I understand the CFs are about 4.5 times that of incandescent but it seems to vary.

Also, I have an old outdoor light fixture which has had the same bulb since I bought the house 15 years ago. By the shape of it, it could be a mercury vapor, metal halide, or high pressure sodium based on what I saw at the Big Box Store. How can I tell? The housing is getting surface corrosion and the manufacturer's tag is unreadable.

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Never buy a house built by an oil company...