The two branches of the lamp family tree could be drawn as follows. If you look closely you will see that there is a group called High Intensity Discharge within the electric discharge branch. These are lamps which are very similar in shape and size and are used in the same types of applications.
+----------------------------+
| Lamps using incandescence |
+----------------------------+
/ \
Incandescent Halogen
+--------------------------------+
| Lamps using electric discharge |
+--------------------------------+
/ / | \
/ / | \
-------- / | \
/ / | \
Compact fluorescent | | Low Pressure Sodium
| |
Fluorescent |
|
+--------------------------+
| High Intensity Discharge |
+--------------------------+
/ / \
--------- / \
/ / \
Mercury Vapor Metal Halide High Pressure Sodium
Another way to group the lamp types is by shape and size. Lighting designers think in terms of how the light from a luminaire can be used. Point sources can be directed more easily and either concentrated into a beam or spread out from a single source such as a lamp post. Distributed sources are best used to provide even illumination.
Incandescence Electric Discharge Point Sources Incandescent Compact Fluorescent Halogen Mercury Vapor Metal Halide High Pressure Sodium Distributed Fluorescent Sources Low Pressure Sodium
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