China manufacturer of magnetic ballasts for metal halide flood lights & hps flood lights

High pressure sodium lighting may be more efficient and needs to be replaced less often.  People who are concerned about the environment may choose either type of lighting. However, HPS lamps tend to last longer. This means more convenience for you because of less frequent replacement. It also means better news for the earth since it takes longer for these lamps to end up in landfills.

HPS is sometimes preferred for outdoor lighting.  The reason for this is that night vision tends to be affected more by the metal halide lighting than by the HPS lighting.  If you have a group of people outside under lighting who also need to see things that are going on outside of the lit area then you might want HPS lighting.

HPS provides better quality lighting at a lower cost and with less damage to the environment.
Metal halide is much less efficient than high pressure sodium--MH produces much less light per
watt; MH produces more glare due to the blue light component and increases adaptation time;
MH more effectively shuts off melatonin production which can trigger tumor growth; MH
contains more mercury within the bulbs; MH bulbs need to be changed more frequently; and MH
costs more, overall.

Metal halide lighting differs from High Pressure Sodium (HPS) in the color and quality of light delivered. Metal halide is a highly efficient light source capable of delivering a white light in the range of 2700 to 5500 Kelvin with typical CRIs in the mid-60s to mid-70s. Some lamp chemistries even obtain CRIs in the 80s. In contrast, high pressure sodium lamps yield yellow lighting (2200K) and have a very poor color rendering index of 22.

High pressure sodium lighting has lower levels of mercury.  People who are concerned about the potentially toxic effects may want to choose HPS lighting for this reason.  MH lighting is still safe but this is a big issue for some buyers.