Posted by Kolmart.com on 11/7/2010
They both require a matching HID ballast to operate.
Both metal halide and high pressure sodium ballasts and lamps have a standard ANSI code that make them easy to match up, a 400 watt metal halide ballast has an M59 ANSI code, so, you would run an M59 400 watt metal halide lamp with an M59 400 watt metal halide ballast for example. This is true for metal halide, mercury vapor and high pressure sodium.
The main noticeable difference between metal halide and high pressure sodium is the color of the light output. Metal Halide color temperature is normally above 4100K, which is in the spectrum of the white color temperature hues, whereas high pressure sodium is usually around 2100K-2700K which is an amber or golden hue and towards the red color hues.
Light output is measured in lumens which is a measure of the amount of light being emitted from the lamp. High pressure sodium actually has more lumen output than an equivalent metal halide does. For example the 400 watt high pressure sodium lamp puts out 51,000 lumens and the same 400 watt metal halide lamp puts out 36,000 lumens of light.
High pressure sodium wins again as the high pressure sodium lamps have a longer life span than the metal halide lamps do. For example, a 400 watt metal halide lamps rated lifespan is 10,000 to 15,000 hours where the 400 watt high pressure sodium lamps have a standard life of 20,000 hours. Also, high pressure sodium is available with dual arc tubes, meaning there are 2 filaments in the bulb and those are rated at 40,000 hours.
Preference for Lighting Applications:
The question to ask is if you want a white light or an amber colored light. White metal halide light works well for certain applications and some applications are better with sodium. For example, lighting a large parking lot might work better with sodium, because light quality is not as important as the amount of light being available for a certain amount of wattage consumption. Also, sodium light cuts through fog and mist better that metal halide light. On the other hand, if you have a used car lot for example, and light quality is important, then metal halides white light would be a better choice.