The world of lighting systems serves a wide variety of situations and categories. A typical installation will include many lamp types including HID, low and high pressure sodium, mercury vapor, metal halide, halogen, and fluorescent lamps. There are many lighting vendors, but only a few specialize in efficient lamping. As a primer to lamping terminology:
Light output is measured in lumens. A light source has both a color temperature, those color tones which the light amplifies (cool, warm, etc.) and a color rendering index (CRI) or the ability to display color properly in a given color temperature (compared to a full spectrum light source).
The primary lamp manufactures produce hundreds of bulbs, ballasts, CRI, and color temperature items. It’s best to see a lighting distributor to find the widest selection of fixtures and lamping. Sometimes homecenters will have a fair selection, but those are usually the high volume inexpensive lamps, and not the best selection or variety.
A description of each lamp includes:
HID (High Intensity Discharge ) Lamps
A general category of lighting technology is the electrical excitation of a gas to where high energy visible light is radiated. Because the gases report at very well understood spectra or visible wavelengths, electrical energy is not lost heating the air, but converted to visible light at extremely efficient lumen to watt ratios. HID light sources are the most energy efficient commercial light sources available, beyond compact fluorescent, halogen, or incandescent.
Low Pressure Sodium (LPS)
The familiar pumpkin orange light prevalent in parking lots and municipal streets is the most energy efficient light source. Unfortunately with the amber light all colors also appear orange, with little differentiation other than blacks, grays, and orange. Here is where CRI is critical. An experience is trying to find ones vehicle in a crowded parking lot, with all the cars looking the same shade and haze. LPS is a good choice for non-crucial lighting, but generally not applicable to the home.
High Pressure Sodium (HPS)
A variation of bulb pressure creates a different quality of light, yet the prevalent tone of the light is amber, with CRI increases to 40-60 (based on a zero to 100 scale). Using optical coatings a color corrected HPS lamp can be made, but this robs the lamp of it’s inherent energy efficiency.
Older generation lamps used mercury under pressure, similar to sodium, which created a white light source. Today Mercury Vapor lamping is very inefficient compared to HPS or metal halide technology.
Metal Halide (MH)
A new family of lamps is made by varying the gases inside the discharge bulb. MH lamps have very good CRI (75 to 85) and are the standard choice for demanding lighting applications such as athletic fields, indoor arenas, landscape lighting, and recently, using low wattage varieties, a replacement for halogen lights and a ideal source for remote source applications.
Halogen & Incandescent Lamps
In the category of incandescent lighting technology the primary light emitting source is from the heating of a thin strip of metal, namely tungsten. If enough wattage is pushed through the filament, the wire will begin to glow from a dull red, to orange, finally ending up a bright white point source. The inefficiencies are numerous, namely most of the energy is used to maintain the metal hot, leading to many household fires and burns.
A new type of halogen bulb uses an infrared reflective coating, distributing the heat producing wavelengths back to the surface tungsten filament, making the bulb more efficient, but still many times less than a standard fluorescent lamp.
Fluorescent lamps have fallen victim to poor marketing and confusion. Many people’s experience is the inexpensive cool white four foot lamps with hum and flicker of the light. Colors look bad, and some people got headaches from the fluorescent source. As with many of the above lamping choices, two elements make up the light fixture, or luminaire, the lamps and ballast. A ballast is the electrical device that controls starting and maintaining voltages to the lamps.
Using electronic ballasts with high CRI fluorescent lamps, the lighting experience is by far the finest. Fluorescents come in compact and tube types with multiple color temperatures (warm, neutral, cool) and CRI from 60 to 95 rating. The electronic ballast eliminates flicker and hum, a shortcoming of old technology (magnetic ballast).
Light-Emitting Diode (LED) Lamps
The new poster child for high efficiency lighting goes to modern LED lamps with record lumens to watt output. There lifetime is superior to fluorescent lamps and light output is constant. It just might be the last light bulb you buy in a lifetime!