- the fixture, such as high bay, shoebox, flood light, wall pack, canopy light, as examples.
- the bulb, that screws into the socket of the fixture
- the ballast, which converts AC electricity to power the bulb
- reflector, which attempts to focus the light energy of the bulb and direct it to where the fixture is aimed
- the fixture mount, the means by which the fixture attaches or hangs.
Metal Halide belongs to a family of bulbs called High Intensity Discharge – or – HID. Other bulbs within the same HID family include Mercury Vapor, High Pressure Sodium and Xenon. What is common across all HID bulbs is they all use a ballast to convert AC to power the bulb.
Metal Halide bulbs are omni-directional. We are all familiar with standard home incandescent bulbs. They are also omni-directional. Light is distributed in all directions. In order to focus Metal Halide bulbs, reflectors are added to the insides of the fixtures to gather and aim light.
Reflectors are highly reflective and have mirror-like finishes. Metal Halide bulbs are initially very bright when new, but fade rather quickly and require long strike (start-up) times to produce their maximum producible light levels. If the fixture is turned off, the bulb must first cool down before the long strike time starts up again.
The two most common HID bulbs in the family are metal halide and high pressure sodium. It is easy to distinguish the bulbs apart. High Pressure Sodium bulbs create an orange light. Metal halide light is much whiter.
Applications for Metal Halide Fixtures
Outdoor applications include parking lots, stadiums, street lights and area lights. Metal Halide bulbs come in a variety of wattages for different applications.
Large fixtures with high wattage bulbs use 1000 Watt, 1500 Watt and 2000 Watt Metal Halide bulbs.
Smaller bulbs used in bay fixtures and parking lit lights use 250 Watt and 400 Watt bulbs.
Smaller wall mounted fixtures with less lighting requirements, 100 Watt and 150 Watt bulbs.
Life of a Metal Halide bulb
Metal Halide bulbs have different lifespans, between 12,00 hours to 20,000 hours. During this lifespan, light out degrades with the age of the bulb. It is not uncommon that after 1/2 life of the bulb, the Metal Halide bulb has lost over 50% of its effective lumens.
A bulb that has used 80% of its life is only producing 20% of its initial lumens. Thus, it is not uncommon to replace bulbs well before complete End of Life.
A phenomenon associated with Metal Halide lamp wear and aging is discoloration of the light. In Metal Halide bulbs, this means the shift is to a blue or violet shade.
Converting Metal Halide Fixtures over to LED
So why are users of Metal Halide Fixtures converting to LED? When LED was in its infancy 11 years ago, LED barely produced enough light to replace Metal Halide bulbs. LED was inefficient, and expensive.
LEDs have matured, and mass production has brought down the cost of the product. LED options now produce enough lumens to compete against their Metal Halide counterparts. LED offer several advantages over the Metal Halide fixtures.
LED is energy efficient, using 25% of the energy that a Metal Halide bulb uses to produce the same amount of lumens.
LED’s life spans are much longer than Metal Halide. A 20,000 hour Metal Halide bulb reaches half-life at only 10,000 hours and has already lost 1/2 of its initial lumens. Some LEDs currently have a L70 (70% of initial lumens) of 200,000 hours.
The quality of LED light is better than Metal Halide lighting. Some metal halide bulbs have a high Color Rendering Index (CRI), but most LED products have a high CRI. High Pressure Sodium have a horrible CRI.