Some light bulbs are better than others for the environment, and in order to find out which ones are better, simply compare them by how much energy they need to produce light. Both halogen and incandescent bulbs produce light by heating a tungsten filament with an electrical current. Compact fluorescent lamps (CFLs), on the other hand, create light through an entirely different mechanism. The fluorescent gas inside the bulb produces ultraviolet light when electrified, and the lamp's coating converts the ultraviolet light into visible light. Because of this, CFLs are between 67 percent and 80 percent more energy-efficient than incandescent bulbs. Halogen lamps stand somewhere in between, ranked as more efficient than normal incandescent bulbs, but not as efficient as fluorescent lights.
Luminous Efficiency
Light is measured in units called "lumens," which correspond to the amount of light produced per watt. For a source of light to be 100 percent efficient, it would hypothetically need to give 680 lumens per watt (see References 1). The luminous efficiency of fluorescent lighting is the highest, between 9 percent and 11 percent for most CFLs, while conventional incandescent bulbs stand between 1.9 percent and 2.6 percent efficiency (see References 1). The luminous efficiency of halogen lamps cradles between the previous two at an approximate 3.5 percent efficiency.
Luminous efficiency is one way to determine which bulb to choose, yielding CFLs as the most efficient, followed by halogen bulbs and then incandescent bulbs. Another element to look at is the watts it takes to produce the same amount of light. For example: It takes an incandescent bulb 60 watts to produce the same amount of light that would take a CFL bulb only 15 watts to produce (see References 2). Manufacturers are required to list both the lumens produced as well as the watts used by every bulb, so luminous efficiency can be calculated easily (see References 5 and 6).
Halogen Bulbs vs. Conventional Incandescent Bulbs
Incandescent bulbs, including halogen bulbs, produce light by heating a filament of tungsten metal until it is white hot. In a normal incandescent bulb, the tungsten slowly vaporizes and deposits on the inside of the bulb until it is too thin to carry an electric current and the bulb burns out. Halogen bulbs are filled with a special gas that causes the vaporized tungsten to be deposited back onto the filament instead of the inside of the bulb (see References 3). Halogen bulbs last longer and also burn hotter than conventional incandescent bulbs, making them slightly more efficient. However, these gains may be negated by the extra energy an air conditioner must use to cool a room.
Effects on Climate
Compared to incandescent bulbs, fluorescent lamps are especially efficient in warm climates. Around 90 percent of the energy used to power an incandescent bulb is transformed into heat, as opposed to 30 percent for CFLs, which use less electricity to begin with. When it's hot out, switching to CFLs not only reduces electricity for lighting, but it also reduces workloads on air conditioners. The opposite is true in cold climates. Without the extra heating from incandescent bulbs, more natural gas or oil needs to be burned to heat homes and businesses. In areas where electricity is cheap or comes from non-fossil fuel sources, switching to CFLs can actually increase overall energy costs and greenhouse gas emissions (see References 4).
New Energy-Efficient Halogen Bulbs
A new class of halogen bulbs has recently been developed. These new bulbs use a special infrared coating to redirect infrared light back toward the tungsten filament, reducing waste heat and improving efficiency by up to 30 percent over typical incandescent bulbs (see References 3). They are still not as efficient as CFLs, which are around 75 percent more efficient than normal bulbs, but this variety offers top-tier efficiency when it comes to halogen bulbs.
References
- Community College of Rhode Island: The Nature of Light
- General Electric: FAQs: Compact Fluorescent
- General Electric: FAQs: Halogen
- Canadian National Research Council: Impact of Conversion to Compact Fluorescent Lighting on Greenhouse Emissions
- General Electric: Halogen Products
- General Electric: Compact Fluorescent Products
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