Why are LEDs superior to HIDs? It's not as simple as comparing energy efficiency, in this case. Instead, there are many other factors, such as lifetime, controllability, and maintenance that make LEDs a more desirable choice for exterior lighting. But first, let's learn how LEDs and HIDs work.
How Do Light Emitting Diodes Work?
LEDs, or light emitting diodes, work by passing an electric current through a semiconductor material. The current excites the electrons in the material, which makes them emit photons, or light. Unlike traditional lighting, LEDs do not contain a filament or gas, which means that they do not emit a great deal of heat. The heat that they do produce is captured by a heat sink that is built into the fixture.
How Do High Intensity Discharge Light Bulbs Work?
An HID lamp is made up of a translucent arc tube, which is filled with xenon gas and metal salts. When the lamp is turned on, an igniter emits a high voltage pulse. The gas ionizes to facilitate the electric arc, which passes between two tungsten electrodes inside the tube. The electric arc evaporates the metal salts, which form a plasma. The plasma increases the light emitted by the arc, which makes it more efficient than many outdoor lighting alternatives.
Comparing LEDs and HIDs
- Energy Efficiency
First, lighting may be labeled at its best possible efficiency, average efficiency over a chosen timeframe, or at its first operational efficiency. With so many possibilities, you cannot directly compare the Lm/W ratings. In the case of HIDs, its initial energy efficiency is much higher than it will be after its been in operation. If operating for full 14 hour nights for 7 days a week, an HID will likely drop to about 80% efficiency in less than two years. LEDs, on the other hand, continue to operate at or near its initial efficiency for much longer. In two years, an LED would operate at 98-100% efficiency. An Lm/W rating doesn't capture this feature of LED lights.
Second, LEDs produce directional light, which means that a fixture can be designed to illuminate a precise space evenly and consistently. HIDs, on the other hand, illuminate the area directly below the HID much more than the surrounding areas. These "hot spots" signify a waste of energy (in addition to increased light pollution and decreased visibility), because the HID must work harder to illuminate those surrounding areas adequately. Plus, a good amount of light is trapped inside the fixture in HIDs. So, an HID illuminating a specific area can be replaced with an LED with a lower Lm/W rating and still illuminate that same area.
- Controllability & Warm-Up Time
- Light Color and Quality
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