LED Street light or Metal Halide Lamp?

Compared with existing lighting technology, solid-state lighting technology using light-emitting diodes or LEDs has two main advantages: lower energy consumption and longer life. In many cases, these two advantages are sufficient to stimulate the conversion from current lighting systems to LED luminaires. Some other features specifically distinguish between LED and metal halide (MH) lighting, and decided to replace the existing technology with new technologies.

1 Choosing LED streetlights or metal halide lamps?

Here are some distinctions between LED street lights and metal halide lamps ,you can have a reference:

a Lifespan and instant-on: LED has longer lifespan and there is no turn-on delay.

MH fixtures produce light by sending electricity through a gas. Usually, gasses will not carry an electric current, so the first step is to ionize the gas within the bulb. That is, the first step is to separate electrons from their home atoms within the bulb. That could theoretically be done very quickly by providing a very rapid burst of high voltage, but that reduces the lifetime of the bulb. So a typical MH bulb will take about ten minutes to get to full operation. In contrast, LEDs emit light immediately in response to current flow, so there is no turn-on delay.

b Different colors: One of the advantages of LED streetlights over other technologies — such as high-pressure sodium and mercury vapor lights — is their “white” light, so white LEDs are often chosen for streetlights.

The mix of mercury vapor and metal halide molecules in an MH bulb emits a fairly uniform white color. There’s a more-or-less standard blend of molecules, so the color you get from one MH bulb is pretty much the same as the color you get from any other. LED streetlights consist of a number of computer-chip-like elements that emit different wavelengths of light, depending upon their specific construction.

There can be subtle differences in the quality of light from LED to LED, but their color is not all that distinct from each other, or from MH lights. In fact, Margaret Newman, the lighting professional leading New York City’s conversion to LED streetlights, says that most people didn’t even notice when Central Park’s MH fixtures were replaced with LEDs.

c Energy efficient or not：MH lamps’ lights are uncontrollable and their structure caused too much loss.

MH bulbs need to be very bright because they don’t distribute their light evenly, so to make sure there’s enough light between poles, they need to start out extra bright. They also waste a fair amount of their light in the fixture, and they are less efficient than LEDs. Putting all those factors together can result in significant energy savings from LEDs. For example, the city of Pittsburgh, California, replaced 1,300 streetlights with LEDs and saved more than 500,000 kilowatt-hours and more than $65,000 in energy costs per year.

d Light pollution: MH bulbs emit light in all directions, while LED can shine toward right the objective.

MH bulbs emit light in all directions, similar to the light distribution from an incandescent bulb. LEDs are designed on the chip package level to send their light in specific directions. Both MH and LED streetlights consist of the source and some optics — mirrors and lenses — that shape the light. Because LEDs offer more control over light distribution, less light is lost in the fixture. If you notice very even illumination between streetlights, you’re probably looking at LEDs. Another LED advantage is that less light is sent up toward the sky, reducing both waste and light pollution.

e Cost and Maintenance: LEDs are more expensive but can save a lot maintenance fee

One area in which MH lamps have an advantage is in initial cost. An MH bulb can cost in the range of $20 to $50 or so, while the least expensive LED fixture will cost you at least $100. But one LED fixture can last as long as 20 or more MH bulbs. When you factor in the cost of maintenance — which can be very high, even when you don’t need to shut down roadways for bulb replacement — an LED replacement program can pay for itself in just a few years.

2 Why are there fewer and fewer metal halide bulbs?

Some metal halide lamps have long warm-up periods (15-20 minutes) when the light is first turned on or in the event that the power source is interrupted. Additionally, there is a small risk that a metal halide lamp can explode. Although this is rare and there are preventive measures that reduce risk, there is still the possibility of injury or damage as a result. Typical preventive measures include changing bulbs prior to their expected end of life and as a group (versus spot changing single bulbs that actually fail). This can significantly increase costs and significantly shorten the useful lifespan of the light.

Additionally, metal halide bulbs are inefficient energy consumers. On top of this, they need to be run for much longer periods of time than actually needed due to the warm-up requirement. This all translates to cost (generally manifested as a higher utility bill). Although they cost about the same as LEDs, metal halide bulbs will keep adding expenses over time based on the inefficient way in which they operate and the frequency with which they must be replaced. In a large-scale building (like a warehouse, hockey rink, or stadium), this inefficiency will really add up.

3 Why LEDs are more popular?

Super Long lifetime: The projected lifetime of LED street lights is usually 10 to 15 years, two to four times the life of currently prevalent HPS. (LEDs themselves do not generally fail or “burn out” in a way comparable to other technologies, and barring catastrophic failure of other mechanical or electronic components of the LED fixture, lifetimes are typically set by a decrease in luminous output of 30%. But the functional lifetime of an LED fixture is limited by the weakest link; associated drive electronics are typically projected to last about 50,000 hrs. It is important to understand that no LED streetlighting products have been in service long enough to confirm the projections.) If realized in practice, the less frequent need to service or replace LEDs will mean lower maintenance cost.

No harm: LEDs don’t contain mercury or lead, and don’t release poisonous gases if damaged.

Less glare: Directing the light downward onto the roadway reduces the amount of light that is directed into driver’s eyes.

Great optics and lens: Other types of street lights use a reflector to capture the light emitted upwards from the lamp. Even under the best of conditions, the reflector absorbs some of the light. Also for fluorescent lamps and other lamps with phosphor coated bulbs, the bulb itself absorbs some of the light directed back down by the reflector. The glass cover, called a refractor, helps project the light down on the street in a desired pattern but some light is wasted by being directed up to the sky (light pollution). LED lamp assemblies (panels) can send light in the desired directions without a reflector.

Low energy consumption: Many LED lighting retrofits have been claimed to dramatically reduce energy use.

Quick turn on and off: Unlike fluorescent and high-intensity discharge (HID) lamps, such as mercury vapor, metal halide, and sodium vapor lamps, which take time to heat up once switched on, LEDs come on with full brightness instantly.

Restart quickly: Unlike mercury vapor, metal halide and sodium vapor lamps (commonly used in street lighting), LEDs do not have a problem restarting immediately (hot ignition) following a brief power failure or inadvertent turn off.

More accurate color rendering: The color rendering index is the ability of a light source to correctly reproduce the colors of the objects in comparison to an ideal light source. Improved color rendering makes it easier for drivers to recognize objects.

LED streetlights are more and more popular and it’s not easy to buy a cost-efficient and right one. There are some factors [click here]you should pay more attention to.