Metal halides are compounds formed when metal and halogen elements combine. They include things like sodium chloride (salt) and uranium hexafluoride (the fuel used in nuclear energy reactors). Metal halide lamps produce light by passing an electric current through a combination of mercury and metal halide gas. They function very similarly to other gas-discharge lamps (e.g. mercury vapor) - the principal difference being the composition of the gas. The introduction of metal halide vapor generally improves both the efficiency and the quality of the light.
Metal halide lights are 3-5 times as efficient as incandescent bulbs and produce a much higher quality light. In many cases, and depending on the particular mix of metal halides, they have a very high color temperature (up to 5500K). This means that metal halide bulbs can be very useful for high intensity applications like vehicle headlamps, athletic facility illumination, or for photographic lighting. By far the best thing metal halides have going for them is the high quality light they output.
Amongst the deficiencies in metal halide lighting are the following
Metal halide lights have the longest warm-up period of any light on the market. Many metal halide lamps used in warehouses and sports facilities take 15-20 minutes just to reach their normal operating temperature. This is a major issues for several reasons:
They must be operated for longer periods of time than an LED because they do not switch on and off on demand.
You must anticipate when you need light.
Lights might be operated when they don’t have to be (for example during a 30 minute down period) to prevent them from needing the warm-up when turned back on.
Metal halide lights get less efficient when run at less than full operating power. The average bulb lasts around 6,000 to 15,000 operating hours. Depending on the particular bulb, you might spend around the same amount initially with LEDs and metal halides. The problem is that over time you will have to purchase a whole lot of metal halides (2-5) to equal the lifespan of a single LED. Overall that means very high maintenance costs over time.
Among the minor deficiencies in metal halide lighting are the following:
Metal halide lights are omnidirectional. Omnidirectional lights produce light in 360 degrees. This is a large system inefficiency because at least half of the light needs to be reflected and redirected to the desired area being illuminated. The need for reflection and redirection of light means that the output is much less efficient for omnidirectional lights due to losses than it would be for the same light if it were directional by its nature.
Common applications for metal halide lighting includes large sport facilities like stadiums or hockey rinks as well as high bay lighting for warehouses and large indoor spaces.
LED stands for Light Emitting Diode. A diode is an electrical device or component with two electrodes (an anode and a cathode) through which electricity flows - characteristically in only one direction (in through the anode and out through the cathode). Diodes are generally made from semiconductive materials such as silicon or selenium - solid state substances that conduct electricity in some circumstances and not in others (e.g. at certain voltages, current levels, or light intensities). When current passes through the semiconductor material the device emits visible light. It is very much the opposite of a photovoltaic cell (a device that converts visible light into electrical current).
If you’re interested in the technical details of how an LED works you can read more about it here. For a history of LED lighting read here.
There are four major advantages to LED lighting:
LEDs have an extremely long lifespan relative to every other lighting technology (including LPS and fluorescent lights but especially compared to metal halide lights). New LEDs can last 50,000 to 100,000 hours or more. The typical lifespan for a metal halide bulb, by comparison, is 12-30% as long at best (generally between 6,000 and 15,000 hours).
LEDs are extremely energy efficient relative to every other commercially available lighting technology. There are several reasons for this to include the fact they waste very little energy in the form of infrared radiation (heat), and they emit light directionally (over 180 degrees versus 360 degrees which means there are far fewer losses from the need to redirect or reflect light).
Very high light quality.
Very low maintenance costs and hassle.
In addition to the major advantages, LED lights also offer several smaller perks. These include the following:
Accessories: LEDs require far fewer accessory lamp parts.
Color: LEDs can be designed to generate the entire spectrum of visible light colors without having to use the traditional color filters required by traditional lighting solutions.
Directional: LEDs are naturally directional (they emit light for 180 degrees by default).
Size: LEDs can be much smaller than other lights (even incandescent).
Warm-Up: LEDs have faster switching (no warm-up or cool-down period).
For a full list of the many advantages to LEDs read here.
Considering the upside you might think that LED lights are a no-brainer. While this is increasingly becoming the case, there are still a few tradeoffs that need to be made when you choose LED:
In particular, LED lights are relatively expensive. The up-front costs of an LED lighting project are typically greater than most of the alternatives. This is by far the biggest downside that needs to be considered. That said, the price of LEDs are rapidly decreasing and as they continue to be adopted en masse the price will continue to drop. That all said the up-front cost of LEDs when compared to metal halide lights are actually fairly close. Both lights (depending on the specific model and specifications) typically sell for around $10-$30 per luminaire. Of course this can change in both cases depending on the particular light in question.
The first practical use of LEDs was in circuit boards for computers. Since then they have gradually expanded their applications to include traffic lights, lighted signs, and more recently, indoor and outdoor lighting. LED lights are a wonderful solution for gymnasiums, warehouses, schools and commercial buildings. They are also adaptable for large public areas (which require powerful, efficient lights over a large area), road lighting (which offer significant color advantages over low and high pressure sodium lights), and parking lots. For an interesting take on the history of street lighting in the United States read here
What’s The Difference Between Metal Halide and LED Lights:
The two different technologies are entirely different methods of producing light. Metal halide bulbs contain metals that are evaporated into inert gas within the glass casing while LEDs are a solid state semiconductor technology. Both technologies produce a very high quality light. LEDs tend to last much longer and are a more energy efficient and less maintenance intensive technology. Metal halides have long warm-up periods and a shorter lifespan but produce a very high quality light and are one of the most efficient lights when it comes to very cool color temperature outputs.
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 en-masse 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.