Difference between revisions of "Arc Lights"

Revision as of 09:53, 22 July 2016

Arc Lights also known as HID Lights

An arc light is a High Intensity Discharge (HID) light that uses an arc between two electrodes in a gas-filled tube which causes a metallic vapor to produce radiant energy. The electrodes are in close proximity within a sealed gas filled tub and is under pressure. The arc generates extremely high temperatures, causing metallic elements within the gas atmosphere to vaporize and release large amounts of visible radiant energy.

The HID light bulb does not receive direct line voltage like a filament lamp. A ballast is used much the same as with fluorescent lighting. The ballast is specifically designed for the type of arc light bulb being used. HID lamps require a warm-up period to achieve full light output and any interruption disrupts the arc causing another delay to achieve full luminosity.

Mercury Vapor

The mercury arc produces a bluish light that renders colors poorly. Therefore, most mercury vapor lamps have a phosphor coating that alters the color temperature and improves color rendering to some extent. Most street lights once used Mercury vapor bulbs but have since been replaced by low pressure sodium lighting. Mercury vapor lamps provide about 50 lumens per watt, but ballast loss can reduce the system efficacy to about 30 lumens per watt.

There are still a lot of mercury vapor lights in rural America. The are common in the Midwest for the lighting and security on farms. Light service is often provided by the local electric utility company.

Metal Halide

The metal halide light is a more advanced version of the older mercury vapor type. Metal Halide bulbs use chemical compounds known as "halides" that produce light in most regions of the spectrum. The bulb offers both energy efficiency with excellent color rendition. Metal halide lamps are similar in construction and appearance to mercury vapor lamps. The addition of metal halide gases to mercury gas within the lamp results in higher light output, more lumens per watt.

Metal halide lamps have an average life of 15,000-20,000+ hours. They produce 65-115 lumens per watt, more than fluorescent or mercury vapor lamps. The color temperature range is 2700K to 20,000K and CRI (color rendering index) of 65-90. Metal halide generates light closer to sunlight than any other HID light source.

Metal halide is frequently used in indoor settings such as factory lighting, gyms, and other large indoor lighting for large spacious areas. They should not be used for small enclosed areas. Metal halide lights are also used for outdoor security lighting such as parking areas.

High Pressure Sodium

This bulb is designed with a greater focus on energy efficiency rather than color rendition. Mercury and sodium vapors in the ceramic arc tube produce an bright orange tinted light with extremely high LPW performance and longer service life.

High pressure sodium lights are widely used in industrial areas for nighttime outdoor security lighting. These lights are typically in a fixture known as a wall pack or on a pole.

Low Pressure Sodium

This bulb type is even more energy efficient and survives longer than the HPS light, however, color rendition is further sacrificed to a deeper orange colored light.

Most street lighting uses low pressure sodium bulbs. However, with the introduction of new LED technology, as LED bulbs are now becoming bright enough many towns and cities across America are switching from low pressure sodium to LED street lights.