Metal Halide 101

Proper Use of Metal Halide Lamps

Correct Operation And Cautions For Discharge Lamps

High intensity discharge lamps require auxiliary equipment (ballasts, capacitors, ignitors, and/or power supplies) to provide the correct electrical values for starting and operation. This auxiliary equipment must meet all electrical specifications outlined by ANSI (American National Standards Institute). Venture Lighting International will not be responsible for poor performance, property damage, or personal injury from lamps operating on unauthorized auxiliary equipment, or from lamps being operated in a manner inconsistent with their design.

Power should always be turned off and preferably locked out in accordance with OSHA guidelines whenever installation, removal or maintenance is performed on lighting systems. Always use safety glasses and gloves when installing or removing HID lamps. Replacement lamps should be screwed in firmly, but not with undue pressure, into appropriate lamp sockets. This will avoid loosening due to vibration.

Scratches on the outer envelope, direct contact with water, or excessive pressure can cause these lamps to break. If the outer jacket should break, immediately turn the power off. Do not remove a lamp until it has completely cooled and replace it with a new Venture lamp. Immediately turn the power off if an outer envelope is broken to prevent injury that may be caused by ultraviolet radiation from an unjacketed HID lamp.

HID lamps and their arc tubes operate at extremely high temperatures and may shatter as a result of misapplication, system failure, or other factors. This type of failure may release extremely hot glass and lamp parts into the surrounding environment, causing a risk of fire, personal injury, or property damage. It is imperative for users of HID lamps to use good judgment and common sense for placement of these lamps, in anticipation of potential violent failures. In areas susceptible to contamination by flying glass, where flammable materials are present, or there is a possibility of personnel injury, users should seek additional protective measures. In these cases, the user should install Venture open fixture rated lamps and/or use enclosed fixtures even if the lamp type does not require this type of fixture.

Starting and Restarting Characteristics

When using the proper auxiliary equipment, standard metal halide lamps will start at an ambient temperature of -30 degrees C (-22 F). Full light output does not occur when power is first applied to cold metal halide lamps; there is a time delay of 2 to 4 minutes before lamps reach 90% of their full light output.

Venture’s exclusive Uni-Form formed body arc tube provides faster warm-up and hot re-strike in 60% less time. The external ignitor and the Uni-Form formed body arc tube combine to allow better starting in colder conditions, down to -40C. 

After lamps have started, if there is a power interruption of 1/2 a cycle (1/120th of a second) or more, the lamps may go out and not restart when power is reapplied. It takes several minutes before an arc can be re-established by a standard ballast and/or ignitor. The exact time is dependent on a number of factors including lamp wattage, ballast and/or ignitor characteristics, ambient temperature, fixture dimensions, and supply voltage. As with initial starting, several minutes are required before full light output can be achieved. The time needed to establish full light output can be as short as 5 minutes and as long as 15 - 20 minutes. In general, the use of ignitors and/or special ballasts will dramatically decrease the time for hot restart. See chart on ballast characteristics.

Metal Halide v. Incandescent

Economics

Metal halide is almost always the cost effective solution for general lighting when compared to incandescent lighting technology. Incandescent is often selected for applications where instant light output is required or where only modest light levels or very small bulb sizes are required. Incandescent is also specified because of its low initial cost, since it requires no ballasting and the lamps are less expensive. However, initial cost is not usually a good criteria since the relatively low efficacy of the incandescent system makes it one of the costliest to operate. Metal halide is 3 to 5 times more efficient than incandescent; therefore, the higher initial cost of the metal halide system is quickly repaid relative to the cost of operation for an incandescent system. Although incandescent and metal halide are compact white light sources offering the user substantial versatility in terms of product selection and utilization, the main difference between the two technologies is the efficiency with which they generate light. Metal halide has a substantial efficacy edge over incandescent which often makes it the economic choice.

The Environment

When the choice is between metal halide and incandescent lighting, metal halide is the clear winner for the environment. A 100 watt metal halide lamp provides 5 times the lumen output of a 100 watt incandescent bulb. Added to this is the fact that it will burn for an average of 15,000 hours or approximately 15-20 times the life of the incandescent lamp. In addition to higher operating costs, the incandescent system has greater adverse impact on the environment.

Metal Halide vs. Fluorescent

Metal Halide Advantages

Metal halide lamps are highly compact white light sources. Linear fluorescent lamps, on the other hand, are low brightness sources with relatively large surface areas. This means that metal halide lamps radiate much more light per square centimeter of surface area than do fluorescents. A fluorescent lamp at the highest output has only the total lumen output of a 175 watt metal halide lamp.

Metal halide lamps offer the user a high light level using smaller, very compact fixture designs that deliver high light levels. They lend themselves well to applications where the light needs to be directed or controlled. This ability to direct light produces better light where it is needed and gives rise to more dramatic lighting effects. The inherently higher lumen packages allow the designer to achieve reasonable illumination levels in high ceiling applications.

Fluorescent light sources can be thought of as belonging to two different product families, standard linear fluorescent and compact fluorescent. Standard linear fluorescent does not provide the compact size of metal halide. This source is good for general diffuse lighting, but is hard to direct. Compact fluorescent lamps are small, but their lumen output is somewhat limited.

A major drawback to fluorescent for general lighting is the temperature sensitivity of the lamps with regard to light output. Fluorescent lamps operate well over a relatively narrow range of temperatures and are best for indoor lighting applications where the ambient temperature can be well controlled. The fluorescent lamp is designed to perform optimally at around 70F (21C) and will experience measurable decline in efficacy on either side of this optimum. For this reason, fluorescent lamps use in outdoor applications is much more limited than either incandescent or high intensity discharge sources.

Metal halide lamps, however, are well suited for both indoor and outdoor applications and are relatively unaffected by large changes in ambient temperature.

Metal halide lamps are commonly available today in wattages from 32 up to 2000 watts, with corresponding lumen packages of 2,000 to 210,000. Common fluorescent lamp wattages range from 5 to 215 watts, with corresponding lumen packages of 250 to 15,700. Higher wattage fluorescent lamps are simply too large to be practical.

Metal halide is best suited to those applications that require higher foot-candles and where the lamps are more than 8 - 10 feet from the work surface.

Metal Halide vs. High Pressure Sodium

Metal halide lighting differs from High Pressure Sodium (HPS) in the color and quality of light delivered. Metal halide is a highly efficient light source capable of delivering a white light in the range of 2700 to 5500 Kelvin with typical CRIs in the mid-60s to mid-70s. Some lamp chemistries even obtain CRIs in the 80s. In contrast, high pressure sodium lamps yield yellow lighting (2200K) and have a very poor color rendering index of 22.

HPS lamps are available in color-corrected versions that shorten their life and only slightly improve color temperature. Even with greatly improved CRIs, the color temperature still delivers yellow light. This color limitation is present because the HPS lamp generates light through the excitation of sodium. Metal halide lamps, on the other hand, generate light through the excitation of 2 to 5 different chemicals in the arc tube. In addition, the exclusive Uni-Form formed body arc tube is a newly-designed, compact light source sculpted to follow the physical shape of the arc itself. The precise geometry of this unique arc tube, accurately reproducible from lamp to lamp, produces a metal halide lamp of greater efficiency, improved color uniformity, and longer life.

By varying the blend of chemicals in the arc tube, metal halide engineers are able to alter the characteristics of the light output. This flexibility in design makes metal halide so versatile. White light is a very important attribute of metal halide technology, because it is the closest to the natural sunlight that people prefer.

A number of independent research projects compare each option under low light levels and provide solid, reliable information to support the concept that the color of light strongly influences human perception. In fact, the sensitivity of the eye to different colors determines the true or effective lumen output of a lamp. The visual effectiveness of white metal halide light with a high blue/green content is shown to increase in reduced light while it decreases for the yellow light of sodium sources.

High pressure sodium has been used for years in less color critical applications such as parking lot and roadway lighting. Applications more sensitive to color have used metal halide. The availability of lower wattage metal halide lamps and the revolutionary Uni-Form pulse start system technology has greatly increased its application in indoor and outside commercial and industrial environments. Many applications, such as security and parking garage lighting, now use metal halide instead of HPS. HPS is used today mainly in areas where color temperature and color rendition are less important (i.e. warehouses, street lighting, security lighting). Metal halide is applicable in a wide range of commercial, industrial and municipal spaces and offers an excellent quality of light.

Studies show that people generally prefer to work and live in a white light environment, a fact that itself explains the dramatic shift toward metal halide.