Halogen Lamps

Answer: Most analog copiers utilize halogen exposure lamps because of their brightness and long potential life. To get the most out of your copiers' halogen lamps and minimize the number of lamp-related unscheduled service calls, you must have a basic understanding of how halogen lamps function and what factors affect their longevity.

A halogen lamp is an incandescent lamp that utilizes heat to generate light and incorporates small amounts of halogen gas to increase brightness and longevity. Most halogen lamps use a heating element (known as a filament) made of tungsten because of this metallic element's very high melting point. However, even tungsten evaporates over time and adheres to the bulb wall, ultimately reducing the amount of light emitted.

When the copy function of a copier is activated, voltage is applied to the halogen exposure lamp's tungsten filament. As the filament heats up, minute tungsten particles evaporate and combine with halogen gas, creating tungsten halide, a gas that does not adhere to the bulb wall under optimum operating conditions. As this gas surrounds the filament, heat separates the tungsten from the halogen and attracts it back to the filament. The halogen gas is released to combine with other tungsten particles, completing a "halogen cycle." This repeating process results in the filament lasting longer and the bulb darkening at a much slower rate than in a standard incandescent lamp, producing increased brightness over a longer life.

LONGEVITY FACTORS

Numerous factors can adversely affect the performance and/or life of a halogen exposure lamp, including electrical voltage variances, surface contamination, and arcing terminal contacts (in some older machines utilizing standard copper contacts).

Voltage -- Halogen lamps are manufactured with a specific amount of halogen gas appropriate to the intended filament temperature. Operation at the specified voltage is critical because it ensures proper exposure of the drum surface and maximum filament longevity. In a halogen lamp operating at a voltage just 10% higher than specified, for example, the temperature will increase, the filament will evaporate more rapidly, the bulb will darken prematurely, and lamp life will be reduced by about 67%. Conversely, if the same lamp is operated at a voltage 10% lower than specified, the decrease in the rate of tungsten evaporation will produce significantly longer life, but this lower voltage will decrease lamp brightness and cause darker copies.

Note: Some lamps that are physically compatible with a given copier may actually have the wrong voltage rating. Again, too much or too little voltage applied to any halogen exposure lamp can result in copy quality problems and/or shorter lamp life. Make sure any lamp you install is specifically designed for the copier being serviced. Equally important, in any copier with a variable exposure voltage control, technicians should always verify and adhere to OEM-recommended optimum ranges when adjusting this voltage.

Contamination -- Contamination of the bulb can also reduce lamp life. Dust, oil from fingerprints, and other contaminants can all greatly reduce the efficiency and life of a halogen lamp. These contaminants often create "hot spots" -- concentrations of heat energy -- on the bulb's surface. A hot spot can cause the tungsten filament to overheat, reducing the life of the filament and, consequently, the lamp itself. In addition, hot spots can lead to an imbalance in the halogen/tungsten mix, with the excess tungsten gas darkening the bulb prematurely. To avoid problems due to contamination, minimize direct contact with the bulb wall; halogen lamps should be wrapped in protective paper or held by the ceramic ends. Also, be sure to thoroughly clean the lamp before installation and during every service call.

Arcing Terminal Contacts -- If a halogen lamp is installed incorrectly, or if the terminal contacts become dirty or corroded, the contact points of the halogen lamp may not mount flush to the contact points in the copier. This can result in electrical arcing and damage to the terminal contacts and lamp. Ultimately this will lead to a break in the electrical circuit, and a service call to replace the lamp and one or both of the terminal contacts.

PREVENTING LAMP-RELATED COPY QUALITY PROBLEMS

Cleaning Mirrors & Lenses -- As mirrors and lenses become dirty and light transmissions are reduced (resulting in dark copies), many service technicians are tempted to compensate by manually increasing exposure lamp voltage. As previously discussed, increasing voltage beyond the specified optimum range will burn out the filament faster and increase tungsten gas -- darkening the bulb and shortening its life. It is far better to routinely clean mirrors and lenses during regularly scheduled maintenance. Most OEMs recommend routinely cleaning lamps, mirrors, and lenses every service call. Proper cleaning -- with the proper materials -- is critical to maintaining optimum performance of lamps, mirrors and lenses. In most cases, lint-free cloth wipes and isopropyl alcohol (or film remover) are the recommended materials for proper cleaning.

Safe Transport -- Document Imaging takes great care to ensure packing/shipping materials for lamps and other fragile components are sufficiently protective. Whenever possible, transport halogen lamps in their original packaging for adequate protection.

ALL HALOGEN LAMPS ARE NOT CREATED EQUAL

The quality of halogen lamps available in the marketplace varies significantly from manufacturer to manufacturer. Component impurity (especially with tungsten filaments) or irregular filament dimensions can result in reduced lamp life and inconsistent copy quality. Leaking bulb seals, caused by cracks or other imperfections, will also reduce lamp life, and inconsistent lamp lengths cause installation problems. Bulbs and other components can be damaged if lamps are not packaged properly.