Halogen lamps are a type of incandescent light bulb, utilizing a small amount of special gas added inside a high temperature resistant quartz envelope. This gas comes from a group of elements called halogens, which include iodine, bromine, chlorine, and fluorine. They were first invented by two engineers at General Electric and were originally called quartz-iodine lamps.
Like standard incandescent bulbs, halogen lamps produce light using a thin filament wire that heats up until it glows. This filament is made of tungsten because it can handle very high temperatures. Over time, though, tungsten slowly evaporates from the wire and blackens the inside of the bulb. When that happens, the bulb gets dimmer.
Halogen gas helps the evaporated tungsten to return to the filament instead of sticking to the quartz. This is called the halogen cycle. Because of the halogen cycle, the bulb stays brighter longer and lasts longer before expiring.
The halogen cycle technically explained:
As tungsten begins to evaporate from the filament it combines with halogen gas and becomes a tungsten halide. This tungsten halide state is maintained at temperatures between 250 and 1400°C. The temperature of the bulb must be kept above 250° C in order to prevent evaporated tungsten from clinging to the quartz wall and darkening it. When the tungsten halide nears the filament, the heat of the filament separates the tungsten from the halogen gas, redepositing the tungsten to the filament. The separated halogen gas then repeats the cycle. The halogen cycle greatly increases the life and brightness of the lamps.
• The halogen cycle greatly increases the life and brightness of tungsten filament lamps.
• The halogen cycle prevents darkening of the quartz bulb for consistent light output and color temperature.
• The halogen cycle increases correlated color temperature from approximately 2700K to 3000K.
Parts of the Halogen Bulb
Quartz is used for the bulb/tube/capsule material because of its high temperature requirements to maintain the halogen cycle. Transparent quartz is most used for common halogen bulbs and frosted transparent quartz is used to diffuse and spread the light more evenly. Translucent quartz is favored in some infrared heating applications. More durable lithium aluminosilicate can be used for critical applications. Quartz is a permeable material so oils can be absorbed from bare hands causing damage to the bulb wall. We source our quartz for purity and consistency. We collaborate closely with our customers to design optimal filaments, recognizing that they are a critical component of lamp performance. We specialize in engineering double-coiled filaments to ensure maximum efficiency and world-class quality.
Halogen Gas such as Iodine, Bromine, and Chorine are combined in very tiny amounts with inert gases like Nitrogen, Argon, Krypton or Xenon. The halogen gas creates the halogen cycle to reduce tungsten evaporation and controls heat transfer. This results in a brighter and whiter light, longer life, and clearer quartz over the life of the bulb. For long life applications, gas fill pressure may be at one to three atmospheres. Because of this, all halogen lamps must be used in fully enclosed fixtures with safety glass.
Too much halogen gas can corrode the filament and disrupt the halogen cycle. Too little halogen and the tungsten filament may erode faster. Our formulas of halogen mixtures have been perfected through decades of experience to provide lamp life consistency. At KLS, a wide range of wattages from 5W to 6,000W are available. We carefully determine and fill a suitable ratio of gases for each lamp type. Gas mixing is done in-house, making it possible to support optimum gas concentration and consistent quality.
Tungsten (wolfram) has been used as a lighting filament since the time of Thomas Edison. Tungsten can be malleable, but has an extremely high melting point at 3,422⁰C / 6192⁰ / 3695⁰K. Our filaments are manufactured to a high uniformity standard to prevent sagging and aiding in longer life cycles. If the filament is not uniform, hot spots are created along the filament causing greater evaporation and thins spots, resulting in shorter lamp life. KLS’s tungsten is certified to be sourced from non-conflict mineral zones and smelters.
Filaments
Filaments are formed in different shapes to match the optical requirements of the intended application and optical system. There are many different filament types available, and each are carefully matched to the envelope size and gas pressure. Custom filament and structures can be built to suit specialized applications.
C = Coiled (Single Loop)
CC = Coiled-Coiled (Double Loop)
CF = Flat Coil
D = Double support structure
Filament Alignment
To precisely control the light output, KLS provides lamps with filament and dimension accuracy higher than that of generic lamps. Our alignment accuracy should satisfy customers with critical optical requirements such as in the medical, machine vision, and airfield/aircraft industries.
Molybdenum foil is used in the pinch seal area of the quartz bulb to conduct current from the filament through the seal to the outer pins and base of the halogen lamp. Molybdenum has nearly the same rate of expansion as quartz and thus is the best matching material for hermetic sealing of the bulb. The pinch seal of the lamp is a critical process to produce a durable product.
Reflectors & Reflector Coatings
KLS’s MR11, MR13 and MR16 glass reflectors are sourced from only Tier1 glass manufacturing and glass coating companies. Most visible light transmission applications require Infrared (IR) above 700nm to be filtered to reduce infrared heat to the light plane. Dichroic coatings allow more visible light to pass through the front of the reflector while passing the infrared heat to the back of the reflector. KLS’s light quality is achieved through uniform dichroic coatings to give consistent light output over the life of the lamp and reduced color shift. Dichroic reflectors are typically used in fiber optic illumination, blood analysis, microscopy, and machine vision where visible light is needed and IR is reduced.
KLS utilizes aluminum vapor deposition coatings applied for lamps used in specialty applications where wavelengths above 700nm in the infrared and near infrared spectrum is critical. Machine vision and infrared heating are the most common applications for the aluminized reflectors from KLS.
Gold coated reflectors are also available from KLS on a custom order basis. Applications for the gold reflectors include the most critical NIR/IR reflection. Infrared heating, IR gas detection are a couple of applications for gold reflectors.
Reflector Surface Types
Faceted – Multiple faceted reflectors used to collimate light into a defined, focused beam pattern for directional output.
Stippled – Rough surface scatters light for more diffuse, uniform and soft light.
Specular – Smooth surface like a mirror. All rays are reflected and coherent provided a clear concentrated beam of light.
Lamp Base & Lead Wires
KLS lamp bases are typically made of steatite ceramic or nickel-plated metals. KLS lamp bases are made to exacting ANSI and JIS standards to ensure fit form and function for your lighting application. A variety of standard lamp bases are available, or a custom base designed for your OEM applications can be built. Standard lead wires of stranded nickel, or insulated materials are available. Custom lead wires and terminal ends can also be applied to your specification.
Halogen Lamp Life
Average life is calculated by 50% of the lamp failing before average life rating and 50% before the average life rating.
Voltage Variation – As a general rule, if 90% of the rated voltage is supplied (under-voltage), the lamp life will be extended by 3.5 times. If 110% of the rated voltage is supplied (over-voltage), the life will be shortened by a third.
Halogen lamps are made with a specifically measured amount of halogen gas appropriate to the specific filament temperature and capsule volume. If the lamp is operated at a lower voltage which does not raise the temperature to engage the halogen cycle, the excess halogen gas will erode the filament and shorten lamp life. In contrast, if the lamp is operated at a higher voltage than specified, the bulb wall will darken from excess tungsten evaporation.
The operating voltage of a lamp should be of high consideration when using halogen lamps. If the lamp is dimmed for prolonged periods of time, the lamp should be operated occasionally at the rated voltage to engage the halogen cycle properly.
“Dirty Power” with high voltage spikes and excess vibration will have a significant negative impact on halogen lamp life. Ensure that regulated voltage is applied to the lamp and avoid vibration from neighboring equipment to prolong the life of a halogen lamp.
Excess ambient operating temperature will also have a negative impact on lamp life. Proper ventilation and forced air cooling should be applied accordingly to keep the seal temperature of the lamp within specification. Seal temperatures above 350⁰C will cause oxidation of the molybdenum foil breaking the seal and may result in shattering of the quartz. KLS can provide handmade lamps with a thermocouple attached to the seal for testing and experimentation for an engineering fee.
Bulb wall temperature needs to be at 250⁰for the halogen cycle to operate. The maximum bulb wall temperature is approximately 550⁰C for standard halogen lamps.
DC vs AC power – Halogen lamps can operate on both AC and DC power depending upon their design. DC transformer operation and performance as well as AC voltage fluctuation can have a significant impact on lamp life. Considerations of voltage drop on long runs will also impact light output and lamp life.