At UK we strive to make lights which produce the maximum brightness, with minimum size, and most efficient use of energy. For years technology limited our selection of light sources to incandescent lamps. We found that off-the-shelf lamps were never bright enough and produced light which was often too yellow. The only solution was to work with selected lamp manufacturers to produce custom lamps to meet our specifications which burned whiter and more efficiently.

Incandescent lamp design for flashlights always gets down to three major parameters, color temperature, power, lamp life. These must be adjusted for the needs of the application. Unfortunately they are all linked together. When one is pushed to the limits the others may suffer.

COLOR TEMPERATURE (whiteness):

Color temperature is expressed in degrees on the Kelvin temperature scale (1°K = 1°C - 273). This temperature is close to the temperature of the actual filament in the lamp. As the filament gets hotter the light coming from the filament becomes more white. Near 3400° K the filament melts and the light burns out.

Another phenomenon occurs as the filament gets hotter. The tungsten from which the filament is made begins to evaporate and coat the glass walls of the lamp with a black mirror like coating. This is common with inexpensive lamps. Sometimes the lamp gets so dark that no light escapes and the light seems to have burned out while it actually has not. Evaporation of the filament can be drastically reduced by filling the lamp with argon, krypton or xenon gas. Xenon is the best and is also the most expensive. Evaporation can be further reduced by addition of trace amounts of halogen (bromine or iodine) gas. This also adds to the cost, because special types of glass must be used and special handling is required in the manufacturing process.

Lamp filled with xenon halogen gas mixture

Lamps used in UK lights are designed to operate at the highest color temperature without getting too close to the burnout temperature (3000° - 3200° K.) They are filled with xenon gas to retard filament evaporation and when necessary, some have small amounts of halogen gas added. High performance lamps may cost a little more, but the benefit is a whiter beam of light which makes illuminated objects appear more natural.

POWER (battery life and Haz Loc ratings):

The brightness of a lamp is directly related to how much power (watts) it consumes. Unfortunately in a flashlight there are limitations on the amount of power available. Recharageable batteries can deliver the most power. Non-rechargeable lithium and alkaline batteries supply less power. Lamps which consume more power give off more heat. Too much heat can cause a flashlight reflector or lens to melt. When lights are to be used in "Hazardous Locations" there are restrictions placed on the lamp regarding the temperature of the glass envelope of the lamp. Generally the higher the power or wattage rating of the lamp the hotter the glass becomes. Lamps which must meet UL, CSA, FM or ATEX ratings are designed for lower glass temperature with a consequential reduction in brightness.

Xenon filled lamp permanently mounted in reflector for protection

For all UK light designs, we strive for maximum efficiency in the use of power from the batteries. Lamps give off visible and invisible light. The visible light is what our eyes see when it bounces off of objects. The invisible light is what we can feel when the light shines on our skin. This is called infra-red light and it represents wasted energy. By running a lamp at high color temperature, more energy is drawn into the visible light region and less is released as infra-red light or heat. These lamps produce more light with the same amount of energy than a lower color temperature lamp would produce.

LAMP LIFE (lamp replacement frequency):

Lamp life and high color temperature are mortal enemies. Because the filament in a high color temperature (whiter) lamp runs closer to its melting point it evaporates faster. This causes the lamp to burn out sooner than one which runs at lower color temperature (more yellow).

Other factors affect lamp life. Battery voltage is extremely important. The higher the voltage the shorter the lamp life. For that reason it is important for flashlight owners to use the batteries recommended for a particular light. Fresh batteries tend to have a slightly higher voltage that older batteries. As a result lamps usually burn out when fresh batteries are installed in a light. Rechargeable batteries can shorten the life of a lamp designed for alkaline batteries. The overall voltage of a rechargeable nicad, nickel metal hydride or lithium battery tends to remain higher than an equivalent size alkaline battery and consequently reduces the lamp life slightly.

At UK we do our best to balance the need for high brightness and color temperature against the desire for long lamp life. We do this with strict specifications on lamp design, a careful match of the lamps with batteries and protective mounting of the lamp inside the flashlight.