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Why xenon burns brighter and LED lasts longer

June 2006
Whether its a lantern to illuminate a campsite, a focused beam to bait a hook, a torch to show the way on a hiking trail or a light at the end of the tunnel when diving, there are a myriad lighting options practically tailor-made for every outdoor activity. Some burn long, some burn sharp, some burn hot, some burn cold and some just burn once

Some, like the ordinary vacuum-filled incandescent bulb do not burn very efficiently: it has a short life span, dims as the atoms escaping from the tungsten filament form a dark blob on the bulb wall and wastes energy as only 10% of the light produced is within the visible light spectrum.

Filled with cheaper inert gases like nitrogen or argon with atoms that are big enough to bounce the tungsten atom back to the filament when they collide, it becomes slightly more efficient.

But, unfortunately, these gases also convey heat away from the filament, and as they become hot and rise to the top, they again deposit the atoms on the bulb wall. The bulb burns out when too much tungsten evaporates from the filament, so that electricity current can no longer be conducted efficiently across the filament.

Fill the bulb with a premium inert gas like krypton or xenon (even better!) and their seriously big atoms will allow even fewer of the escaping tungsten atoms to pass and they speedily send them back to the filament.

Pros: Premium gas-filled bulbs will conduct less heat away from the filament than ordinary gas, so that it can burn hotter and longer ... a xenon bulb can therefore draw from .35 to 10 amperes as opposed to the roughly .5 amp drawn by the standard gas bulb. They will burn twice as long as the standard gas bulb.

A xenon bulb also has about 15% more candle power per watt than a krypton lamp and the light colour is very close to daylight (6000° Kelvin).

Cons: Krypton is slightly more and xenon considerably more expensive than the cheaper gas-filled bulb. They do not "catch" all the tungsten atoms and some do escape to form a dark film on the bulb wall. The tungsten therefore develops weak spots that do break at some stage.

Add halogen to the gas fill and you’ve got an even brighter light that shines even longer. A halogen "capsule" or bulb is normally filled with over 99% inert gas (cheaper argon, better krypton or top end xenon) and less than 1% halogen vapour.

A halogen bulb uses a chemical trick to prolong the life of its filament ... the halogen combines with the tungsten filaments that have condensed on the inside of the bulb and carries them back to the filament. When they touch the hot filament, the tungsten atoms are redeposited there, and the gas is released to do the same trick again.

Because the bulb wall is cleaner, a bright light shines through, even as the bulb ages.

In order for the halogen cycle to work, the bulb surface must be very hot, generally over 250° Celsius, because the halogen may not adequately react with condensed tungsten if the bulb is too cool. This means that the bulb must be small and made of either quartz or a high-strength, heat-resistant grade of glass known as "hard glass".

Costs rise when moving to a harder glass, so typically the glass envelope is made much smaller, but this means that it gets hotter. Since the bulb is small and usually fairly strong, the bulb can be filled with gas to a higher pressure than usual, making it economical to use.

Pros: Halogen provides a very bright light that can be focused well on a specific spot. The hotter filament of a halogen bulb emits relatively more blue or white light, and relatively less infrared light than a regular bulb, giving it a whiter appearance and making it more energy efficient than a regular bulb — it lasts 2 to 3 times longer than a regular bulb and is often 10 – 20% more efficient.

Halogen lamps are ideal where a relatively small, bright lamp and high wattage are required. They are good for providing tightly focused bright pools of light, rather than general illumination over a larger area.

Cons: Halogen draws a lot of power and therefore drain batteries fast. Although the halogen cycle lasts longer than the incandescent light bulb, it has a limited lifespan because the halogen gases cannot place the tungsten on a specific spot on the filament. Therefore, weak spots with too little tungsten covering will develop and the filament will eventually break.

It is more expensive than incandescents and because it burns hot the risk of fire is higher than with cold burning fluorescent and LED lights.

Fluorescent lamps, used in battery-operated camping lanterns, burn much cooler than incandescent lamps, because they convert 3 – 4 times more energy into visible light, and far less into heat. Like other gas-filled bulbs, they also work through electrons and atoms bumping against each other.

The bulb is filled with low pressure argon or krypton gas and mercury vapour and the inner surface of the bulb is coated with a fluorescent paint made of varying blends of metallic and phosphor salts. The coiled tungsten cathode releases electrons at relatively low temperatures, which collide with the gas atoms. They are rapid conductors of heat, which causes the mercury to emit ultraviolet light. This is absorbed by the bulb’s fluorescent coating, which radiates the energy back at longer wavelengths as visible light. The phosphor coating on the bulb controls the colour of the light, and prevents the harmful UV light from escaping.

Blacklights are a subset of fluorescent lamps that provide long-wave ultraviolet light, rather than visible light, that are used to attract insects to bug zappers.

Pros: Fluorescent lamps are much more energy efficient than incandescent light bulbs because they convert three to four times more of the consumed energy to usable light, and less energy into heat. With the result that a fluorescent lamp usually lasts between 10 – 20 times longer than an incandescent lamp. Although a fluorescent bulb will initially cost more, this is offset by lower energy consumption over its life.

Cons: The light transmitted by lower end fluorescent lamps are often harsh and unnatural, colouring skin tones blue. This is because the phosphor used mainly emits yellow and blue light, and relatively little green and red. The triphosphor mixture now used in better quality lamps distribute the emission bands more evenly over the spectrum of visible light and gives a more natural colour.

The disposal of phosphor and the small amounts of mercury in the tubes may also be an environmental issue in some areas.

High Intensity Discharge (HID) bulbs — found in some high end dive lights — differ from incandescent bulbs because they produce light by creating a tiny spark between a gap in a pair of electrodes, which heats a gas in the bulb to a temperature where it emits an extremely bright light. They are also used when a high level of light is needed over a large area.

Compared to fluorescent and incandescent lamps, HID lamps produce a much larger quantity of light in a relatively small package. There are many different types, like mercury vapour, metal halide, high-pressure sodium, low-pressure sodium and less common, xenon short-arc lamps, which are used in operating theatres, or for lighting on movie sets, because they provide excellent colour projections and flesh tones.

Light sticks are becoming increasingly popular amongst divers and backpackers overnighting. By snapping a light stick, they have an instant, extremely lightweight, source of light. A lightstick consists of a transparent plastic tube that contains chemical fluids that are held apart in two compartments. The inner compartment breaks when the lightstick is bent and when the two chemicals mix, the reaction emits light, but not necessarily heat. The industrial strength lightsticks used in the outdoor industry can emit a useful light for up to 12 hours.

Pros: Lightsticks are ideal for carrying in a backpack or for diving as they are lightweight, weatherproof, non-toxic and nonflammable. They are easy to use and require no batteries. They are small enough to carry as emergency back-up on all trips.

Cons: Once used, its broken. The amount of light they provide is very limited.

Light Emitting Diodes (better known as LEDs) differ completely from incandescent or gas light bulbs, as they do not have filaments that can break or burn out. Therefore they last very long on low battery power — which contributed to their popularity for use in headlamps and just about every make of torch, diving or cycling light.

A LED is a special kind of diode (a diode only allows a power current to flow in one direction) that has the unique side effect of producing light while electricity flows through it.

An LED is made with two different kinds of material that carry electrical current: one type that has too many free electrons, and another that doesn’t have enough free electrons. Electrons from the over-supplied material gets pushed across a thin barrier into tiny spaces in the other, and a particle of light is produced.

The colour of the light depends on several factors: the chemical composition of the material it passes through, and the wavelength, or the amount of energy used to cross the barrier.

For example: if the band gap is small, fairly weak electrons can cross, and a dimmer red or infrared light with a longer wavelength is emitted. On the other hand, a large band gap that can only be crossed by the strongest electrons will emit a strong blue or violet light.

The different light colours emitted by LEDS would have the following benefits in the outdoors:

White light is all round the best colour for ordinary vision and gives excellent colour recognition. The modern bright white lights are brighter than incandescents, but not yet as bright as xenon.

In coloured light, everything is seen in monochromes.

Red: is best for night vision preservation at low lighting levels — for instance when a few friends go kayaking or fishing at night, the red light will prevent them from blinding each other, yet provide enough light to see if the fish are biting.

Amber: Focuses well in the eye and is usually a very comfortable monochromatic light to use in a group.

Blue: Good for hunters following the blood trail of wounded game. The blood shows up as solid black in this light.

In many torches and headlamps different colours of LEDS are combined so that the user can switch between settings.

Three primary types of LEDs are used in torches: 3mm LEDs are very small and are used in some of the tiny lights that produce little light (e.g. keyrings and novelty lights); 5mm LEDs are most commonly used in flashlights; while Luxeon LEDS are very bright (almost as much as incandescents) and big.

Luxeon LEDs have improved light output, sometimes as much as 5-20 times brighter than standard LEDs.

When several 5mm LEDs are used together, a good amount of bright light can be produced for a very long time. But the light beam from 3mm and 5mm LEDS cannot be well focused. Luxeon LED lights are focused better when using special optics or reflectors. But, their battery life is not as long as that of 5mm LEDs, although they last longer than incandescent lights.

Pros: LEDs last and last. They burn much longer than incandescent bulbs at their rated power — typically 10 years, twice as long as the best fluorescent bulbs and 20 times longer than the best incandescent bulbs — and can last 5 – 10 times as long on a set of batteries (eliminating the need to carry too many spare batteries).

LEDs gradually dim over a period of time, and will not abruptly switch off when, for instance, the filament breaks… a caver or hiker will therefore not suddenly be left in the dark in precarious terrain because his light source has burnt out.

LEDs are insensitive to vibration and shocks, and can therefore safely be carried in backpacks, without fear of becoming damaged. They can operate in temperatures ranging from -40° to as high as 80°C.

They light up very quickly and can achieve full brightness about 10 times faster than a normal incandescent light bulb.

Most high brightness green and blue LEDs, and all of the usual high-brightness blue-green LEDs, have a spectrum that is much more nightvision-friendly than the usual light spectrum of incandescent lamps. White LEDs, on the other hand, have a spectrum somewhat more favourable to day vision than the spectrum of typical incandescent lamps. In dim light conditions, white LEDs can usually outperform most incandescents watt-for-watt.

The even, clear light produced by some LEDs is brighter than light coming from the standard incandescent bulb.

Cons: The light beam produced by LEDs is, however, considered to be less powerful than incandescents — although that is fast changing with the latest models coming on the market — and more of them are required to produce the same amount of light.

LEDs are currently more expensive than more conventional lighting technologies. Since it takes a thousand or so 5mm LEDs to equal the light output of a 100watt light bulb and LEDs are expensive, LED is generally not the way to go for lighting a large area, like a campsite.

LED technology is, however, constantly evolving.

For instance, in the 6 years since the first Tikka headlamp with LEDs was introduced, Petzl has been able to improve so much on the LED technology that the current Tikka shines three times brighter than the original.

They have now developed their LED technology even further by this year introducing a new generation of 5mm LEDs that shine up to 80% further than the previous models in the compact Tikka and Zipka and the hybrid Myo headlamps, and 30% further in three of the special purpose Duo models.

What’s more, the light life on the maximum brightness setting is considerably longer. (This is not applicable in the Tikka XP and Myo XP, which use another type of LEDs).

For example, the Tikka Plus, which until last year emitted a white light beam of 17m, will now shine up to 32m — and the light duration when set on maximum increases from 80 to 100 hours.

In order to make their compact headlamps even more user friendly, Petzl now makes it possible to remove the new Tactikka XP Adapt from a headstrap and to attach it to a jacket or belt or cycling helmet — and the Zipka or Zipka Plus with retractable battery cords are so small and light that they can even be attached to a wrist, or anywhere else where light is required.

Universal models like the new Myobelt XP, with a choice between a wide-angle beam or high-powered LED with three lighting levels, work on a rechargeable battery that is carried separately and therefore does not increase the weight of the headlamp. In boost mode it can shine as far as 65m for up to 20 seconds.

Special purpose headlamps, or hybrids, provide the best of both worlds in that they combine a focused long range halogen beam to light up a larger area, with long-life LEDs that work well at close proximity — although these headlamps have to sacrifice some of their lightweight and compact benefits.

Petzl’s heavy duty special purpose headlamp, Duo, now comes with 14 and 8 LEDs — entry level models can be upgraded — and several models now work on rechargeable batteries. The larger capacity batteries can be worn on a belt, in a pocket or even in a backpack, to reduce weight. The IP X8 is waterproof down to 5m.

Princeton Tec, originally known for their dive lights, have produced several highly rated best of both worlds lighting products that combine the spotting benefits of incandescents and the battery conservation of LEDs. The waterproof Yukon headlamp, for instance, contains 3 LEDs for low light use and battery conservation, as well as a xenon pin bulb for when a more focused, brighter light is needed. In the new generation Yukon HL, the xenon bulb has been replaced by a Luxeon Star (side emitter) LED with reflector that can be focused when a brighter light is required, and which provides a longer lasting and brighter light than the xenon.

The website gives full marks to the Princeton Tec Apex that combines four 5mm LEDs with a Luxeon III LED focused beam, both with two output levels, and each with a separate switch. It also has a battery level indicator and a heatsink at the back of the head to draw heat away from the LEDs so that they can run at higher than normal output levels.

The Princeton Tec Pilot is a single 5mm LED light that can be attached to another headlamp strap or backpack with a moulded clip, to be used as a pivoting secondary light, or as a back-up light source in emergencies.

The benefits of LEDs are, however, not only used in headlamps. The Princeton Impact XL flashlight with a Luxeon Star bulb and reflector is, for instance, designed for good light output as well as long battery life.

The designers at US mountaineering gear manufacturer Black Diamond have designed their headlamps based on their experience in the field. The very highly rated Supernova (see is a hybrid that have placed 2 LEDs for close-up work and an incandescent bulb for when a larger area needs lighting (e.g. hiking) or a focused beam is required for spotting, on one bezel. A digital regulator makes it easy to select from the three levels of brightness offered by the 2 LEDs, as well as the incandescent — lighting up an area of 100m for 3 hours, 70m for 5 hours and 50m for 10 hours, or alternatively, enjoying 500 hours of LED light with 10m reach.

The comfortable and water resistant Helion is a 3 LED/xenon hybrid, providing either a long lasting (220 hours battery life) even light spill in LED mode, or a focused spotlight (xenon) with bezel adjustment.

The Swedish outdoor manufacturer Silva, locally distributed by Lynx Optics, has three different series of headlamps on the market to provide for every kind of activity.

Despite its compact design, the low weight L-series is robust and will withstand all weather conditions — rain, snow or heat. In the M-series the good light beam provided by halogen technology is combined with the long life of LED lamps for those who need to do close range work over a long time.

The Silva high-power series will appeal to those customers who want to light up a large area — like adventure racers, mountain bikers or rescue teams. The powerful 10watt and 20watt halogen light bulbs, aided by large reflectors, will turn night into day.

The various light mode options on most headlamps (power save, medium, bright and blinking) offer a versatile selection to suit every need — from the L1s very bright long range (63m) beam (made possible by the Luxeon LED bulb) with a life of 200 hours in power save mode, to the ultra bright 43m long beam provided by a 4 watt halogen lamp, combined with 3 LEDs that can burn for 100 hours with rechargeable batteries in the M1; or the extreme, but short-lived, 20watt halogen beam of the high-power 480 or 478 hybrid lamps that can light up an area of 110m for half an hour at a time.

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