Haitz's Law states that every decade, the price of LEDs have fallen by 10x while the performance (measured in flux per unit) has increased by 20x, for a given wavelength (color) of light.
REF:Watching bats can be a problem as they are dark coloured, very small, fly and change direction very quickly, and are seen against a background of dark trees water or dark sky. You need a light that is: directional, powerful, reliable, robust, lightweight, cheap, and runs for ages on AA batteries. New torches using Light Emitting Diodes (LED's) are improving very rapidly but we still need to make some compromises.
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LEDs are continuously improving. In 1999 their efficiency
surpassed that of conventional incandescent bulbs, and in 2006 Cree
demonstrated white light LEDs with a better efficiency than
fluorescent tubes. Haitz's Law states that every decade, the price of LEDs have fallen by 10x while the performance (measured in flux per unit) has increased by 20x, for a given wavelength (color) of light. REF: |
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Seoul Semiconductor have recently (Feb 08) brought to market the Z-Power LED P7 series a single LED package providing the worlds highest brightness of 900 lumens (90 lumens per watt) and lower power (1W) leds in development are now achieving up to 160 lumens per watt. (lm/W) (Jan 2009) By comparison our "low energy" light bulbs deliver 60 lm/W, and quartz-halogen headlight bulbs a puny 20 lm/W. (A lumen is the standard unit for measuring total light output, and a candle produces about 13 lumens) These developments mean LED's are now well suited to application for portable lighting. |
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One very advantageous feature to look for in a torch is the ability to choose a lower
light output. This FENIX L2D offers 12, 53, 107 and 180 lumens from a CREE Q5 LED and two AA cells. Power is selected by
rotating the bezel switch (separate from the on/off switch). Some torches require you to cycle through
the power levels - not much good if you are trying to preserve your
dark adaptation! "Led lenser" torches and some of the other high-end torches use a focussing lens that is matched to the shape of the led to give a beam that can be focussed from spot to flood! |
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This torch by XTAR
uses a SSC P7 900 lumen LED (shown above) driven from a single 18650
Lithium rechargeable cell to give about 600 - 150 lumens output. The run time is about 2h on a fully charged battery, or 20h on the low setting. It comes in two models, the P7-C and P7-C2. I chose the latter for a bit of "spill" - if a bat flies out of the beam this means I can see where its gone. It comes in a kit with two batteries and a charger for about £50 delivered. That might sound like a lot but its really good value for money, and easily outperforms my big heavy lantern. review here I got mine from Quality China Goods on Ebay |
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| There are some great deals (Ebay) for torches like these with CREE Q4 LED's and including 18650 Lithium AA cells and a charger for £20 inc p&p! Many torches that use 18650 rechargeables also let you use CR123's as spares.It is reported that some manufacturers are using cloned LED's and over-running them to get very high lumens ratings, (over 220) at the expense of their useful life. Beware of torches that use AAA size batteries unless size is really important, as the capacity of these is small compared to AA's. |
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| For hands-free use Noel recommends this Tikka Plus head torch from Petzl. (Amazon.co.uk £24) It offers three light levels and uses 3 AAA batteries. Don't use Lithium cells in this you will blow the LED's! |
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| If you want to keep your existing torch but change to using LED's you can get these Terralux LED bulbs which run from 2 - 9V and give 50 lumens. (£10)Also by Terralux LED converters to change any of the MAGLITE range to use high power LED'sCheck out http://www.thetorchsite.co.uk/index.html |
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| These all use a bulb with a tungsten filament, which radiate most of their output in the infra-red. To get better efficiency you need to run the filament hotter. But tungsten cant be used at much over 3000 degrees as it starts to evaporate weakening and eventually destroying the filament. Tungsten-Halogen are the most efficient, adding Xenon makes them even better. |
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| Lanterns rated at over a million candlepower mostly use 55W or even 100W car headlight bulbs ( shown above). The downside here is their limited burn time of about 20 min. This is down to the massive amount of heat they produce, and the size and weight of the battery needed to power them. Getting huge candlepower needs a powerful bulb, careful focussing, and a large reflector. This one weighs 4kg Lumens is a measurement of the total light output of the lamp, while candlepower is a measurement of the brightest part of a focused beam. |
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| This more "sensible" 100,000 cp type rechargeable lantern uses a 6V 4Ah gel cell and 6W flange type xenon lamp to give about 120 lm with a run time of about 4h continuous use. Its still bulky and the advantage of the bigger cell is reduced by the lower efficiency of the lamp as compared with the best LED's but this shape with a top handle is often useful, and it does have the advantage of being easy to charge, coming with both mains and in-car chargers. |
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Recently introduced headlight systems for upmarket cars use HID lamps at up to 35W to produce a staggering 2800 lumens. This technology has been adapted to make torches with high light output but a more realistic burn time. Usually powered by Lithium rechargeable batteries, they can still be rather heavy because of the electronics needed. Sorry no pictures as yet but for examples try here. http://www.hids-direct.co.uk/flashlight.html
The Great Internet Light Bulb Book http://freespace.virgin.net/tom.baldwin/bulbguide.html