Carbide-free caving lamps?
A feasibility study
Carbide lamps have been used for quite some time now (since when? Beginning of last century?). Cavers in Switzerland still use carbide lamps as their main light source. Although they may seem archaic, carbide lamps have some distinct advantages that make them particularly adequate for the hostile cave environment:
- The energy density of calcium carbide is very high - you can easily carry carbide for several days of light
- The lamps are simple, indectructible unless directly hit by a thermonuclear detonation
- Problems are very often easily fixed in the cave using a swiss army knife
- The light is warm and pleasant
- Carbide can be stored in depots for long amounts of time (bivouac)
- The gas generator gets hot, nice for warming in cold caves
It is important to remember that light is not a luxury item. In most caves, without light you're dead. A reliable lamp is very important. But there are also several disadvantages:
- It's a mess - both when refilling the generator and where the remains are left (cave or somewhere in the landscape)
- Generator is bulky, awkward with the hose
- The gas stinks and is poisonous (nasty in narrow crawls when the lamp goes out)
- You can burn yourself with the flame (also often when crawling)
- The flame can leave ugly sooty patches on the ceiling
Why not using electric light?
It's mainly a matter of energy density. Until recently, it was impossible to carry enough batteries to have sufficient light for several days. But things change. Due to (not only) technological improvements, both the lamps and the batteries have now sufficient performance to think this carbide thing over again.
The LED revolution
LEDs have gone a long way since their appearance as dim red power-on indicators. Nichia was the first manufacturer to develop LEDs which were not only white but also had high efficiencies (14 lm/W) that made them useful for lighting purposes. For comparison - halogen incandescent lamps have efficiencies of about 15 lm/W, if operated exactly at their optimum operating point (this is why battery-driven halogen lamps are usually far worse). Flourescent lamps (what is commonly referred to as “neon lamp” - there is no neon insidem but low pressure mercury vapor) reach 40 lm/W. Sodium low pressure lamps (the yellow zebra-crossing light) even achieve 200 lm/W! So what's the big deal?
The point is that LEDs are available with very low power ratings. Flourescent lamps would be more efficient, but typically start with wattages around 10W. This is far more light than necessary. LEDs however, are available in 1W-5W versions (the luxeon LEDs), which is exactly the right amount of light. Even more, they can be dimmed without losing efficiency (in contrast to incandescent bulbs). New luxeon LEDs like the 3W star even achieve >25 lm/W efficiency.
The real thing: Bärenschacht
Before coming to the power sources, let's define a benchmark for an electric lamp: When would we think it is suitable for caving? The most demanding situation I know are the Bärenschacht expeditions. The Bärenschacht is a rather large system where you have to bivouac for typically a week to do any real work. Obviously, you cannot recharge the batteries in between - you have to stay in the cave. With carbide, this is no problem, you (or others who were there before you) can carry the necessary amount of carbide. An electric lamp dealing with this situation should be able to deliver at least 10 hours of bright light for seven days (you don't need maximum power all day - like breakfast, cooking etc).
So, how much energy would we need? From my experience with various LED lamps, I'd say 30 white LEDs running at 20 mA would probably be equivalent to an average carbide lamp. Assuming a converter efficiency of 80%, this would result in 2.5W. A 3W luxeon LED (still brighter) with a super-efficient 95% converter would require 3.2W. 10 hours with these lamps require an energy amount of 25-32 Wh. For seven days, this sums up to 175-224 Wh.
The battery (r)evolution
The newest LEDs give you enough light - if you have the power. Electrical power in this context... Batteries (primary and rechargeable) have evolved over the past years, driven by the increasing power demand for cell phones, PDAs, digital cameras etc. The most interesting technology (which is not really new) is Li-Ion. These cells have been developed for Laptop computers and cell phones, where space and weight are critical factors. Li-Ion cells are small and lightweight. But they are also very sensitive to overcharging and deep-discharge. A single overcharge can destroy a cell (legend says the cell can explode), as can a single deep-discharge. For this reason, all battery packs are equipped with a protection circuit, which at least monitors cell voltage and switches the cell off (using built-in MOSFET switches) when the cell voltage is outside its specified limits. Charging is also tricky, Voltages must be precise to 1%. And, finally, they are very expensive. That was common belief, until the real revolution started. With ebay growing from a flea-market place for old records to a platform for all kinds of internet dealers. There, a completely new type of dealer came to life: Ultra-cheap, high volume direct vendors. They sell hundreds of thousands of items mainly using automated software procedures, buy in huge volume in Asia and can, because of the high volume, live with very low profit per unit sold. Conventional dealers (with real shops, sales guys and such) need a much higer margin to be profitable. The really interesting thing is the resulting price level of Li-Ion batteries, which are one focus of these types of dealers. For example, the battery for my Canon digital camera costs 150 Fr when you buy it from Canon, a noname Product with higher capacity and working (mostly) as well is sold at 10 Fr. Of course, Manufacturers insist they have a higher quality levels, better protection circuits (preventing an overcharged cell phone from exploding), but this is obviously just a weak excuse for their rip-off prices.
Anyway - the important point is: Any type of Li-Ion battery used in digital cameras is available dirt cheap nowadays. As the battery packs contain protection circuitry and you own a charger already (if you have a digital camera) or can buy a charger for not much more than two batteries cost, we now have a high performance battery system at ridiculously low cost.
Here's a comparison of some battery candiadates:
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All prices are from cheapest internet or ebay dealers. At a local store, you pay typically several times the amount.
- The AA NiMH cell (price from fitformobile/ebay) is surprisingly good - both in terms of energy density and cost. But they are relatively large and have a low voltage, you need at least four to power a white LED with a step-down converter.
- The BP-511 pack is used in my digital camera (and many other Canon products). There are countless other camera batteries with similar properties. This single, tiny battery is sufficient to give you about three hours of light!
- As a comparison, the Sub-C cells are more expensive and heavier
- the 2CR5 lithium primary cell (standard photo battery, non-rechargeable) has half the weight compared with BP-511 or AA NiMH cells. And, still better - it can easily stored for ten years. This would be good for a backup battery you can store at a bivouac or keep in your kit (at 40g, not really significant. 70 cm of dry rope weighs as much). But it's not rechargeable, rather expensive for permanent use.
One-day-trip
Let's say, we are doing a one-day trip with an electric light. We are using a 3W luxeon or a 30 LED lamp and for simplicity assume we need 30 Wh. This is ten hours running the lamp at it's maximum setting (which is hardly necessary, I think). How much batteries do we need and what is the cost?
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Although NiMH is acceptable, handling so many cells (and you should always keep sets of four together - assuming the lamp is running on four cells) is a bit awkward. The price for the Li-Ion-cells is hardly noteworthy (remember, they are rechargeable!).
Seven days - Bärenschacht expedition
Where do we get if we need light for a whole week? The calculation is 30Wh*7=210 Wh:
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The interesting point is: Going on this expedition with electrical light, we'd have to carry 23 BP-511 batteries, weighing 1725g. This is not nothing, but possible. We'd have to invest 138€, around 220 Fr., for these batteries. As a comparison, upgrading a single Hilti TE10A battery pack using new 3.5 Ah cells costs you nearly 300 Fr! Would you buy the original BP-511 in a regular computer shop, this would set you back 2760 Fr. (BTW, Fr means swiss francs).
Conclusion
Caving without carbide light is now possible, thanks to new LED technology and el-cheapo internet prices for advanced batteries. Daytrips are easy and even one-week expeditions without being able to recharge the batteries seem possible. Li-Ion packs are preferable over NiMH due to smaller size and ease of handling. If you like the LED light - blueish compared to the warm carbide light - is another matter.