StenLight high power LED caving head light StenLight LED Caving Lamp

StenLight Caving Lamps - FAQ

The StenLight S7+ is a rugged, compact, high powered LED head-torch designed especially for the hostile caving environment. Mud, water, and shock-resistant, the S7+ was designed by cavers to address the shortcomings of conventional cave lamps.

We have compiled this FAQ to - hopefully - answer all the technical and general usage questions we have been asked about the StenLight over the years.

Key features:

  • Compact and extremely tough anodised aluminium case with twin LED beams.
  • Lamp unit weighs less than 125g.
  • Ultra-lightweight lithium-ion battery pack, designed to be helmet mounted: no more heavy belt packs and snagging cables.
  • Four brightness levels, from Low (over 28 days of light!) to Turbo.
  • Operates off any 6 to 18 volt DC power source; invaluable on long/deep trips where recharging is impossible.
  • Long throw, high durability magnetic switch (no moving parts penetrate the sealed lamp body), designed to be used with gloves.
  • Water-resistant down to 7 metres (20 feet).
  • Swivel bracket supports easy adjustment: light up your feet or the sky. Will fit any helmet designed for blade mounting, or use the optional headstrap.
  • Solid state and shock-resistant, with extremely long LED life (>20,000 hours).
  • Flicker-free all-analogue control circuit for constant brightness.
  • High electrical and optical efficiency make the most of your batteries (96% electrical efficiency from 7.2V, 93% from 12V).
  • Smooth, optimised beam pattern with user-swappable lens options; the optics can be customised to give one spot and one flood beam.
  • Temperature limiting to prevent overheating of LEDs or exterior.

Question Sections

General Questions

Q: Why did the StenLight disappear from the market for a while? Are you still committed to the StenLight?

A: It didn't really, we were always here supporting existing customers. We only took the existing products off the market because we knew that new and revised equipment was on its way. Caving is a small market and we didn't want to sell people equipment we knew full well would be replaced or upgraded soon. We'd rather lose some sales than a reputation! Unfortunately it took rather longer - about 12 months longer - for the new kit to be ready than we'd been told it might. And yes, we're absolutely committed to the StenLight!

Q: Can I use the revised StenLight lamp with my existing battery and charger?

A: Absolutely, everything is both forwards and backwards compatible.

Q: Can I use the new StenLight battery with my existing lamp and charger?

A: Again, absolutely, everything is both forwards and backwards compatible.

Q: Can I upgrade my existing StenLight to the latest specification?

A: Yes, we offer two upgrade paths. One for original Luxeon III lamps and one for later Rebel 70 / Rebel 100 lamps. The former is a little more expensive since it requires modifications to the PCB. Please see the StenLight Service & Upgrades page for more details. For help identifying your lamp please feel free to contact us.

Q: Can I use my StenLight for other sports?

A: Yes of course! We've always taken the point of view that if you're spending £300 on an LED headlamp you can use it for whatever additional activities you like. Be that walking, mountaineering, ski-touring or orienteering (we sell a comfortable headstrap), mountain biking (we sell a neat handlebar mount), picking grapes in your commercial vineyard (yes, really), horse dentistry (yes, really), at work or just to rummage around in the understairs cupboard. Claiming a caving lamp isn't suitable for other activities is just tosh. In our opinion anyway!

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Lamp Questions

Q: What emitter is used in the latest StenLight lamps?

A: Luxeon Rebel ES top bin grade emitters.

Q: How bright is the latest StenLight lamp?

A: Peak output is 500 lumens approx. Thermal limiting will kick in after a while and gradually reduce the output. See below in the 'Really Technical Lamp Questions' section.

Q: But other lamps are brighter?

A: Some are yes. But ultimately we're not interested in a lumen-war. We're interested in making a lamp that gets the light output / usability / reliability / cost balance right. Some other manufacturers may exaggerate their emitter brightness readings, or give the values before they have been attenuated by lenses or glass. We do neither, and our figures are deliberately conservative.

Q: Tell me about the switch, how does it work? How do I keep it clean?

A: The switch is a simple mechanical / magnetic affair. There is no physical connection from the switch to the inside of the lamp (eliminating any chance of water ingress via the switch). If the switch gets mucky with mud rinse the lamp under a tap and waggle the switch lever around. If it gets really gunked up then take the back of the lamp off (2 1/16" allen screws) and give it a clean - it doesn't take more than two minutes.

Q: So there is a magnet in the switch?

A: Yes, there is. A tiny little one. We appreciate this may not be ideal for surveying but we have more confidence in the long term reliability of our simple magnetic switch than we do in complex electronic ones. In practice we find the magnet deflects a reasonably accurate compass at around 12cm to 15cm. The StenLight was designed to be operated with gloves; more cavers wear gloves than survey. Sorry if that sounds a little flippant but if the magnet is a major issue for you then we have sufficient respect for your opinion to not try to convince you otherwise.

Q: What voltages will the StenLight work from?

A: The lamp will work from 6 to 18 volt DC. Be sure you have the polarity right before attaching non-StenLight provided batteries (please see the note at the bottom of the page).

Q: How big is the StenLight? And how much does it weigh?

Very small and light!

  • Weight 125g
  • Dimensions (main body) 55 x 35 x 22mm
  • Dimensions (including switch handle) 55 x 45mm x 43mm

Q: How many lumens - in proper detail this time.

A: More than many, less than some and probably enough for most:

  • Low mode 5 lumens
  • Medium mode 45 lumens
  • High mode 157 lumens
  • Turbo mode 500 lumens
  • Turbo mode (thermal limiting) 300 lumens*

* Thermal limiting designed to prevent damage through over-heating, in test reached after approximately 1 hour at ambient 73° Fahrenheit.

Q: And what about run times?

A: With the latest LG825 battery pack:

  • Over 28 days at the lowest setting
  • 54 hours at Medium
  • 14 hours at High
  • 4 hours or more at Turbo
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Really Technical Lamp Questions

Q: Why won't the StenLight work from batteries below 5.2 volts? In other words, why did you use a buck converter instead of a boost converter or buck-boost converter? Or, why do you run off a 7.2 volt battery instead of a lower voltage?

A: Boost converters are generally less efficient because they must suck a lot of current at a low voltage, and the resistance and voltage drops in the converter circuit take out a greater percentage of the power than for a buck (voltage reducing) converter. For substantial power levels, such as the 7 watts used to drive the LEDs in Turbo, the difference in efficiency is quite noticeable (typically around 85% for a boost converter, vs. about 96% for the buck converter we use). Operating from a higher voltage that is still close to the LEDs' actual requirements provides the best possible efficiency.

There are several types of buck-boost circuits. The most common types use dual inductors (e.g. a SEPIC or Cuk converter) or are inverting. Either type wastes 2-3 times as much power as a good buck converter.

The ideal class of buck-boost converter uses a single inductor but effectively has circuitry for both buck and boost built in, and uses either one as needed. These can achieve as high an efficiency as a dedicated buck or boost converter, but are expensive and typically limited to low voltage and power.

Q: What is a DC-DC converter and why does the StenLight have one?

A: A DC-DC converter directly converts a direct current (DC) voltage to a different voltage, without converting it to alternating current or using a transformer. Most DC-DC converters can use an inductor to store energy in a magnetic field during voltage conversion. "Switched capacitor" converters use a bank of capacitors to store it in an electric field instead, but they are less efficient and can't handle as much power.

The StenLight uses a DC-DC converter to very efficiently convert the battery voltage (typically 7 to 18 volts) to the voltage the LEDs need (ranging from about 5.4 volts on Low to 7 volts on Turbo). The DC-DC converter also provides current and temperature regulation at the same time, which ensures that the LEDs are always operated within their limits. This is most critical on Turbo mode, but all brightness settings are regulated.

Q: Why does high efficiency matter?

A: Higher efficiency means longer run time at a given brightness level from the same set of batteries. The difference in run time between 96% and 85% efficiency is not that dramatic - about 45 minutes of extra run time on the High setting out of more than 6 hours. But there are other advantages of high efficiency. The energy wasted in the DC-DC converter turns into heat inside the circuit, introducing failure modes and reducing reliability. The 85% efficient circuit must dissipate almost 4 times as much heat. A further advantage of high efficiency is that it can run brighter. Turbo mode is thermally limited after a few minutes of operation in still air. A 96% efficient circuit permits nearly all the heat to be emitted by the LEDs, while an 85% efficient DC-DC converter requires the LEDs to run about 11% less bright in order to maintain the same temperature.

Q: Why don't you offer nickel metal hydride (NiMH) or nickel cadium (NiCd) batteries?

A: The StenLight is perfectly capable of running from 7.2V or higher NiMH or NiCd battery packs. However, Lithium-ion provides more energy per unit volume and significantly higher energy per unit weight than either of these technologies. Lithium-ion also keeps its charge much longer. Finally, Lithium-ion is much easier to charge reliably regardless of its previous charge/discharge history. As the chargers for Lithium-ion and NiMH/NiCd are totally different, we have standardized on Lithium-ion for all of the batteries we offer.

Q: Can the StenLight be operated from primary batteries?

A: Yes, but if the battery can't provide at least 7 volts at 1 amp you will not get full brightness on Turbo mode. Also, an adapter or connector will be needed. We offer a 9V adapter to let you use an alkaline 9V battery as a backup. It won't run on Turbo very long, but will run on Low or Medium for many hours. We also offer an adapter for 6 AA cells.

Primary lithium cells and other more unusual batteries can also be used as long as they provide sufficient current and voltage. Be sure you have the polarity right before attaching non-StenLight provided batteries (please see the note at the bottom of the page).

Q: Why not use a smoothly variable brightness control?

A: Three main reasons:

  • It isn't really that useful
  • It makes it next to impossible to guess how long your battery will last
  • It requires either a potentiometer, which is hard to waterproof, or a CPU

Q: There are modern CPUs that are small, inexpensive, and very low power. Why didn't you use one?

A: The simple answer is that we didn't need to. Stensat Group has used similar CPU designs for some of its picosatellites, but we never found a compelling feature that couldn't be better served by our analogue circuit. If we find a future enhancement that justifies the extra complexity, space, and cost, we'll use a CPU.

Q: Why not use a single 5W LED instead of dual 3W LEDs?

A: Four main reasons:

  • The dual 3W LEDs are brighter
  • 3W LEDs are much more durable
  • Having dual LEDs permits greater flexibility with different lens combinations
  • Dual LEDs spread out the light source, reducing glare

Q: Why not use dual 5W LEDs instead of 3W LEDs?

A: We tested this, and found that it wasn't all that much brighter and got hot a lot faster.

Q: If people only rarely use Turbo mode, why not use two 1W LEDs or a single 3W LED?

A: Turbo mode is quite useful in many situations. We tested dual 1W LEDs and field testers much preferred the dual 3W variety.

Q: Why didn't you provide a mechanical focusing mechanism?

A: We've never seen a mechanical focusing mechanism that wouldn't have taken up far more space than our fixed optics. So instead, we decided to have a single optimized, general-purpose beam pattern that can keep the unit simple and small.

<< Back to Top  < Back to Really Technical Lamp Questions

Battery Questions

Q: What is the new battery pack made of?

A: The new battery pack is made of cheese. A really hard, solid cheese that can be easily milled to shape. No, not really, we just wanted to check if anyone had got this far down the page. In reality, the battery box is an injection moulded custom-made ABS battery pack for 2 x 18650 lithium-ion cells.

Q: How waterproof is the new battery pack?

A: 20 feet / 7m.

Q: What brand are the cells?

A: The cells are made by AA Portable Power.

Q: Are the cells loose or tab-soldered?

A: Tab soldered.

Q: Is the battery pack serviceable?

A: Yes, the battery pack is serviceable; the cells and the cable can be replaced if required.

Q: Does the battery pack have an o-ring seal?

A: Yes it does!

Q: What does the battery pack weight?

A: 140g

Q: What are the dimensions of the battery pack?

A: 87 x 36 x 48mm

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Cable Questions

Q: The new StenLight has a new cable type?

A: Yes, a new round cable type was selected after extensive tests showed it to be a very robust cable with more flexibility.

Q: Can I fit the new cable to my old StenLight?

A: Absolutely, please see the StenLight Parts page.

Back to Top Back to Cable Questions

Connector Questions

Q: What sort of connectors do the StenLight products use?

A: The StenLight uses Molex/Waldom 0.062" standard 2-pin connectors, which are widely available from most major electronics parts distributors as well as from us direct - please see the StenLight Parts page.

Q: Why have you stuck with these connectors?

A: Because they are small, lightweight and we really never have had problems with them.

Q: Are the connectors waterproof?

A: The connectors used in the StenLight products are not waterproof, true waterproof connectors tend to be very bulky and expensive; semi-waterproof connectors become full of water even at fairly modest depths, add bulk and weight and are harder to clean mud out of compared to the simple connectors on the StenLight.

Q: Can I use a StenLight under water?

A: Yes, the lamp and battery are rated to 20" / 7m. If you need to go through a sump or duck-under, just unplug the connector afterwards (when it is convenient), shake the water out of each side and then plug them back in. If subjecting the lamp to prolonged immersion try packing the connector with some dielectric grease. Take even more care in salt water as passing electric current through salt water will set up an electrolytic effect and corrode connector pins. We do not sell or support the StenLight as a diving or cave diving lamp.

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Charger Questions

Q: Does the StenLight CL84-1 Charger work from 220/230/240 volt AC power?

A: Yes, the charger works from 100 to 240 volts AC.

Q: The charger's LED is green, but when I use the battery it is not fully charged. Is this normal?

A: The charger's LED will be off only when it is not properly connected to an AC power source. If it is connected to a battery while not hooked to AC, the light will be green regardless of the battery's state of charge, and it will slowly discharge the battery. You should verify that the charger's light is green before connecting the battery.

Q: Is the charger CE certified?

A: Yes, and the US to UK adapter plug we supply pre-fitted is completely legal and meets relevant standards.

<< Back to Top  < Back to Charger Questions

Technical notes:

  • All runtimes are based on the StenLight LG825 2.5 AH 7.4V lithium-ion battery, fully charged.
  • Calculated based on LED output and optical efficiency of lenses and front window.
  • OFF mode consumes 25 microamps (typical) regardless of input voltage.
  • Consumption by lamp only – does not include battery self-discharge.
  • Turbo mode is typically limited to 4-5W for long-term use due to thermal limiting.

A few general warnings:

  • As with any portable lamp, keep alternate light sources with you at all times.
  • The unit will become hot if used in Turbo mode for a prolonged period. The temperature is regulated to prevent damage to LEDs and to prevent burns, but the lamp may be uncomfortable to hold, especially after an hour or more of TURBO operation.
  • Use only with approved batteries and cables; connection to third-party batteries and cables is at the owner's risk – be aware that some third party products use the same connectors with reversed polarity, which could destroy the StenLight unit and/or the third party battery and could cause dangerous overheating of the cable, lamp and battery.

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