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StenLight Technical FAQ

Why won't your light 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?) (In other words, why do you run off a 7.2 volt battery instead of a lower voltage?)

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 Mode, 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.

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

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.

Why does high efficiency matter?

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.

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

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.

Can the StenLight be operated from primary batteries?

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-Stensat-provided batteries (see the note at the bottom of the Fact Sheet for more details).

Why not use a smoothly variable brightness control?

  • 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

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

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 analog circuit. If we find a future enhancement that justifies the extra complexity, space, and cost, we'll use a CPU.

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

  • the dual 3W LEDs are brighter
  • 3W LEDs are much more durable (20,000 hours vs 500 hours at full brightness)
  • having dual LEDs permits greater flexibility with different lens combinations
  • dual LEDs spread out the light source, reducing glare

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

We tested this, and found that it wasn't all that much brighter and got hot a lot faster. Dual 5W LEDs would also be significantly more expensive and would have a much shorter operational life.

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

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

Why didn't you provide a mechanical focusing mechanism?

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.

Can I use the StenLight underwater?

Yes, but applying power to it for long periods of time will eventually electrochemically corrode the battery connector. This happens a lot faster in salt water (or in a washing machine) than it does in fresh water (minutes vs. hours). 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.