Advanced Lighting Products

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 plan to 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 will 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).

How do you take care of Li batteries?

What do you do if going into water?

The batteries are only water resistant. Do the Fallowing:

Where do you get dielectric grease?

Most auto stores carry it.

Why not use a smoothly variable brightness control?

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?

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.

Does the StenLight draw current when it is plugged in but turned off?

Yes, it draws a small amount of current in order to be able to detect when you turn it back on. But this current is extremely small (about 25 microamps, less than the self-discharge rate of any rechargeable battery you're likely to connect to it). If you are likely to keep the battery on the shelf for 6 months or more, you might as well unplug it, but otherwise it's not an issue.

Does the StenLight have a setting for signaling SOS in Morse code?

No. Convince us why that would be useful and we'll think about adding a CPU to accomplish it ;^)

Does the battery protection circuit cut off when the battery gets too low?

In theory yes, but in practice no. The two LEDs are in series, and require 5.2V to draw any current. So as the battery starts to get low, it drops below 7V and Turbo mode is no longer full current (this happens at about 94% of discharge). As voltage drops further, the current keeps dropping faster. Below 5.3V the current is quite minimal, and eventually the LEDs are not driven at all (the converter will continue to run at about 1/3 of a milliamp). The end result is that as the battery draws down you get 30 minutes or more of gradually dimming light to warn you to change batteries.