Has Murphy met his match? The battery-free flashlight

Surely the touchstone of Murphy’s Law is the battery-powered flashlight. When you really need one — to check the anchor rode in mid-gale or when spelunking the depths of the aft lazarette — the batteries either emit a dissipated yellow glow or they’ve expired altogether. It seems only obsessive checking and replacing can circumvent the perverse tendency of flashlights to harbor dead batteries.

A new product recently introduced into the marine market by Weems & Plath of Annapolis, Md., may, however, allow the flashlight to escape its dark, entropic fate. Even its name instills confidence that technology can vanquish Murphy: The NightStar Magnetic Force Emergency Light is not your ordinary flashlight. Instead of relying on all-too-mortal AA, C or D cells for electricity, it makes use of a magnet and a coil of wire to supply electrons to the light.

The concept behind this is called induction, and it is one of the manifestations of electricity’s and magnetism’s spooky, not-yet-fully understood relationship. If you take a conductor of electricity, like a length of copper wire, and move it through a magnetic field, a flow of electrons will appear on the wire, just so long as the wire is moving. The other way works, too; move a magnetic field past a stationary wire and again, electrons flow, so long as the field is moving in relation to the wire.

This induction mojo works both on a small scale in flashlights and at a mammoth planet-wide scale. The earth is surrounded by a magnetic field, and experiments have been conducted in orbit to test induction-based power production. Astronauts on the U.S. space shuttle reeled out a long, weighted wire from the cargo bay. As the shuttle circled the earth, the wire was moving through the earth’s magnetic field and electrical current was induced in the wire. Also, when powerful streams of charged particles from the sun hit the earth’s magnetic field, they cause it to oscillate slightly. This moving magnetic field then induces detectable currents on long conductors like, for example, the Alaska oil pipeline.

Induction is the essence of the NightStar flashlight, manufactured by Applied Innovative Technologies of Fort Lupton, Colo., and distributed to marine retailers worldwide by Weems & Plath. Electricity to power the light comes from a rare earth magnet composed of neodymium, iron and boron. As the magnet slides back and forth inside the body of the unit, it passes through a coil of copper wire, causing electrons to flow.

Of course, there’s a bit more to it than that. If you were to throw together a moving magnet and coil of wire and then connect that to a light bulb, you wouldn’t have a very effective light. The bulb would glow every time the magnet passed through the wire, but would go out as soon as the magnet stopped. A flashlight built like this would require constant movement of the magnet, and even then, it would produce a pulsed light.

The NightStar produces a steady light by adding a few more elements to the system. Every time the magnet/coil assembly in the NightStar produces a pulse of electricity, that juice flows into a solid-state device called a capacitor that can store electrical energy. A capacitor in its simplest form is little more than two metal plates separated by an insulator. Build up the charge on one plate, and the electricity will want to discharge itself to the uncharged plate, a process prevented, of course, by the insulator. A capacitor is discharged when a connection is made between the two plates. Since capacitors don’t use chemical processes to store electricity the way batteries do, they tend to be long-lived. The one-farad capacitor in the NightStar is rugged enough to be recharged/discharged several hundred thousand times. The last element that makes the NightStar a useful tool is the use of an LED light source instead of an incandescent bulb. An LED is more efficient and requires less power to produce the same amount of light as an incandescent bulb. Plus incandescent lamps used in flashlights typically have lifetimes of about 500 hours, while the LED in the NightStar will last more than 50,000 hours, according to Applied Innovative Technologies.

The body of the NightStar is clear polycarbonate/ABS plastic, and you can see the magnet moving back and forth as you shake the unit. Only 30 seconds of shaking the unit fully charges the capacitor, and then it only needs a shake for 10 or 15 seconds every 10 minutes to maintain the 10-lumen brightness of the light.

And if you ever find yourself in an emergency situation with a NightStar and no compass, you can reportedly suspend the flashlight horizontally, and the front of the flashlight will point to magnetic north. Of course, if an emergency does leave you adrift in a life raft, you’ll have a reliable flashlight — even if you run out of everything else.

By Ocean Navigator