On LED Flashlights…

By Bryan Geyer

The innate connection between a flashlight and “Audio Tech Talk” becomes apparent as soon as you try to inspect any part of your sound system that lies beyond the front panel. In recognition, here’s some personal guidance about the most vital tool you’ll ever need: A modern single-cell LED flashlight.

First, learn why the light emitting diode (LED), a semiconductor device that dates to the late 1960s, didn’t become abundant in flashlights until some 30 years later. What a curious delay! What happened? And what changed? Well, a modern “white light” LED won’t fire until it sees a threshold bias of about 3.2 volts minimum, and 4 volts or more works better. But a fresh single cell battery produces only ~ 1.2 to 1.7 volts, dependent on its chemistry (see footnote*), so multiple batteries would be needed to fire a solitary white light LED. Clearly, using more batteries than before didn’t advance the state of flashlight design, so miniature incandescent lamps endured. Then, barely before year 2k arrived, integrated circuit “boost chips” appeared. These new silicon ICs could efficiently elevate the energy from a single storage cell to the operating level needed to fire a white light LED. The basic design concept was old, but implementing it in IC form was breakthrough genius. The entire boost function, consisting of the surface-mount chip plus some tiny passive peripherals, could now be packed into a bundle smaller than the size of two stacked dimes. A practical single AA cell LED flashlight was suddenly viable, and its launch assured immense advantage over anything using an incandescent bulb. A lone LED could now provide more light (with selectable lower levels), draw less current, offer high resistance to shock and vibration, and assure decades (not hours) of maintenance-free service life—all while selling at competitive mass-market prices.

Product development was intense, with many players engaged. Some failed, some flourished, and several smart trans-Pacific sources became dominant. There’s now a wide array of LED flashlights and multi-LED lanterns on the market. Many designs serve niche applications, but my intent here is to feature a basic everyday flashlight—a modestly priced model that’s appropriate for general purpose use and practical in-pocket carry. A flashlight that…

…is short (≤ 3.1" long), skinny (≤ 0.75" diameter), and uses only a single AA size cell.

…is blindingly bright at full output, with multiple lower levels to conserve current drain.

…has long throw capability, with enough side spill to see the borders of your path at night.

…is obvious in operation, with a single butt-end control button for all switching functions.

…offers instinctive battery exchange: unscrew head and replace AA cell, button end up.

…has solid mechanical integrity; built to withstand the rigors of moderate abuse.

…if supplied with a pocket clip, such clip must be readily removable and leave no evidence.

… meets the IP68 waterproof standard (up to 30 minutes at depths of ≤ 2 meters).

…is cheap enough stash extras (toolboxes/cars/bikes/garage) and give as gifts.

There aren’t a lot of candidates that meet all of my objectives. Many come close, then fail the “side spill” criteria. That’s because flashlight marketers always hype throw (range), and inexperienced buyers focus on that feature; they haven’t yet grasped the importance of spill (beam spread). The two parameters (throw and spill) are mutually exclusive; more of one means less of the other. A very tight beam will deliver impressive reach, but hot spot fixation invites personal risk when you can’t see the edges of a narrow path from just one step away.

My pick as a good “everyday” single AA cell flashlight is the Fenix E12 Version 2.0. It meets all of my criteria, and you can buy it here: https://www.fenix-store.com, or here: https://www.batteryjunction.com The Fenix E12 V2.0 flashlight offers three selectable outputs: 5, 30, and 160 Lumens. It uses a cool white LED, and has an ultra-thin (3mm) optical front lens—all very desirable. The lowest level is appropriate for checking your watch in a darkened theater or finding a keyhole at night. The mid-level setting, 30 Lumens, assures a practical balance between output and capacity. It’s great for all of your “fix it” tasks, also for walking at night. The full 160 Lumen output provides a brilliant spotlight, but keep it brief! Apply only in 10 to 20 second transient bursts. At this level, supply current is consumed at a rapid rate, and there’s significant internal dissipation (heating). As with many LED flashlights, these output levels are all electronically regulated, so the lighting intensity stays constant; it won’t droop as the AA cell ages. Full expiration becomes suddenly apparent; it’s dependent on the drain that’s required for the level you’ve selected. When the supply current is insufficient for a given level, the output will drop to the next lower level. When it’s too low to maintain the regulated 5 Lumen minimum, the output drops to a useless glow, then goes out.

The Fenix E12 V2.0 flashlight comes with an attached (by compression) pocket clip that I dislike, so I trash it. This is easy to do with the aid of pliers—just grab the clip and pull it off. It will readily detach and leave no evidence that it was once mounted on the flashlight body. This flashlight is so small and light that a pocket clip isn’t of practical benefit; however, removing the clip will then expose a perfectly cylindrical body, and round stuff that’s not restrained can roll off flat surfaces. If this annoys you, consider mating a wrist strap to a rear lug. Straps that have a small pigtail loop at the end will pass through the lug without impeding the control button.

BATTERY OPTIONS: AA cells are readily available in the variants (3) noted below*, but you’d do well to reject the use of alkaline (manganese dioxide) LR6 cells. These conventional cells are very popular, but too risky to merit informed consideration. When an alkaline AA cell approaches expiration (output ≤ 0.7 volts), it will progressively destabilize and form a caustic compound (KOH, potassium hydroxide) that will penetrate the outer shell and attack anything that’s within reach. The consequent damage can be severe. This is an inherent flaw—all alkaline cells present this same inevitable hazard—so don’t use alkaline AA cells. Instead, select either of the other options. I use the non-rechargeable lithium-iron disulfide Class FR6 cells, e.g., Energizer’s “Ultimate”**. Others prefer the rechargeable nickel metal-hydride (NiMH) Class HR6 cells. Both options are safe, don’t leak, and work well. Non-rechargeable lithium AA cells exhibit extended operating life, perform well in cold ambients (alkaline cells don’t), weigh about 40% less than the alkaline equivalent, and can tolerate long term (10 years) passive storage with minimal (5%) net self-discharge. Buy in bulk, stow for use as needed.

* The nominal AA cell output voltage, when fresh (or freshly charged), is…

…1.5 volt for a non-rechargeable alkaline (manganese dioxide) IEC Class LR6 cell.

…1.2 volt for a rechargeable nickel metal-hydride IEC Class HR6 cell.

…1.6 to 1.7 volt for a non-rechargeable lithium-iron disulfide IEC Class FR6 cell, e.g., Energizer “Ultimate” AA cells.

IEC = International Electrotechnical Commission

 ** I buy on-line, from Battery Junction; refer… https://www.batteryjunction.com/energizer-aa-ln91-24pk-battery.html

BG (December 2022)