For an executive summary, read only the bold items. 


Why a pocket flashlight?

Flashlights seem like a non-important accessory, but in modern society, despite the brightly lit cities we live in, most artificial light come from a direction which creates blind spots by shadows: for example looking for an item at night in your car's trunk, something has rolled under a table, you are in a club and have to read something on a label.  If you frequent the outdoors or travel to state parks, artificial lighting if often kept to a minimum and encounters with caves, caverns, holes, tree trunks, looking under debris, etc., can be aided immensely with a bright light, even during the day, when one wouldn't consider lugging a flashlight.

Thus, a flashlight can be useful to have in your pocket as every-day-carry, EDC, if it were no bulkier than a wallet or a set of keys, but for decades this was not practical because flashlights were big, and non-LED bulbs produced a yellowish light that weakened quickly.  So one purposefully brought a bright bulky light when the need was likely, such as left in cars for emergencies or going for camping trips, anything else would be impractical.

Light emitting diode , LED, based lights appeared over 10 years ago, offered lower power consumption than traditional incandescent bulbs but also lower lumens.  However, the low power consumption made it practical to make very small pocket lights, no bigger than 3 stacked quarters for example, to make carrying a basic flashlight everyday, a reality.  Lights like the Photon became popular, and ran off button batteries.  Unfortunately, typical LEDs has permanent diffusers that made it difficult to focus, so the light was more like a candle than a focused beam; and had limited application.

Around the same time, Maglite made the AAA powered Solitare, an incandescent bulb light but with a focusable lens that made its weak lumen output brighter when focused and more practical than the Photon.  However, its incadescent bulb limited its battery life, and the brightness dropped as the battery voltage dropped.

Since 2000, great strides have been made in LED technology, were today they are being considered as replacements for compact flourescent bulbs, which only recently just began replacing all standard electrical lightbulbs.  These new LED provide over 3-9x the lumens of the Photon, have focusability, lower power consumption than an incadescent bulb and incomparably, have near white spectra, meaning light closer to sunlight in appearance.  Gone are the bluish tinge of 'white' LED or the yellow of incandescents.


LED Powered Lights

Today's LED powered lights are built in 2 ways: the simple direct connect to the battery via a switch; or with electronic circuitry, which maximizes battery life, allows adjustable brightness output to conserve power, or different modes such as strobing for use as an emergency beacon.

Taking after the Maglite company success and given a common use for most flashlights is during emergencies, many EDC designs are made to be tough:  aluminum bodies for housing, mounts for shock, and waterproof seals.

Users can be confused by identical looking lights: one may cost $3, while another is over $50.

Cheaper lights do not have electronics, use low lumen LEDs,and as the battery is consumed, the light output drops like a old style incadescent light.  The electronic versions cost more, but they are able to regulate power consumption, such that they can easily exceed and sustain brightness on their power supply, such as a single battery, and still get far over 2x the burn time of non-electronic lights.  Lights for emergency use should have long burn times, an ideal minimum is ~ 12 hours, the length of one entire evening.

Cheaper lights can be built of aluminum and cut to look like expensive lights, but the difference is in the details: the switch is not military quality, there are no waterproof seals, the case isn't designed to be dropped and a short shock could dislodge the LED mounts, electronics, or power connections.  If the light wasn't designed to be tough, it could fail when you least expect it, and when you need it most.



LD01 R4

Fenix LD01 is only 1/2 length longer and 2mm wider than the AAA battery it uses.  It weighs less than an AAA battery. This makes the light about as big and heavy as a pack of chewing gum.

It claims to be waterproof past 3+ feet and drop rated from 5 feet.   Although not meant for diving, my light easily take drops into puddles, survive rain, and falls into hard floors from about pants pocket height.  As a test I've put it in a glass of water without issues.

It can cast a beam to 150 feet, with a maximum output of 72 lumens and an intensity to 622 candela.  The light easily provides illumination while running or cycling and the focus mechanism provides an intensity similar to that of the Maglite 3x D cell incandescent flashlight.

My real world tests show the current draw is ~ 36mA, 360mA, and 1000mA for the low, med and high lumen settings.  From there you can estimate real world burn time with your battery.  For example with a 800mAH NiMH battery, burn time would be about 22 , 2.2, and 0.8 hours for each of the 3 power settings.

R4 is the updated model number than means it uses a new LED, in this case the Cree XP-G R4, which is more efficient that the predecessor LD01, called the R2 and the Q5.  However, this designation is not etched on the product or its packaging.  All new LD01 are sold as the R4, but its impossible to tell unless you check the power drain versus lumen output of your model.



Operation

The LD01 uses "twist" on/off.   Its not really a switch; you partially unscrew the headpiece so it no longer makes contact with the battery to turn it off.  Such design requires more grooves cut into the light to serve the switch function while still keeping the light together.  An O ring is usually recessed at the top of the body shaft so it makes contact with the headpiece early to keep the head water tight.  Twists are a very reliable switch design as it has virtually  no wear.  They are easy to maintain as as worse, all it needs are the battery contacts cleaned and the spiral grooves lubricated to avoid all wear, and this can be done with each battery change.  Other switches like sliders or push button have limited numbers of operations and typically fail when the return spring fatigues, the slide contacts loosen or the rubber coating punctures or wears from use.  In my 30 years of using flashlights, and particularly high reliability scuba diving versions, the twist ons types have never failed.  I use silicone grease to lubricate all o rings in my flashlights as its inert to all materials and non-toxic and reduces twist force needed to operate the light.

The LD01 has a cleaver brightness adjustment.  Simply turn the light on then off; if you switch it on again within 2 seconds it will toggle to the next brightness mode.   It has 3 settings: low, medium and high  outputing 3, 26, and 72 lumens respectively.  The medium setting turns on first, and can be used for everyday task.  I use the low setting for working in totally dark scenarios like working on moonless nights or inside a cave.  The maximum brightness setting works well for examining details of items or supplemenal light during the day.

The casing is made of aluminum.  It has a good feel and provides it its toughness.

Fenix claims the Cree LEDs used have a 50,000 hour lifetime.  This doesn't mean the LED will fail, but that the LED will output the specificed lumens during this period; thereafter it may drop in half but still work; compared to incadescents which would burn out in only scores of hours.   However, folks should know the electronics in the light is more likely to fail than the LED because overall quality control in electronics parts manufacture no longer targets 'best possible' but are designed to survive to about 5-10 year calendar lifepsan, when the devices they are used in are very likely obsolete, so why make parts last longer than this period?  Cree literature states if the LED is operated at under < 30 degrees celsius, at 85% humidity and current draw kept ~ 50% of rated capacity,  the lifespan of an LED could be unlimited.


Real World Reliability

The LD01 model has been around since 2008 and has been well received.  Since then, minor enhancements were made to reduce flickering and improved the lumen output, but the light has lived up to all its published specifications.  It has received consistently high reviews elsewhere.


Obsolescence

High lumen LED lights evolved since 2000 and many generations of LEDs have become obsolete as newer LEDs have higher lumen output per mA.  However, the rate of increase has plateaued.  Its not likely that more gains in lumens will occur without a rise in power consumption, which will challenge the practicality of an AAAx1  powered item, so its likely the LD01 design is mature compared to its predecessors.  In fact, the LD01-R4 has slightly less lumens than its predecessors.


Conclusion:

The LD01 appears like a regular flashlight, but represents  newer generations of flashlight capability.  I perceive its LED as mature and is unlikely to be obsolete for an AAA design; its built to last a lifetime, and will likely remain a viable performer to consider spending $40 on a pocket flashlight. 

The Fenix literature is confusing regarding this LD01 model.  The older models are rated at maximum to 80 and 85 lumens, but with shorter burn times;  the full designation of the latest model is LD01-R4, but the product or its packaging aren't labeled as such, only the enclosed spec sheet will suggest its the newest version. 



Recommended: Yes