The Fenix E01 is a very small, slim and light weight flashlight very similar in design to the Arc AAA. It comes in a variety of colors, the one reviewed here is in black. The head houses the electronics and 5mm Nichia GS LED. The reflector in this case is actually machined into the aluminum head itself. As you can see from the image to the right, the reflector isn't really a reflector in the traditional sense as it not polished and coated like a real reflector. This is because the 5mm LED used is already pre-focused as is. What the polished surface around the LED does it collect the small amount of stray light emitted from the LED. Compared to the pre-focused beam, this reflected light is relatively insignificant. The exterior of the head has a nice band of knurling which has quite a rough texture which is nice and provides good grip. This really helps since the E01 is a small light, and the the switching mechanism is controlled via head twists.
The battery tube of the Fenix E01 is a simple and clean looking piece of aluminum. The entire light is consistently coated in Type 3 anodizing. Externally, most of the battery tube has nice, diamond textured knurling on it with 2 flat faces machined onto either sides where branding is printed. Thanks to the ample knurling, there will be no trouble handling the E01 even with greasy hands, regardless of its tiny overall size. The threads between the head and battery tube fit well together. They're well machined, I did not encounter any grinding or cross-threading during tests. Inside, the battery tube is cleanly finished bare aluminum, with no machining dust and such. Right at the bottom is a contact spring for the "-" battery contact. This means that the battery will not rattle in either on or off position which is a nice touch. Right at the end of the battery tube is a 3-point protruding stand which allows the E01 to tail stand. There's also a hole which allows for lanyard attachments and such. There is no anti-roll design implemented on the E01's body which is understandable since it's designed to stay on a key chain.
I would like to start talking about the output capabilities of the Fenix E01 from a slightly technical perspective to clear up some common questions. The E01 uses the new Nichia GS LED which is rated to typically output 30,000 MCD at 20mA current (64mW at 3.2V). Of course this depends on the rank of the LED used, which is why some users have reported varying levels of output intensities between multiple E01's. A U-rank GS LED outputs between 15,500 to 22,000 MCD at 20mA, while a W-rank outputs between 31,000 to 44,000 at 20mA. As you can see, even within the same rank, there can be about 30% variation in output.
The E01 is meant to be a general use light which provides similar output to coin cell powered key chain lights such as the Photon Freedom. Be sure to keep this in mind when purchasing the E01 so that you do not expect the high output intensities which most of the other Fenix products are capable of. The output is more than sufficient for tasks such as reading maps or walking around in a pitch black environment. With my review sample, the beam profile has a slightly oval shape and a noticeable violet hue as with most 5mm LEDs.
The regulation provided by the E01 is good but was expecting slightly longer runtime. While the E01 is specified as being able to run for 11 hours in "sun" mode and 10 hours in "moon" mode. In this case the "sun" mode refers the the runtime graph below, perhaps the 10 hours rated output can be achieved with an AAA lithium cell. The "moon" mode is the trailing end of the output curve, in the case of the E01, its "moon" mode is about 0.5% of initial output intensity. Obviously this is really low and you literally need to have the E01 about 3cm from your subject to get any use out of it. I'm going into some technical details again now, explaining why I would have expected slightly longer runtime from the E01. At an ideal 100% efficiency, the E01 would be able to run for 15 hours in "sun" mode with a 800mAh AAA cell. As you can see from the runtime graph below, the E01's circuit is slightly less than 50% efficient. Considering their other lights which are capable of about 70%-80% efficiency, the E01 could have been better.
The Good - Solid build quality and cleanly machined. Ample knurling makes handling and activation easy. Light weight and slim design fits quite comfortably on a key chain.
The Bad - Runtime is slightly shorter than expected. Advertised overall runtime with the inclusion of "moon" mode is slightly misleading as it extremely dim, about 0.5%, compared to its initial "sun" mode.
The Relative - Beam has a noticeable violet hue and a slightly oval profile. Is able to tail stand.