The LD01 has essentially the same design as the earlier L0D model, differences include a deeper textured aluminum reflector made possible by the use of a smaller XP-E LED. Externally the head has a clean clyndrical design with a band of knurling machined on for grip. The body of the LD01 is very small and slim, as expected from an AAA light. It disappears in your pocket if u happen to carry it along with your key chain, light enough to not notice it's there. Even more so if you choose to power it with a lithium AAA instead of standard alkalines or NiMH rechargeables. The entire light is coated in Type 3 anodizing. One thing to note is that the coating on the current line of Fenix lights is smoother and more shiny compared to the earlier LxP series of lights. Thankfully the body is a hexagonal shaped tube, and the head also has a band of knurling about 1cm wide around it which makes the twist activation comfortable and manageable even with greasy fingers. Overall the aluminum body is pretty thin to keep it's weight and size down. Inside the body is all nice and cleanly finished, at the head end you will find the PCB for the "+" contact and at the bottom of the battery tube is a spring for the "-" battery contact. This prevents battery rattle and gives good tension to the body when the head is loosened in "off" position. The threads on this light are almost perfect. They are very smooth and free from accidental cross-threading, you won't need to turn them counter-clockwise to get the threads to align. Throughout the entire testing phase of this light, I did not experience any sign of cross-threading. Finally, since the LD01 is just made up of a head module and battery tube, there's no tail cap. At the bottom end of the battery tube there's a hole for a lanyard or key ring, and also a notch for the key ring to allow the light to tail stand. The o-ring around the neck came very well lubricated too.

If you're unfamiliar with any of the terms used in this review, click here for explanations on common flashlight related vocabulary.

The LD01 has 3 output modes in the following order:

Off > Medium > Low > High

The small reflector does an amazing job of producing a focused from considering it comes in such a small form factor. The deeper textured reflector together with the XP-E LED does an even better job at focusing light in this small form factor producing a smooth spot and spill beam. The beam's color temperature on my sample is a slightly cool white.

The LD01 is able to function on a 3.7V 10440 li-ion cell while still maintaining it's different output levels. Output on High is incredibly bright when running on a 10440 cell. This also means that you have to be careful of over-heating due to the small size of the LD01, heat will build up pretty fast. Runtime performance on an AAA cell is good in terms of both runtime and regulation. Output is regulated via PWM which can be noticed on the low and medium levels.

The Good - Maintains good output, runtime and regulation on a regular AAA cell. well-focused beam profile from a light this size. Fit and build quality is great.

The Bad - Noticeable PWM effect on Low and Medium level in spite of the manufacturer advertising otherwise.

The Relative - Neutral white beam color. Some minor beam artifacts and slightly lopsided corona. Uses a twist activated switching mechanism. Able to tail stand.