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Body: The battery tube has a simple and clean looking design. There's only one flat face machined onto the tube, which is where the Olight branding is printed on. There is a band of knurling about 2cm wide for additional grip. The area towards the end is slightly slimmer, this provides good ergonomics for when you're holding the light in a cigar/pistol grip. The walls of the I20's battery tube is thinner than either the I10 or I15 models. The battery tube is wide enough to accommodate even the thickest 16340 cells without problem. The I20 has a raised ring machined towards the end of the battery tube which makes it easier to hold in a cigar grip. As with the head, coating on the battery tube is just as well done, smooth and consistent. The threads between the battery tube and the tail cap are cut very smooth. I noticed that the more force you apply while screwing on the tail cap, the higher the chances of it getting cross-threaded. Otherwise, it screws on perfectly fine and smooth. There a clip attached to the batter tube which allows the light to be carried head-down, and it is held in place by a retaining ring which also prevents the clip from sliding around. The tail cap has a hexagonal design similar to the head and provides good grip when unscrewing the tail cap for battery changes. Housed inside the tail cap is a forward push button switch module, thus allowing for momentary activation. Everything from its tension and positive tactile feedback, to the clicking sound it makes is identical, which is a good thing. The I20 isn't able to tail stand since the switch cap protrudes out slightly from the tail cap. 
Bezel/Head: The head of the I20 houses a unique reflector cup which is half smooth and half textured, similar to earlier Olight models. The smooth surface area reflects a highly focused hot spot for optimal throw, while the textured surface area smoothens out any artifacts in the spill region of the beam profile. Its an innovative take on reflector design and produces a beam that is characteristic of Olight products. The emitter is just slightly off-center, but not by much. On the exterior, the head has a thin band of checkered knurling which provides some grip when you're twisting the head. The Type 3 hard anodized coating is smooth and consistent throughout, free of scratches or smudges. The threads on the head are not too thin or too thick. The head's exterior is of a hexagonal shape which serves as an anti-roll feature.
Output:Instead of having pre-defined brightness levels, the Olight I-series uses twists of the head to smoothly ramp its brightness level up or down. The direction of ramping alternates each time you loosen the head. To set the brightness level, simply tighten the head when you reach a particular brightness level during the ramping sequence. The I20 uses R2-binned LED's providing an output range of 6 to 235 lumens, taking about 2.5 seconds for a full ramp sequence either way. The digital current regulated circuit provides constant light output on all brightness levels with no signs of PWM flickering. You can also activate strobe and S.O.S. modes by half-pressing the switch within 2 seconds each time.
The color temperature on my sample is a neutral white, just slightly cool when compared to sunlight white. The beam profile has a spot which is well-focused and the spill beam is smooth without artifact thanks to its unique reflector design. There is a slight dark area right in the middle of the hotspot, but its not noticeable in practical use.
Runtime is good for the intensity of light it outputs on the brightest level. Regulation is also maintained well on either CR123 or 16340 cells, although noticeably shorter with 16340 cells.
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Level
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Lumen
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Lux
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Runtime hrs. (advertised)
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I20 low
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7
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75.347
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70
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I20 high
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235
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2529.5189
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1.5
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Strobe
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SOS
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Switch: The switch is a rubber covered clickie and is fully recessed in the tailcap which allows the light to stand on end and be used as an electric candle. Despite the fact that the switch is recessed, it is very easy to use. Click on, click off. You can lock-out the switch by unscrewing the tailcap 1/2 turn. This will prevent accidental activation when packing the light in your backpack or luggage.
Batteries: For batteries, this light is approved
by the manufacturer for use with two 16340 750mAh or two CR123 1500mAh
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China