[subwoofer]

Rather than a full in-depth review, this is a brief 'Performance Review' of the Fenix BT10 and BT20 bicycle lights.

I have run the lights through the same technical testing I normally carry out for a full review, and am presenting the results in a more concise way so you can easily see how they actually perform.



The BT10 and BT20 can comfortably be mounted on a helmet as well as handlebars.





Batteries and output:

The BT10 uses a 4xAA battery pack and the BT20 a 2x18650/4xCR123 pack. Either pack can be used with either light, but when using the BT10's pack with the BT20, the low battery light shows straight away.

The BT10's battery pack



The BT20's battery pack



One slight disappointment is the low battery warning, which does not help much. The BT10's switch stayed green all the way down to a very dim output. The BT20's switch went red after 36mins of Turbo, but then continued to output the Turbo level for a further 42mins with the low battery warning.


To measure actual output, I built an integrating sphere. See here for more detail. The sensor registers visible light only (so Infra-Red and Ultra-Violet will not be measured).

Please note, all quoted lumen figures are from a DIY integrating sphere, and according to ANSI standards. Although every effort is made to give as accurate a result as possible, they should be taken as an estimate only. The results can be used to compare outputs in this review and others I have published.

The BT20 on test.

Fenix BT10 4xAA Eneloop	I.S. measured ANSI output Lumens	PWM frequency (Hz) or Strobe frequency
Turbo	369	0
High	219	0
Low	83	0
Strobe	Not measured	6.8 and 1 mixed

Fenix BT20 2xARB-L2	I.S. measured ANSI output Lumens	PWM frequency (Hz) or Strobe frequency
Turbo	763	0
High	464	0
Med	306	0
Low	104	0
Strobe	Not measured	6.8 and 1 mixed

These lights utilises an electronic switch, so there is parasitic drain to consider.

BT10 – 0.5uA – 165 years to drain batteries
BT20 – 1.8uA – 456 years to drain batteries

The runtime graph shows the output traces for both the BT10 and BT20 running on maximum output and with a cooling fan.





Test sample provided by Subwoofer for use on my night time bike rides.