Sign up for our newsletter


Technogram: Front light

James Spender
19 Feb 2016

Cyclist takes a closer look at the complex insides of your bike light

The changing of the clocks is still over a month away, which means that riding in the dark is still a daily reality for a lot of us. But what exactly goes on inside the shells of our road-illuminating companions? With electroluminescence, microchips and ingress resistant toggles, today’s bike lights are a paragon of technological modernity. Plus, they’re the only part of cycling where ‘doping’ is actively encouraged – through a process where impurities are added to semiconductors such as LEDs to increase their conductivity. So what’s responsible for all those lumens? 

The output of most high-end lights is regulated by a pre-programmed driver board (9), which in the case of Four4th’s Holy Moses light (pictured) helps prevent overheating when the LEDs (4) are being pushed to a massive 2,500lm brightness. (In this picture the LEDs have been flipped for illustrative purposes.) Minute screws (2) hold the LED board in place, while small plugs and wires (7, 8) connect the LED board to the driver board and the driver board to the switch (14) and power socket (13). A metal disc (5) sits on the back of the LED board and helps conduct away heat. Spacers (6, 10) keep parts in position, while up front a collimated polycarbonate lens (3) focuses light into the desired beam pattern and is held in place by a retainer (1), which screws into the CNC’d aluminium casing (11). The unit is powered by a cell or group of cells, which in this case takes the form of an external, rechargeable lithium-ion battery pack (15). Rubber seals (12) protect the unit from dust and water.

Top tips for bright eyes

A) LEDs generate heat yet can be damaged by excess heat. More powerful lights should be self-dimming to prevent LEDs reaching harmful temperatures.

B) When storing lithium based batteries (li-ion or
li-polymer) for a long time (eg over the summer months), partially discharge them to around 40% and keep in a cool place. 

C) Lithium-based batteries prefer not to be fully discharged so keep them topped up. However, it’s not necessary to fully charge them every time – charge cycles can be interrupted without detriment.

D) IP ratings (Ingress Protection) indicate a light’s level of protection from the elements. IP67 is a good benchmark (6 = no ‘ingress
of dust’, 7 =  no ‘ingress of water in harmful quantity…
up to 1m of submersion’).

Pictured: Four4th Holy Moses front light, from £275,

Read more about: