Quite how bright your lights need to be depends on whether you'll be cycling under streetlamps or on unlit lanes. Under streetlamps, you need to announce your presence to drivers.
With the evenings drawing in, it's time to find your bike lights and check they work - or to invest in some new ones. To ride your bike legally on a public road at night, you must have a white front light and a red rear light (in addition to a rear reflector and pedal reflectors).
The Road Vehicle Lighting Regulations (RVLR) say that you these lights should conform to BS6102/3 or an equivalent European standard. It's actually quite hard to find such lights in the shops, so it's no surprise that this nominal requirement is not enforced. Just use bright lights of the appropriate colour.
Seeing and being seen
Quite how bright your lights need to be depends on whether you'll be cycling under streetlamps or on unlit lanes. Under streetlamps, you need to announce your presence to drivers. On dark roads, you also need enough light to see where you're going. Most battery lamps from 150-200 lumens upwards will illuminate the road well enough 10 metres ahead; more powerful lamps allow faster speeds and more security. Note that really powerful lamps, intended for mountain biking at night, can dazzle drivers.
Flashing or steady?
Flashing lights have been legal for use on bikes since 2005. The vast majority are strictly road legal only if used in addition to steady lights and not on their own. This is not enforced; as long as they're bright enough and the right colour, the police seem happy whether they flash or not. In fact, flashing lights have now become associated with cyclists. They do make your presence more obvious but can make it harder to judge how far away you are and how fast you're travelling, so flashers make more sense on street-lit than unlit commutes.
Unlike dynamolighting, which is self sufficient, battery lights run down. This is less of a problem now that efficient LEDs have replaced incandescent bulbs and now that rechargeable lights are becoming more common. Yet you can still exhaust a battery light in a few dark journeys, particularly using a high-power mode. It's worth having a backup front light for all but the shortest of commutes. A head torch (e.g. Petzl) is handy. Rear lights draw less power and last longer; one commute is unlikely to see 'dimming' become 'dead'.
Rear LED lights are economical enough with replaceable alkaline batteries. Front lights are much more practical long term if they're rechargeable – either because they have an integral lithium-ion battery or because you've swapped disposables for rechargeables. Develop a charging regime, so it becomes habit. Many smaller lights charge by USB these days so you can top them up at your desk.
Finally, don't forget to unclip your lights from your bike when you park, and make sure they're not flashing in the bottom of your pannier all day!
Here's a selection of compact lights suitable for commuting.
|Moon GEM 1.0 front light|
This memory-stick sized LED light is ideal as a backup. It's bright enough to illuminate the road, not just blink, and its lens gives some side visibility. There are flashing and steady modes, with a low battery indicator. It recharges by plugging directly into a USB slot. Rain resistance is pretty good and the silicone strap fixes in seconds to any diameter handlebar.
|Lezyne Micro Drive LED front|
Despite weighing only 67g and being about the size of a single D-cell battery, like those we used to stick in our Ever Readies, this lamp emits up to 150 lumens. It'll do that for 2 hours or run for up to 6 on lower settings or high-powered flash. Its lithium ion battery is USB rechargeable. The CNC-machine body is sturdy and well sealed against rain. A helmet mount is available separately.
|Cateye Nano Shot EL620RC front|
Good enough to light your way on unlit roads, even at speed, this compact light puts out 250 lumens on high power. Run time is only 90 minutes like that but it will do 12 hours on less draining settings. The integral lithium-ion battery recharges via USB in 3.5 hours and there's a low battery indicator. For an extra £40, the Nano Shot Plus EL625RC offers up to 600 lumens.
|Smart 3-LED rear light|
Smart's seatpost-fixing 3-LED rear light has scarcely changed in years – a testament to a design that's simple, effective, and economical. Two AAA batteries are included and it'll last up to 200 hours before they need replacing, if you stick with the flashing mode. A steady mode is also available. Weather resistance is good. It will clip to the back of some panniers, backpacks and seatpacks too.
|Busch and Muller DToplight Permanent|
The best thing about this German rear light is that it fixes to a rear pannier rack. You'll need light mount (or an adapter) on the back of the rack with holes 50 or 80mm apart. Since it's bolted to your bike, you don't have to remove it to prevent theft when you park. Its two bright LEDs run off two AA batteries, and there's a large integral reflector. A four-LED version is available for an extra £3.
|NiteRider Solas 2 Watt USB tail light|
This new light from NiteRider uses a very powerful LED; 2 Watts may not sound much if you're used to incandescent bulbs but for a rear LED light its piercingly bright. In fact, its four settings (two steady, two flashing) include a 'group ride mode' to prevent dazzling riders behind you. Run time is from 4:30 hours on high power up to 18 flashing, and it's USB rechargeable. It fixes to the seatpost or a seat stay.