Basically there are two types of bike lights – lights to see by and lights that allow you to be seen.
Be seen lights
Bike lights that allow you to be seen are emergency lights for when there is sufficient light to see where you are going, e.g. if there are street lights, it is early morning/dusk, there is mist/fog, but you need something to warn other road users that you are there. These lights will not provide enough light to see by.
Even if you are not intending to ride in the dark you should have a set of emergency, be seen, lights. Fog can descend without warning on high ground, even in the summer, and if you are riding on busy roads even a little spray from wet roads can render you almost invisible. There were two instances on my end to end where I needed my lights, one due to for fog in Scotland and one due to spray on the busiest section of road I used on the whole route.
There are a number of be seen lights available, some so small and light you will not even notice that they are there. I use Knog frogs front and rear and, in addition, a Cateye TL-LD610 at the rear.
Lights to see by
Bike lights to see by mean just that. There are various options at a wide range of prices providing various levels of just how much you can see! As you might expect, the more you pay the brighter the light and the lower the weight (in general).
Dynamo powered – lights wired to a dynamo (powered either through your wheel hub or a friction mechanism resting against your tyre wall). These provide the convenience of instant power at anytime without having to carry batteries. You are the power source so there is a marginal amount of extra effort required (although with massive improvements in light technology, considerably less than a few years ago). The initial set up costs, especially for a hub powered system, may be higher than a battery light option.
Battery power – there are a wide range of battery powered lights that fall into two broad categories, rechargeable and non rechargeable. The benefit of a rechargeable light is that you do not have to keep buying new batteries, which can prove to be expensive. The disadvantage is that if your light runs out of power before you reach your destination you are a bit stuck (unless you have a back-up light). I purchased the very fine cat eye HL-EL610 rechargeable which provided very good visibility at a reasonable cost. Also, on low power, it provided several hours of light. However, the first time I used it for more than a commute, on a proper night ride (on the night leg of a 600km in South West England) I ran into a problem. I had accidentally switched the light on during the day without realizing it and when I came to use it there was only about 15 minutes worth of power left! All I had left were my emergency Knog frogs, which would keep me visible but did not provide anything like enough illumination to cycle by. I was forced to tag onto another rider and travel at his higher pace. The result was, by the time we reached the sleep stop, several hours later, I was cooked and had to abandon. The lesson learnt was to carry a back up light! (Incidentally the person I cycled with had his dynamo fail on him but he had a back up light).
I now have a Hope 1 which provides excellent light output. Level one is easily sufficient for road use and it has three more brightness levels above this. I have comfortably cycled downhill at 25mph + without fear of hitting unseen obstructions on level four. It also has a ‘be seen’ flashing mode. This is not a rechargeable light but I use rechargeable cells. I purchased 2 sets of four 3200 mAh AA cells for about £10 on-line. They seem to provide about the same running time as Lithium cells (but are cheaper per cell and can be recharged about a 1000 times).
The main down side of this particular light is that once the battery power is used up it just cuts off. There is no dimming or warning, it just stops! This can be worrying if you are doing 20mph downhill at the time. Actually it is not that bad. If you are going downhill you will be in one of the higher light settings. When the batteries cannot cope with the power output the light does stop but if you click the button it will restart on a lower setting. So a moment of literal blind panic and then enough light to see and slow down by. To avoid this though it is best to change to a fresh set of batteries before the current set are to expire. Two sets will get me through a [summer] night. Click on the image below for more product information from Amazon.
Timing your trip will help on your lights strategy. If you go at the end of June you will get about 16-17 hours of daylight to play with. If you try in December it will be more like 8 hours (or less in Scotland).
Do I need to take lights?
You should take emergency ‘be seen’ bike lights.
If you are planning long days in the saddle you should carry main lights in case you are delayed and have to finish in the dark.
If you are camping you could carry main lights that will double as camping lights.
If you are planning your trip in months of shorter daylight hours you should carry lights. The light levels at the beginning and end of these days can be particularly poor, especially if raining.
I took my Knog frogs and a Cateye TL-LD610 main rear light to make sure I could be seen from behind.