Back to basics – Let there be light

I’m a huge fan of cycling in the dark, which is just as well, as almost half the year most cycle commuters cycle in the dark both ways. There’s something completely different about cycling in your personal bubble of light, along otherwise totally dark roads, and I rather strongly feel this is something everyone should try, perhaps by signing up to ride the Dunwich Dynamo, or the Exmouth Exodus.

Obviously, night-time cycling requires lights, and lights are split into two different categories: lights that allow you to be seen by other traffic, and lights that allow you to see where you’re going.

Lights  to  be  seen

If you’re going to only be cycling on lit urban roads, then all you need are lights that allow other road users to see you.  Aside from being a legal requirement, there is a safety element to this.  Because of that, I suggest you go for lights as bright as you can afford, and avoid the pound shop blinkie lights.Remember, the purpose of your lights is for you to be seen, so you yourself a favour and test them. Lock your bike – with lights on – then walk some 200 metres away. How bright is your tail-light now?
Also consider LED ankle straps, which (if you’re cycling in normal clothes) can double to keep your trousers away from the chain.

Lights  to  see  with

We are immediately looking at better and brighter lights here. When talking of brighter, it would help if we had a system to measure light. As it happens, there are several: some lights are rated in Watts, though that’s becoming less common now. Most bike lights are rated in lumen, while dynamo lights are rated in lux. All of which makes it rather difficult to compare apples with apples.
Most bicycle lights are powered by batteries, but some are powered by a dynamo. Let’s look at battery lights first, and the first thing you need to do is figure out how long the batteries should last. If yours is a 30-minute each way commute, then you don’t need lights that will last many hours. If, however, you’re planning on riding an all-night bike ride, like the Dunwich Dynamo, then your battery needs will be substantially different.

A word of caution: most battery lights have claims of brightness and battery life that differs from reality, and just because the ad said the lights will last for six hours on a single charge doesn’t mean that’s the reality. Always test lights when you get them, to see how long they’d last.

Your riding style will heavily impact on your choice of lights. If you’re planning on tearing down red-rated MTB tracks in the dead of night you will need a lot more light than when you’ll only be riding on tar. Also – and this is important – you must consider others. Those off-road lights should never be used on the road, or on paths shared with others, as they flood everything ahead of you with light, blinding oncoming traffic.

The  tech

Let’s have a quick look at the technical bits, shall we? Batteries are rated in mAh (milli-Ampere per hour, or just milli-amp/hour). This tells you how much current the battery can supply, and using this, we can calculate how long the battery should last, when we know the current requirements of the light itself. No, you don’t need to do complex calculations – simply bear in mind that mAh is a useful rating, with a higher rating meaning longer battery life.

Next, we do need to divert briefly into the wonders of Lithium-Ion (Li-ion) batteries. You also get Li-Po (Lithium-Polymer) batteries, and many believe these are different to Li-ion batteries. Li-Po batteries are still Li-ion batteries, but they use a polymer internally. For practical purposes, we’ll all treat them the same.
Li-ion batteries are wonders of the modern world, but they have explicit limits, and you need to understand these limits. For starters, regardless of the overall voltage rating of your battery pack, the internal Li-ion cells are 3.65V. You might be extremely hesitant to happily carry a mobile phone in your pocket if you understood just how unstable Li-ion batteries can be!

They are safe to use within well-known limits, and these are important. For starters, a Li-ion cell should never drop below 3V, and never be charged above 4.2V. If the internal charge drops below 3V, copper dendrites forms, which can degrade the performance of the cell, or short-circuit it. If the internal voltage goes above 4.2V, lithium dendrites form, which will cause the cell to short-circuit. Now for the fun bit: a Li-ion cell that’s short-circuited will rapidly heat up, and especially when overcharged, may start burning, or exploding. To guard against this, battery packs have built-in protection to measure internal voltages across all the cells in the battery. If any cell drops below or rises above the safe limits, the circuitry will prevent the entire battery from working, and it would appear to be a dead battery. This is an essential safety feature!

Li-ion batteries can be used to power things in environments where the temperature is between -20 degrees Celsius, and 60 degrees Celsius. Charging these batteries, however, have different limits: never charge a Li-ion battery when the environment it is in is below zero degrees, and take great care when the temperature is between zero to 5 degrees Celsius. Never charge a Li-ion battery if the environment is hotter than 45 degrees Celsius. As an aside, you can immediately see the problem with electric cars and a warming planet, can’t you? Remember, the temperature inside a car rapidly gets very hot on a summer’s day, and can very easily exceed 45 degrees.

Li-ion batteries do not cope well with rough treatment, and banging them about can cause internal short circuits, again leading to fires or explosions.

Also, if you’re thinking of winter adventures, your lights’ batteries, as well as that of your phone, and your cycle computer, are impacted by these limits, and you should pay attention. Yes, that includes when recharging gadgets from a power bank!
Your gadgets lie to you: their batteries are never 100% charged. A fully-charged Li-ion battery has a charge of 3.6V across each of the internal cells that make up the battery. The charge can go higher, but that’s risky, so gadgets will pretend that’s 100% charged.

Finally, especially when buying cheap battery lights off Ebay, do yourself the very solid favour of getting a sizeable metal tin to place the battery pack in before you start charging it, and never leave it on charge unsupervised, especially not overnight. It’s unlikely that the battery will start burning, but it it does, you want to have it contained! In the very unlikely event of a battery fire, remember that Lithium reacts with water, so never to to extinguish a battery fire with water, as that can make things far worse.

Now I’ve scared you enough to respect Li-ion batteries, lets have a look at the lights themselves. Most battery lights produce light using technology from a company called Cree. Cree make LED (Light Emitting Diode) chips, with the most common chips being XM-L Tx chips. The T-number refers to lumen output of the chips.

Especially when buying off Ebay, you will see lights with ludicrously high claimed lumens ratings. I’ve seen T6 lights where the seller claims 2 500 lumen, which is as likely as a formation of pigs flying over your head right now. T6 chips typically output anything between 700 and 1 400 lumens. Don’t get excited about the 1 400 lumens – your single Cree T6 light will never produce that, unless it has world-class driver technology, and a huge heat sink, together with a battery pack that’s actively thermally managed. Just do yourself a favour and treat it as if a T6 chip produced 700 lumen.

You get what you pay for, right? Well, often you don’t. See, you can buy two zoomable (an important feature that I’ll cover in a bit) Cree T6 “tactical” torches, each powered from a single 18650 Li-ion cell (wrongly called a battery by most people) for around £10 (or less!) each. For years I commuted daily using exactly that setup, with 8 miles of my commute along otherwise pitch-dark rural lanes.
Equally, you can spend upwards of £200 for a battery light that uses a single T6 chip, producing just as much light, and powered by a single 18650 cell. I know which option I’d go for every time!

Why zoomable? Being able to zoom the torch (for that’s what it is) means you can absolutely control the cone of light. I used to ride with two such torches, with one zoomed to flood the road immediately ahead with light, while the other zoomed to light much further ahead. That worked very well for many years, and if I had to go back to battery lights, I’d do the same again.

You can now buy cheap monster lights, made with nine T6 chips. That’s a minimum of 6 300 lumen, which is a huge amount of light! That would be OK on those MTB trails, but please don’t ever use something like that on the roads? Besides, as those lights (like almost all battery lights) scatter the light everywhere, lighting up the road, the hedges to either side and the trees above, you will get a great deal of light reflected back at you, and I guarantee that will ruin your night vision. Along with blinding any oncoming traffic, that’s a recipe for disaster!

The country with the most stringent bicycle light laws in the world is Germany, and that has the benefit of making German dynamo lights the very best that money can buy. Dynamo lights have the benefit of always being available – as soon as the front wheel (containing a hub dynamo) starts turning, your lights are on, but not all dynamo lights are equal. Also, dynamo lights produce less light than battery lights, so it seems counter-intuitive to change to dynamo lights. I certainly was extremely sceptical, until one year, while cycling an all-night bike ride called the Exmouth Exodus (from Bath to Exmouth, though the night) and I cycled with another rider who was using dynamo lights.

You see, dynamo lights use the light far better, and focus the light just where it’s needed. They don’t waste the light by scattering it everywhere, and when correctly set up won’t blind oncoming traffic. To me it’s a no-brainer, and upgrading to dynamo lights was the best thing I’ve ever done to my bike. No more hassles with charging batteries, and no more worries about whether or not my battery pack will last the duration of the ride.

2 thoughts on “Back to basics – Let there be light”

  1. I have a tandem with a bottle dynamo and a conventional front light. I have not used it much at night for many years and have used conventional lights as a supplement, now thinking of upgrading lights. Are there tandem suitable dynamo hubs or should I just upgrade to a better bottle dynamo when I switch to LED lights?

    • Hi Stephen,
      I would suggest you either rebuild the front wheel around a hub dynamo, or buy a ready-made dynamo-hub front wheel. Dynamo hubs are more efficient that bottle dynamos, and they’re silent.
      Of course, unlike a bottle dynamo, you cannot stop the dynamo turning when the wheels are turning, and some are concerned about that. You will not be able to feel the difference in drag caused by a hub-dynamo, and over 100 miles, it may slow you by up to 5 minutes.
      Over that distance, plenty of other things – including my habit to regularly stop to take photos – will slow me by much more, and I can happily live with such a tiny delay.


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