It is primarily to support the head light in these conditions that you look for an auxiliary light or two to gain more vision after dark. And just like having the headlight on makes your more visible, having auxiliary lights running in the day makes your motorcycle stand out and has a positive safety implication. Human drivers tend to not crash into things they can see.
Here's a quick primer on how these lights work, what they're for and how to find the one you like.
Not every rider needs them. If you ride a lot within the city, mostly in daylight, you don't need them. Extra lights serve a purpose though. The shallowest of them is the look of the bike. Adding these to a gigantic adventure tourer does look good - and there is always the danger that you will overdo it.
But the real purpose to fill in the gaps that your OEM headlight leaves and have a backup source of illumination. Both of these apply more to the big distance rider and adventurer than almost any other kind of rider.
The second is easy to understand. LED headlights rarely fail. But bulb-type headlights are more fragile, although the failure rates today are very low. And in that event, a second set of lights might be enough to get you home.
The real reason is to complement and supplement the headlight. For example, if you ride in off-road terrain a lot, especially early in the morning, you might want more light near the bike at the front and on the sides so you can see more and ride better. Or if you, like me, like to cover substantial distances in the quiet of the pre-dawn dark, you might want powerful lights that reach further than the headlight can so that your mile-munching happens with confidence and clear vision.
There are two reasons. First is the law. Headlights and all forward illumination are tightly controlled by regulations. This is because they are the most powerful lights on the vehicle and they can easily blind oncoming traffic which is more than an annoyance, it's actually dangerous. Aftermarket and auxiliary lights are usually marked as "for off-road use only" which means they don't follow the laws.
Second is the cost. You wouldn't accept a Rs 30,000 LED headlight on a Rs 2.7 lakh KTM 390 Duke if it were OEM equipment. The law-abiding halogen headlight is very cheap and in proportion to the cost of the motorcycle. When it comes to adding the lights though, your budgeting may or may not be in proportion to the cost of the motorcycle.
In general, the lights are classified into four classes. Floods, spots, hyperspots and hybrids. These classifications are based on the sort of light pattern they produce. Which also tells you what they're meant to do.
Hyperspot
The hyperspot is the specialist among the auxiliary lights. It casts a very narrow beam, you'll read a figure like 5° or 6° as the light beam description. At close range, like if you point it at a wall, you will see an extremely bright and well-defined circular light beam. The narrow beam projects light over huge distances. A 3,000-3,500 lumen beam will usually carry a 1 lux distance of 600m or greater. The truly impressive ones can usually hit 900-1,000m. These beams are excellent for high-speed highway work when you'd like early warnings of what's ahead. Usually, a hyperspot is the last light you get. This is because the specialised nature of the light beam means it doesn't light up anything else except whatever is in front of the light. Focusing a hyperspot is critical, from the illumination perspective as well as in terms of the risk of dazzling oncoming traffic.
Spot Beam
The Spot beam is a great source of confidence for the rider. It projects a 10-15° beam that shoots out over a good distance and isn't too narrow like the hyperspot. There's a well-defined circle of light but it's a notably bigger circle than the hyperspot and it reaches a little less into the ether. A 3,000-lumen spot beam can easily hit 3-400m. The wider circle of light, once again, means focussing the spot beam is important to its utility and you have to careful not to dazzle oncoming traffic. Most focussing instructions suggest choosing to align the hotspots of the beam exactly aligned with the motorcycle but dipping so that at 100ft, the beam dips 2 inches or 5cm in height from the center of the light.
Flood Beam
As the name suggests, a flood beam projects a an extremely large circle of light ahead of the light unit. This is good for filling in the gaps that the low beam of the motorcycle might have. Floodlights can be extremely bright and they project really wide light beams, you will see numbers like 80° or 120°. Focussing a flood beam is about minimising dazzle for oncoming traffic because the wide nature of the beam means exact light unit focus isn't crucial to the operation.
Hybrid Or Driving Light Patterns
A hybrid or driving pattern usually uses multiple LEDs set up with a combination of spot and flood lenses to produce a beam that balances the distance of the beam and the width of the beam. These are perhaps the most useful of the lights to add to a motorcycle with weak headlights because their job is to produce a reasonably wide beam with a significant distance. Some of the smarter lights will give you the option to change the lenses so that you can choose how many forward pointing LED units are working as floods or spots depending on how you'd like to help the motorcycle headlight.
