If you are riding at night, or potentially riding at night, you will need lights.
Serves 2 purposes
Illuminates road/path ahead of you
Helps cars and other bikes see you
Urban Riding
Daytime
You want a specially designed light that is bright enough to be seen in the daytime
Nighttime
Lights help you see the road in front of you, but more importantly make is easier for cars to see you
You don't need the brightest, most expensive lighting system
Gravel Biking and Mountain Biking at Night
Lights made for urban use leave much to be desired
You will want a much brighter light to illuminate the trail
Lights can get pretty expensive and you'll need to consider how much light do you really need (as opposed to want)
Examples of Urban Riding Lights
Trek/Bontrager Ion 200 RT / Flare RT Light Set
Brightest daylight available
Front/Rear set
Expensive but worth the cost if you are doing a lot of road riding
Knog Plus
Affordable daytime light
Can get front/rear kit
NiteRider Swift 300
Economy night option
Bright enough for urban areas at night
Cateye AMPP900
Economy night option
Bright enough for urban areas at night
Amazon Economy Light
Front/Rear Set
Most bang for the buck!
Not so bright rear light
Required for night riding on roads
Ideally, get one that not only blinks, but doesn't consistently blink as the same interval
A blinking light is more noticeable than a solid light
A light that blinks at different intervals is more noticeable than one that blinks as the same interval over and over
Some rear lights work as brake lights
Some rears light auto dim when other bikes are behind you
A few lights have radar to alert you a car is approaching
Examples
Trek/Bontrager Ion 200 RT / Flare RT Light Set
Brightest daylight available
Front/Rear set
Expensive
Knog Plus
Affordable daytime light
Can get front/rear kit
Amazon Special
Reasonable brightness
Good Value
Fenix BC05R Taillight
Economy option
Battery drains when not in use
Exposure Boost-R + ReAKT & Peloton
Auto dims when you ride in front of another rider
NOT Recommending for Scouting
Complex
Expensive
Soon to be outdated?
Specialized generator hubs able to power low wattage devices
They power on as you pedal the bike
5mph can power a dim light
9-13mph to reach full brightness
Still not as bright as a quality battery powered lights
Useless at slow speeds
Not able to keep up with power of high watt devices, such as cellphone, while they are running
Read more at bikepacking.com/plan/dynamo-hubs-lighting-charging-guide