veganbikes

As often as needed. Cheap lights are generally not worth it except for a child's bike not being ridden at night. You want something bright with a good beam pattern and ideally a good long battery life (unless really good about charging) I also recommend more simple setting light too many front lights these day have unneeded flash modes and strobe modes for your discotheque parties which are just not needed while riding a bicycle amongst others. Ideally the rear would be solid as well but red light is a bit less damaging to the eyes at night but I would rather have light all the time and something like the Lezyne or Krypto lights that have an accelerometer so they do get brighter when you stop like other vehicular traffic.

However if you get a dynamo system there is no charging needed, all you have to do is ride your bike and you generate the power for the light and many of the dynamo lights out there have excellent beam patterns usually to STvZO standards (which are irrelevant as law in the U.S. but really useful for what that law requires of the lights for being around other road or trail users) plus you can even get some with those brake lights as well and now Supernova has one with a high beam. It is more costly yes but never having to worry about charging and always having light day or night without worrying about turning things on or off is pretty nice.