I receive pop up adverts daily from bike shops informing me of their latest sale. Usually groupsets or brakes going at a great price, or shoes and clothing going out of season. What I rarely see are lights or lightsets.
I never used to ride during the day with lights on (unless visibility was poor ). Now I don't ride without them. It shouldn't be necessary but for the price of some AAA batteries I want to be as visible as possible ( I also now wear a hi vis vest , so I resemble a lollypop from a distance).
On week days I commute by car, and on overcast mornings often see ( just as I'm around 30 yards away) cyclists without lights looming out of the fog. If cars need lights on to be seen then surely a bike, a tenth of the size needs them.
We don't need an MOT, road tax/ emissions tax ( zero emissions, same as electric cars ), insurance or even a helmet, though a helmet is advisable, to ride on public roads. What we do need to be legal are working lights front & rear. Available from pound shops, bike shops, supermarkets even eBay and Amazon ( often next day ), there's really no reason not to have some.
Cheap lights are better than none, but won't illuminate the road ahead, highlighting potential hazards. More expensive lights project a beam and are more visible in otherwise unlit areas eg country roads or cycle paths. Either way always check that the batteries have sufficient power to complete the journey. I have a smaller back up set fitted in case the main set fails.
USB rechargeable lights that plug into your ebike battery, or work computer mean you have enough power to light your way home. Some ebikes have lights built into the battery to save space. Others, mostly in Europe, use a dynamo system powered by the front wheel. Helmet manufacturers are now integrating lights in the rear to make road users aware of the riders presence.
As a wise man once said " Let's be careful out there".