Best Front/Back lights to buy

Garmin Varia should be considered separately, as it's really a unique product range. Some people swear by it, but if you just want a light then you're paying a lot more for features that you won't use.

There are lots of good options out there. It depends a bit on your budget and use-case. If you're riding through the night on unlit roads, you probably want something a bit different than if you just want it for a couple of hours on city/suburban roads.

I currently use Exposure lights (Sirius front, TraceR rear) and they are good. They certainly feel very high quality and I have had no problems so far. However, they are expensive! Furthermore, the Sirius is probably the minimum brightness I would want for night riding on unlit roads, and doesn't have a massive runtime on high brightness levels. So for regular, long night rides, I would look for something with longer runtimes, and maybe a slightly higher output. No complaints with the TraceR, beyond it seems to have quite a narrow beam where the majority of the light is directed.

I also own a couple of small Lezyne lights which I used on my town bike for several years, again very happily. The ones I have (Zecto) are probable not suited for your use case, but as an indiation of Lezyne's quality I had zero problems despite daily use in all weathers.

Maybe say what bike he rides - those riding similar machines might be of a like mind when choosing what to attach to it! Also up to how long are his longest rides (time)? And does he need a light to see where he's going, or just to be seen? And is he a sucker for tech stuff, like a light that responds to the ambient brightness or deceleration, or does he prefer straightforward and simple?

Because there are a gazillion lights to choose from, and how do you decide? For example, I'm holding out until they start using USB-C charging ports instead of the irritating, annoying legacy micro-usb. But that's me!

I have a Cateye Ampp 800 on the front and a Moon Nebula on the rear if that's any help.

Also a Topside front/rear helmet light.

How thoughtful! There are so many good inexpensive lights available now, it's hard to go wrong, at least functionally speaking. Consider whether he would prefer a powerful front light to light up the road (which will be a bit heavier), or something to be seen by (or even both). I alternate front lights, only fitting a powerful one when I know I'll be riding in full darkness.

As these are a gift, maybe consider also the slightly nicer (more expensive!) lights. I think Knog rear lights are a cut above most others in terms of design and aesthetics, and Exposure's are very well made, all anodised aluminium which gets bikies excited, and as far as I know, work very well. Cateye's and so on work great, but are a bit more pedestrian looking. 

Als maybe surreptitiosly check if he uses a garmin or wahoo computer, and how it mounts to the bars. It's quite possible there is a GoPro mount underneath it which some lights can attach to, keeping everything very neat.

Front: I have a Lezyne 800xl that I'm very happy with. Good beam spread, good run time, handlebar mount is a thick rubber band and it seems well put together. Charge via micro-USB socket on the back. It recently scored top in a Cycling Weekly guide FWIW.

Rear: I really like Cateye's rear lights. Their Rapid X series are very slim and lightweight and are USB rechargeable, they fit via a rubber band and seem like a very good option. I use a Lezyne Micro Drive, it's a cylindrical shape and is bright enough but if I was buying again now I'd get something with greater surface area  like a Cateye Rapid X3 or Lezyne Zecto.

Have you checked the road.cc reviews? Under Accessories, there are sections for front, rear and sets/pairs (F&R).