I get about 3 hours on one of the standard cheap Chinese lights, and they are plenty of light for me at 30 MPH. Can't say I go 40 very often. My favorite is to get one of the single beam lights with a smooth reflector (this will be pretty spotty rather than flood) and then put on a beam widener from Action LED Lights.

Sample of the light I'm talking about: 1200LM Lumens CREE XM-L T6 LED Bicycle Light Torch Bike Headlamp Headlight | eBay
Lens: Wide angle lens for Cree XML T6 Bike Headlight, bicycle light, includes O-Ring | eBay

I've not had a problem with the lights (I think I own 3 or 4 now) but the batteries are usually not great. I get 3 hours on high when they're new but they degrade quickly. Therefore I like to get a case like this:

4 x 18650 Battery Pack Waterproof Storage Case Cover For Bicycle Bike Lamp USA | eBay

Then buy four good (Panasonic or similar) unprotected cells from Amazon (about $25). Buy the light with the cheap battery and charger, and keep the battery charged and ready in your bag as a spare.

All in you're looking at $50 or so.

On the back, I like the Blitzu Cyborg 168T, but another option is the MagicShine, which runs off the same pack as the headlight:

MagicShine MJ-818 3W LED Tail Light head with Y-cable & O-rings | eBay

Or you can use that battery that came with the light to run this. I kind of prefer to have them both on the same battery so I KNOW when the taillight goes out, because the headlight does too.

I also consider it essential to run TWO taillights, because if a taillight fails, you may not know it. Also have some reflective stuff in the back.