I rode with a guy this weekend who uses the L&M Viis 360+ light. It's effective but at MSRP $150 it is not cheap. He's a retired cardiologist so money is no object. It will last at least 8 hours on flashing mode but a lot less on steady.

In contrast I rode with flashing lights front and rear which together cost a bit over $10. Both are USB rechargeable. The front one has a 650 mAh internal battery and the rear 500 mAh so are good enough for a couple hour ride before petering out. The 100 lumen rear is a bit lower in lumens than the L&M on flashing mode (100 vs 125). The front one is similar to the Zekto Drive 100 lumen light - same LEDs and similar case. BTW, L&M leaves you completely in the dark when it comes to battery size for USB lights.

If you don't mind looking a bit dorky, there are some who have posted pictures of a helmet mounted XML-T6 flashlight. The advantage is you choose the battery instead of guessing what the heck the company put inside it. The ones I bought most recently weigh 145 grams (5.7 oz) and with a Panasonic 18650 battery 190 g (7.5 oz). You would get your 800 lumens with the T-6 bin. The flashlights are sub $10 too.