Dinotte makes a light that is only for daytime use it is so bright they make you check a box making sure you understand it is for daytime use only, this is not that light but I have heard is quite bright and has a lot of mounting options:
https://store.dinottelighting.com/ne...tery-p111.aspx
My go to would be the Big Cobber from Knog but I don't know it would work in your mounting situation though probably would easily mount to the seat tube as you have space but you would have to give it a go. It is a very bright one as well.