For a tubelight, a mount for a headlamp can work. Just drill some mounting holes through the base. Or use stickytape, ’though that disintegrates over time.
Czech out posts like this: [Review] 77 Outdoors D25 Headlamp (18650) - #178 by alpg88 , as you can do something similar if you got a 3d printer, or a$k if someone could throw together something with the right dimensions if you need something made-to-fit.