The loupe I use (looks like this) has LEDs, which work well for that.

I tried one of those too, could never get it to focus while keeping it in place. I also tried using a USB microscope (I already had one), same problem. I've had the best luck with this $7 30x/60x loupe. The 30x lens is sometimes good enough, and when it isn't, it's got a fairly wide focus and helps to find places to check with the 60x.

I use this 30x/60x loupe. I've tried using both a USB microscopes and a "pocket microscope" but found both really hard to focus on a live plant without moving it from the spot I was trying to check. With the loupe, the wider 30x view sometimes good enough, and when not it helps to find places to check with the narrower 60x.

I like this $6 loupe, which has both a fairly wide 30x lens and a narrower 60x lens. I've tried USB microscopes and handheld microscopes, but found both really hard to focus on buds unless I cut them off and hold them steady.