You could fit a set of very low profile driving lights or DRL style led strips just under the bumper. At night they'd throw plenty of light and not look too bad if they were tucked right under the bumper.
You could go for a pair of flush mounted/recessed lights each side of the number plate?
The only way you'll get a lot of light for actual reversing in the dark from the single bulb supplied is to do some pretty heavy custom work to that lamp, maybe try and get a headlight bulb mount and fitment in there. Tricky but any things possible.