If you fancy an upgrade, it's the same common number plate light that's used on the Berlingo and countless other Peugeot/Citroen models, 6340F0. You can search for this part no on ebay or whatever There's a commonly available Chinese replacement for the entire unit with LED lights sealed inside a waterproof unit. The original just pops out, swap the connector over and clip in, it's probably easier than changing the bulb.
I'd previously tried LED bulbs inside the original unit on the Berlingo but they kept expiring, presumably due to the heat from them being on for a long time in such a confined space. I've had the LED sealed units on my Berlingo for lots of years and they're still great. Much nicer, brighter and crisper than light bulbs, they kind of serve as a secondary back light. I've had no issues with MOTs either. They'd probably also provide some good illumination for the reversing camera on the DS5 too. One example unit among many...
https://www.ebay.co.uk/itm/125030684916