Zones and IP ratings in plain English
Bathrooms are divided into zones based on proximity to water, and fittings must carry an ingress protection rating suitable for the zone they sit in. Inside a shower enclosure the requirement is strictest; further from water it relaxes.
The practical point for homeowners is simple: a fitting is not suitable just because it is sold as a bathroom light. Its rating must match its position.
Layer the lighting instead of using one ceiling light
Three layers work: general light for the whole room, task light at the mirror at face height rather than overhead, and low-level or accent light for evening use.
A single central downlight array produces shadows exactly where you need to see - under the chin and eyes at the mirror. Mirror-level or mirror-integrated lighting fixes that for very little money.
Switching, mirrors and shaver points
Standard switches are not permitted inside a bathroom - pull cords or switching outside the door are used instead. Shaver sockets must be the isolating type and positioned away from direct spray.
Heated or demisting mirrors need a fused supply planned at first fix. Deciding on the mirror after the walls are tiled is a common and avoidable regret.
Certification you should receive
Electrical work in a bathroom needs to be carried out by a competent person and certified appropriately. You should end the job holding certification for the work - it matters for insurance and for future sale, and it is the standard evidence that the installation was tested.