Light itself, and minor domestic light fittings, are not subject to planning controls.
Nevertheless, if you are planning to install external lighting for security or other purposes, you should ensure that the intensity and direction of light does not disturb others. Many people suffer extreme disturbance due to excessive or poorly-designed lighting.
Ensure that beams are not pointed directly at windows of other houses. Security lights fitted with passive infra-red detectors (PIRs) and/or timing devices should be adjusted so that they minimise nuisance to neighbours and are set so that they are not triggered by traffic or pedestrians passing outside your property.
A neighbour might take you to court if you are negligent or cause nuisance.
If your property is a listed building you should always consult the local planning authority.
Disclaimer - Wales
This is an introductory guide and is not a definitive source of legal information. This guidance relates to the planning regime for Wales. Policy in England may differ. If in doubt contact your Local Planning Authority.