This is another one of those situations where the 'law' is given as guidance to the Local Authorities and it is their responsibility to assess whether anyone is guilty of light pollution - which is the issue.Hi - I've bought a 150W floodlight with PIR sensor. I'm potentially not allowed this??
Some councils suggest 200w (Gravesham) per light some suggest 120w (Sefton).
Others work to a lumens scale because a 10w LED floodlight can be just as a much of a pain as a halogen rated at 120w.
Most say that the lighting power/lumens value is less of an issue where properly functioning PIR's are in place - nearly all say it is better to fit bulkhead style lights around your house rather than floodlights.
The only true to answer to your question is to speak to your Local Authority and seek their views.