When you turn off your traditional light switch it should isolate the power meaning no current gets through to the lamp and it remains off. If there is an afterglow and the lamp remains on this may indicate the switch is still letting current through to the lamp. We would recommend consulting a qualified or competent person to test the switch and proceed accordingly.
In some instances modern electronic controllers/switches/dimmers can cause this phenomenon. If you are experiencing this please check you are using a compatible controller by referring to the following link: https://www.megamanuk.com/products/dimming-compatibility/
If the problem persists then please contact our office, who will be happy to assist 01707 386 000.