The Road Vehicles Lighting Regulations require vehicles first used on or after 1st April 1986 to be fitted only with lamps and light sources that have been approved to established standards, which govern luminous flux, colour and dimensions. The regulations also require vehicle owners to replace light sources with like-for-like approved replacements and ensure that the lamps fitted to their vehicles do not cause undue dazzle or discomfort to other road users. The Automotive Market Surveillance Unit (MSU), based in the Driver and Vehicles Standards Agency, is responsible for ensuring that vehicle products comply with legal standards and are sold for correct usage. If the MSU discovers evidence of non-compliance in a sector of the market, investigators will take action. This includes warning and potentially prosecuting any company involved in illegal activity.