NBN EN 15220-1:2009

This European Standard specifies the requirements for the design, dimensions, performance and testing of single/double brake indicators with or without electrical contacts. It applies to pneumatically operated brake indicators visible from the outside of the vehicle.
NOTE Brake indicators are for giving precise and accurate information about release and application of the brake.
This European Standard applies to brake indicators on railway vehicles used on the main national networks, urban networks, underground railways, trams and private networks (regional railways, company railways etc.).