The Oldham Cap Lamp and Battery introduced in the 1940s
"At my first pit the lamp bezel had different colours. So white was BACM (British Association of Colliery Management), Blue was COSA (Colliery Officials Supervisors Association), Yellow for NACODS (National Association of Colliery Overmen and Deputies) and black for NUM (National Union of Mineworkers)." (Adrian Brant)