A system, method, and computer program product for communicating with an LDAP server. The first and second external electrodes are provided on a first principal surface. The tests allow to anticipate and hence prevent hazardous opening of barriers due to a faulty zero speed indication. The deuterium lamp can be inserted into and removed from the lamp box from thereabove, so that lamp replacement becomes easier even when the housing is made compact, whereby the light source apparatus can be carried easier outdoors and in the field.