Variable brightness emergency lighting - has initial high level intensity after mains failure and reduces to normal level

摘要

An emergency lighting incorporates a luminous flux control. On failure of the mains v oltage supply a lighting system is automatically powered by a storage battery. It is of the type used for stage lighting in theatres, in industry etc. The emergency lighting level is set to a magnitude. At least 5 Lux in general is necessary for theatre lighting back-up systems, with industrial systems requiring a magnitude some 10% of the normal lighting intensity level. Immediately following the mains failure, the emergency lighting is supplied at an increased lighting level via a time control for a predetermined time. Subsequently, the emergency lighting automatically switches over to the nominal intensity corresp. to the design of battery and relative to the nominal lighting time.