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Life of Neon Lamps
As previously stated in the 'Operation' section, neon lamps do not experience catastrophic failures in normal use.
Life of neon's is typically quoted as a reduction of light output of 50% from the initial level when operated from an ac supply and within their stated design currents.
The reason for quoting general lifetimes with ac supplies is due to the fact that the sputtering effect (section 4) is made worse with dc supplies, since one electrode is always acting as the cathode and thus wears at a faster rate. Neon's operated with dc supplies will have approximately 60% of the lifetime figure quoted for ac.
The good news is that life expectancy increases considerably as the operating current is decreased.
Mathematically the life versus the operating current follows a 3.3 power law, such that the theoretical life can be calculated from:
Le = Ld(Id/Ie)3.3 OR Le = Ld(Re/Rd)3.3
Where Le is the estimated life at new current Ie and resistor Re.
Ld is the life given by manufacturer at the design current Id and series resistor Rd. The graph below shows the theoretical life for a T16/30HB Timelamp neon.
Nominal operating current for this is given as 1.5mA with a life of 25,000Hrs. Reducing the current by just 0.2mA to 1.3mA has theoretically increased the life to 40,000Hrs.
The relationship which is expressed in the above graph and equations should not be used as an absolute rule for design but rather as a guide to the effects of changes in operating current.
Other factors, such as temperature and the effects of strike voltage with time need to be considered.
What is a Neon Lamp - Features - Applications - Operation - Electrical Characteristics - Life
