20) In a high pressure mercury lamp, to vaporize all the mercury and for the lamp to reach full brilliance, it requires :

21) The rating of I.C.D.P. switch used in a neon-sign tube should be :

22) H.P.M.V lamp gives :

23) If on removing a defective starter, the fluorescent tube lights up, the fault lies in the :

24) A separate starter and socket is required for a fluorescent lamp. What is it called as ?