a 30 hz frequency since uv light produces by activated hg ions in the plasma of the arc may be absorbed if the uv quanta encounter ground state atoms a portion of the uv quanta does not reach and activate phosphor to produce visible light the probability is increased the greater the distance the uv quanta must traverse to reach the phosphor for this reason light output is increased when the current is forced to flow close to the phosphored surface however uv quanta emitted in the reverse direction have a reduced likelihood of reaching the far wall and being converted to visible light to product more light from a larger phosphored area the lamp diameter is increased beyond the conventional t 12 lamp size a 38 mm 1 5 34 diameter to convert more uv quanta to visible light an internal cylindrical structure 12 having an exterior phosphored surface is placed coaxially in the lamp envelope 13 as shown in fig3 the coil 14 and 15 similar to coils 2 and 3 producing the rotating magnetic field constrain the arc to rotate close to the phosphored surface of the lamp envelope 13 and around and close to the phosphored surface of the inner structure 12 the inner structure is supported by three legs 16 at each end as.