T5 lamps are very active. They actually take about 100 hours to fully energise. Over this period the lamps light output increases by around 30% as of course do the UVB wavelengths,
They also take about 5 mins each day after that to properly energise.
For a med species and with a suitably reflected lamp, the upper index basking zone, that is where the distance between the lamp and the top of the shell is at it's shortest it is indeed 12-15"
Remember to provide good space for light and shade. Then the little chap can properly self regulate it's own level of exposure at it has need.
John
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