This is a situation where your college learning always lets you down as its an area not explained deep enough which i think should be, we can safely say that a single 70w flourescent has an inrush to be taken into consideration but been on its own on a 6amp or 10amp mcb its too small to be of concern, the problem arises when you have multiples of fitting with all their accumilative inrush currents as you basic load calcs to mcb size simply no longer are effective, consider 14 X 58watt single fittings which will work out at approx 3.5amps.... so by your basic teachings you would fit a 6amp mcb type b or c but then applying the 1.8 factor pushes us to 6.3amps thus a 10amp is needed after working this out the last step would be to reference technical data on the mcb with manufacturer (merlin gerin in this example) the maximum no' of 58 watt fitting on a 6amp mcb is noted as 13 so clearly a 6amp mcb is too small, using the inductive factor of 1.8 should normally get you the correct size mcb but occasionally it dosnt, unfortunately it dosnt go higher than 58watts in the tech notes so i cant give you a definitive answer but my rule of thumb is double the load instead of applying 1.8factor and then see what mcb you need and in your case a 10amp should be ok so i suspect a problematic ballast or a type c mcb may cure it, when designing circuits with accumulative inductive loads you need to reference the mcb limits for your lighting before you decide how many per circuit, the above example is for 58w flourescents only and results vary with different lamp types and also with mcb brand so always refer to tech' tables or call them if designing such circuit or it can be an expensive error.
The 1.8 factor is usually good for standard flourescents and working out mcb's but when you drop onto metal hallides and high pressure mercury vapour then the 1.8 factor developes cracks thus refering to manufacturing data is a must, and this applies to all inductive loads like motors, transformers etc
