Member States shall take the measures necessary to ensure that:
(a) normal hours of work for night workers do not exceed an average of eight hours in any 24-hour period;
(b) night workers whose work involves special hazards or heavy physical or mental strain do not work more than eight hours in any period of 24 hours during which they perform night work.
For the purposes of point (b), work involving special hazards or heavy physical or mental strain shall be defined by national legislation and/or practice or by collective agreements or agreements concluded between the two sides of industry, taking account of the specific effects and hazards of night work.