Price of 24 hour lighting is about £1 - £2 per watt year (standard overhead fluorescents). For typical office building lighting intensity, that's around £15 - £

Price of 24 hour lighting is about £1 - £2 per watt year (standard overhead fluorescents). For typical office building lighting intensity, that's around £15 - £50 per m^3. Assuming the high end of that scale, for the building you mentioned, the yearly lighting bill would be £5 million.