Half the amount of Lights for Sky Tubes

In our office it’s not too dark with the lights off but if we replace half of the light fittings with sky tubes it would be bright enough. The costs of saving of only having to fit half the light fitting would pay for the Sky Tubes at the point of install, sono waiting years to get your money back.The electric bill would be cut back too with only half the lights been used. We have about 20 x 180 watt light fittings so it’s like boiling a kettle or 2 all day.Replace half of them or more and the savings would be huge.