A typical LED tube uses less that half the energy at 24 watts versus the fluorescent 58 watt tube with the fluorescent fitting also utilizing a ballast which eats up another few watts for good measure. Less than half the energy means less than half the running costs. That means a considerable reduction in carbon output too.
Example: replacing 60 fluorescent tubes running 9 hours a day with LED would see a return on investment at the beginning of year two, yielding a saving of over €4200 at the end of 5 years. This does not include the cost of getting maintenance to come and change each fluorescent at different time intervals possibly and probably twice over the period.
On the other hand LED goes on, no flickering and no light fade with an estimated life of 50000 hours versus 10000 for the fluorescent tube. There should be no more standing at the door, waiting for the lights. With LED it is instant on.
Look also at halogen spotlights - 20 x 35w halogen spots, common in a kitchen, will have an annual electricity cost of €264 while 5 W LEDs will cost €37.80 - giving better light and emitting less carbon dioxide. This is based on 7 hours over 300 days.
It makes sense.