This is the latest of a series of tips extracted from the forthcoming Green Business Bible e-book:

Windowless rooms (eg stores, washrooms and kitchens) are often left lit when unused - I've never worked out whether it's due to laziness or fear of the dark. This can be tackled either by providing some natural light where possible (eg by putting in some glass bricks, a skylight or a light tube), and/or installing automatic controls to switch the lights off when the room is unoccupied.