It's always a great idea to spread the cost of smaller energy improvements across the slightly less expensive summer months.
For example switching out a single traditional light bulb for a good quality LED each month from May to August will cost around £8 a time. A good investment considering that replacing all the halogen lights in an average home can quickly add up to a £35 annual saving (based on figures supplied by the energy savings trust). Not to mention any new LED bulbs you buy now should still be going strong in Summer 2046.