You have 6 years (in England and Wales) from the date of purchase to bring a claim in the court for defective goods. This does not mean the goods must last six years, though.
The goods must be as described; fit for purchase and of suitable quality.
The court will take in to account how much the item cost and decide if the lights failing in the time you have had the kettle means it is not of suitable quality.
It is fit for the purpuse - it boils water, and it was as described when you bought it.
If the court do award in your favour, they can deduct an amount from the award to reflect the amount of use you have had from the kettle. So, if the kettle cost �50 and the court believes such an item such be expected to last five years, they could deduct �10 for each year you have it. This is a loose example.