There are two main types of energy efficient light bulbs available in the UK. Compact Fluorescent Lamps (CFLs) and Light Emitting Diodes (LEDs). Both CFLs and LEDs are a cost-effective option for most general lighting requirements. Replacing a halogen light bulb with an LED of the same brightness will save you up to £2 per year.
LEDs are available to fit most fittings and are particularly good for replacing spotlights and dimmable lights, they are more efficient than CFLs and will save you more money in the long term. By replacing all bulbs in your home with LED alternatives, you could save about £40 a year on your electricity bills (Energy Saving Trust).’ (https://energysavingtrust.org.uk/advice/lighting/).
When considering how bright you need the light to be, you should look for the amount of lumens and not watts as lumens measure the total amount of light emitted by the bulb while watts measure the amount of power consumed by the bulb. It is possible to check how bright (lumens) any given bulb’s wattage is by consulting charts. Here is one that can be used to do that.