How do I calculate the running cost of my lighting?

Taking the time to calculate the running cost of your lighting is a great way to understand your energy usage and identify any opportunities for potential savings.  This becomes especially relevant when you are looking to switch to LED technology.

The basic formula for calculating running cost is:

(Wattage ÷ 1000) × Hours Used × Electricity Cost (per kWh)

What does each part of this equation mean?:

• Wattage: The power consumption of your bulb (e.g., 10W LED)
• Hours Used: How long the light is switched on per day
• Electricity Cost: What you pay for your tariff.  This is typically measured in pence per kilowatt-hour (kWh)

To show an example - if you have a 10W LED bulb used for 5 hours a day and your electricity rate is £0.30 per kWh:

(10 ÷ 1000) × 5 × 0.30 = £0.015 per day That’s about 1.5p per day, or roughly £5.50 per year.

Below is the same equation but for a 50W halogen bulb (which would be around the same brightness):

(50 ÷ 1000) × 5 × 0.30 = £0.075 per day That’s about 7.5p per day, or over £27 per year

This above demonstrates how LEDs can reduce energy costs by up to 80–90%.

When you are calculating for multiple lights you would just need to multiply the result by the number of bulbs.  You can use a similar equation for LED strips.  You would calculate the total wattage per metre and multiply this by the length of LED strips installed.

There are a few other factors to consider when working this out:

• Usage patterns (e.g., kitchens vs hallways)
• Dimming levels (lower brightness = lower consumption)
• Smart controls or timers, which can reduce unnecessary usage

It is worth remembering that LEDs last much longer than traditional bulbs.  This means that you will need fewer replacements over time leading to additional savings.