When the clocks go back each October, we gain an hour of sleep and lose an hour of evening daylight. The practice of moving the clocks forward in spring was introduced partly to save energy, by making better use of daylight at the end of the day so there would be less need for artificial lighting.

But the lights in our homes have changed dramatically since the UK first adopted summer time in 1916 – and the change over the past decade or so has been especially rapid. A modern LED bulb can produce as much light as an old-fashioned 100-watt bulb while using a fraction of the electricity. This raises a question: in an age of energy-efficient lighting, does changing the clocks still save us much energy?

The UK introduced the clock change in 1916, during the first world war, to conserve fuel and enhance productivity. Moving the clock one hour forward would delay sunset relative to the time, and hence should save energy by reducing the need for lights after dark.

After a few tweaks in the 1960s and 70s, the current scheme has been in place since 1980, with clocks going forward on the last Sunday in March and reverting to Greenwich Mean Time on the last Sunday in October. Since the mid-1990s, these dates have been harmonised across the EU to reduce any disruption in travel and business.

But whether the clock change delivers the energy savings originally intended remains uncertain. A 2026 House of Commons Library report found that the effects of clock changes on energy demand are inconclusive. The potential savings from reduced lighting use can be offset by changes in heating and cooling demand.

Modern lights use a lot less electricity

Incandescent bulbs, which produce light by passing an electric current through a tungsten filament, are highly inefficient. Most of their energy goes into generating heat – of the electricity they consume, just 5% to 10% or so is turned into light. These bulbs were phased out of the UK market between 2009 and 2012, followed by most halogen bulbs (a similar technology) in 2021.

Those bulbs were replaced by light-emitting diodes, or LEDs, now the most efficient light bulbs in widespread use. An LED bulb producing the same amount of light as a 100-watt incandescent bulb (about 1,520 lumens) would use just 13.5 watts – an electricity saving of around 86%. Almost every light you see today is based on LED technology.

This means that producing a given amount of artificial light now requires much less electricity than it did when daylight saving time was introduced. But that doesn’t, by itself, tell us how much energy changing the clocks saves today.

Lighting has historically been only a small percentage of household energy consumption. Today, it accounts for about 4% of household electricity consumption in the UK, or about 1% of overall household energy use (which includes gas for heating), according to government estimates for 2025. However, overall household energy consumption has in general declined since the 2000s, mainly due to the adoption of other energy-efficient measures.

More efficient lighting can also change how people use it. Lower running costs may encourage people to use more lights, especially for decoration, or to leave them on for longer – economists call this a rebound effect.

That’s why we can’t only look at how efficient light bulbs have become. We have to consider how much electricity the clock change saves across the energy system as a whole.

Only modest energy savings – at best

Modern life is significantly different from when the clock change was introduced in 1916. We have renewable energy, electric cars, and homes and offices packed with electronic and computer equipment.

A study from 2018 that combined 162 estimates from 44 studies found average energy savings of about 0.34% during daylight saving time. A further study from 2025 suggests that the original justification for daylight saving time as an energy-saving measure is increasingly uncertain. Broadly, research suggests reductions in lighting demand are most likely to be balanced by increased heating and cooling demand. Any energy savings are likely to be relatively small and depend on factors beyond lighting efficiency.

The European Parliament voted in 2019 to abolish the twice-yearly clock change, although implementation has stalled because EU countries have not agreed whether to keep permanent summer or winter time.

The move from incandescent bulbs to LEDs has hugely reduced the electricity needed for lighting, weakening one of the original reasons for changing the clocks. But the available research does not offer a simple calculation of how much energy the UK or similar countries would save or use if the system was abandoned.

The original rationale was straightforward: shift daylight into the evening hours and reduce the need for electrical lights. Today, much more efficient bulbs mean that the potential savings from clock changes are smaller than they once were. Whether that makes daylight saving unnecessary depends on the wider effects of changing our clocks – and the evidence on those effects remains inconclusive.