There is an electrical puzzle that retired engineer Rodney Birks just can’t solve. After a lifetime spent designing instruments for cars, Birks, 72, can’t quite work out why the government and millions of households are ignoring the single, simple way we can all cut the electricity bill for lighting our homes by 90%.

It will shave nearly £2bn off the energy bills for Britain’s 25m homes. It requires just a small investment, that will be repaid within three to four months – and give you a payback lasting more than 20 years. It will stop as much as 8m tonnes of CO2 entering the atmosphere and the energy saved at peak time equates to the output of three power stations the size of Hinkley Point C.

And all you have to do is change a light bulb.

The 40 bulbs in Birks’s Swindon home have all been replaced with low-energy LEDs. He has paid as little as 92p for the bulbs – such as the candle-style one pictured below, which fits into chandeliers in his living room.

“I probably have more lights in my home than most,” he says. “LEDs used to be quite expensive but have evolved and are now cheaper than most people think. The payback time is 10 weeks if you use lights for four hours a day. Lighting was making up 18% of my electricity bill, now it’s just 1.8%.

“If you change your fridge or freezer to an A+++ appliance, you’ll probably get about an extra 20% energy efficiency. But if you change your lights, the new LEDs are 10 times more efficient that the bulbs they replace. There’s nothing like it in terms of electrical efficiency.”

Rodney Birks with the candle-style bulbs he uses in his chandelier. Photograph: Martin Godwin/The Guardian

LED bulbs are expected to last far longer than incandescent or halogen, so the savings pile up every year. Birks reckons that a typical home such as his will save £2,975 over 25 years by using them.

Many householders may have been put off by the cost. When mass-market LEDs first appeared, the price was about £9 compared with less than £1 for an incandescent. They also suffered from a perception – perhaps justified at the time – that their light was cold and icy.

Birks bought his dimmable LED candle bulbs on eBay for £6.93 for a pack of seven. When Guardian Money looked this week, there were many listed at £1 or less a bulb. Screwfix has many at £1.50 to £2, and if you are buying in bulk, there are halogen replacements for £1 each. Wilko sells classic bayonet-style lamp replacements for £2, while John Lewis charges just over £3. B&Q’s Diall LEDs – equivalent to the old 100W – were £8 when we checked in August 2018, but now sell for £6 – and you can find cheaper.

The fall in price, the improved range and, importantly, the improved lighting quality, with “warm” light options, have transformed the economics of changing over, says Birks.

His home is like millions up and down the UK – a relatively standard-size four-bedroom detached house. He says changing your lighting is ridiculously easy.

“I would like to emphasise that although I am an engineer I have not done anything difficult or technical. I want everyone to understand it is easy to do for most lights in an average home. I have just bought the bulbs and plugged them in. Anyone can do it – it is as easy as changing a light bulb!”

Households, in the long term, have no choice but to switch to LEDs. In September last year, old-style halogen bulbs were removed from sale as part of an EU-wide programme that began in 2009 with the removal of incandescent bulbs. Retailers are allowed to sell off old stock, but not buy in new ones.

What irks Birks is that while the government has funded schemes such as solar power feed-in tariffs (FITs), it is not doing enough to publicise the far greater environmental and economic savings that come from an early LED switchover.

Birks is far from anti-solar. His home is itself a beneficiary of FITs after he installed panels on his roof. “All those who signed up have got the FITs for 25 years. I’m getting £600 a year back from the government for 25 years. By my calculations, LEDs are 136 times more cost-effective,” he says.

“The government doesn’t even need to subsidise LEDs. They should be doing a major advertising campaign and telling people to switch.”

The Department for Business, Energy and Industrial Strategy says energy labels and energy efficiency standards for products such as light bulbs are helping with the transition to a low-carbon society.

“By 2020, these standards are expected to save the average dual-fuel household £100 on annual energy bills,” it adds.