A smart bulb never truly switches off. Even when the light is out, it keeps listening on your Wi-Fi, Bluetooth or Zigbee network so it can react the moment you tap the app or ask a voice assistant. That waiting state, known as standby, draws a trickle of power around the clock, every day of the year. So the fair question is whether a smart bulb actually saves you money, or whether the quiet draw while it sits idle simply cancels out the benefit.

Even switched off, a smart bulb keeps drawing power to stay connected

Retained EU ecodesign rules, still in force in Great Britain, cap the networked standby power of a connected light source at 0.5 watts, listed as Pnet in the annex, and that figure has to appear on the box. It is a legal ceiling, not a suggestion.

The better brands sit well below it. Philips quotes around 0.10 W for its Hue A60 E27 (1,100 lumens, 8.1 W when lit); Ikea about 0.2 W for its KAJPLATS E27 (7.8 W when lit). Between the most efficient bulb and the legal ceiling the idle draw varies fivefold, so in practice a single smart bulb sips somewhere between 0.1 and 0.5 W while it waits.

The line to check on the box before you buy

The rules require that standby figure to be printed on the packaging, in watts to two decimal places. It is not hidden away: you just have to look for it among the technical specifications.

  1. Look for the "standby power" or "networked standby" line on the product sheet, given in watts to two decimals.
  2. Compare the number, not the brand name: the gap between 0.10 W and 0.50 W is paid every night, for years.
  3. Favour models under 0.2 W if you plan to fill the house with connected bulbs.

Good to know: the gap between 0.10 W and 0.50 W looks trivial on paper, but multiplied across ten bulbs and years of round-the-clock running it becomes a fixed line on your bill.

What that standby costs over a year

At 0.5 W left connected all year a bulb draws about 4.4 kWh; at 0.2 W, a little under 1.8 kWh. On the current price cap unit rate of about 26.11p per kWh, a single bulb on standby costs between 23p and £1.14 a year. Trivial, as long as it is only one bulb.

Yearly cost of standby alone, by number of connected bulbs (full year, 26.11p/kWh)
Connected bulbs At 0.2 W each At 0.5 W each
1 bulb £0.46 £1.14
5 bulbs £2.29 £5.72
10 bulbs £4.58 £11.44
20 bulbs £9.15 £22.88

Want the figure for your own home? Enter how many bulbs you keep connected, their quoted standby power and your unit rate:

Work out your yearly standby cost

Estimated cost

£/year

≈ kWh a year, on standby alone

Selectra

Anyone trying to work out how to save electricity at home tends to overlook exactly this kind of small, constant draw.

The paradox: it can cost more off than on

The sums flip for bulbs you barely use. An 8 W bulb switched on for one hour a day burns about 2.9 kWh over a year; leave that same bulb on 0.5 W standby for the other 23 hours and it quietly gets through more than 4 kWh while off. Put plainly, the bulb can cost more doing nothing than doing its job.

Fill a house with them and the total climbs fast: ten smart bulbs kept online all year draw, on standby alone, from about £4.60 to roughly £11.40. That is money you pay whatever you do, even on days you never switch a single light on.

Against a plain LED, the gain is in the control, not the efficiency

One thing needs saying clearly: when it is lit, a connected LED uses the same power as an ordinary LED of the same brightness, around 8 to 9 W for 800 lumens. It does not light your room any more efficiently. Any saving comes only from how you use it.

  • Switching off a forgotten light from your phone claws back the best part of 60p a year on a single 8 W bulb left on an hour too long each evening.
  • Scheduling when lights come on and go off trims real hours; cutting four bulbs half an hour earlier saves a little over a pound a year.
  • Dimming down to half brightness for a few hours a day shaves a few more pounds off the total.
  • Do not expect the technology itself to cut your bill: lit, a smart bulb draws like any other LED.
  • Do not scatter smart bulbs where they earn little: there, standby wipes out any saving.

The honest verdict: you buy a smart bulb for the convenience, not to shrink your electricity bill. Swapping halogens for LEDs across ten fittings saves the best part of £100 a year, far more than any amount of automation.

The switch trap, and depending on the app

If you want to kill standby altogether you can cut the power at the wall switch, but then the bulb goes dumb: no app, no voice, no schedules. Many homes end up leaving the switch permanently on and quietly abandoning the smart features they paid for.

The middle path is a smart switch or an in-wall module: you keep physical control and concentrate one standby draw per fitting instead of one per bulb. Watch the cloud dependency too, because if the service shuts down the smart features vanish, whereas bulbs on a local protocol (Zigbee, the Matter standard) run through a hub in your home and tend to last longer. It is also worth seeing where a smart bulb sits next to everything else that runs quietly at home, which our guide to energy-saving lightbulbs sets out.

  • The bottom line
  • Read the standby figure on the box and pick a model under 0.2 W.
  • Keep genuinely smart bulbs to the rooms that need them.
  • Use a smart switch so you do not lose control when you cut the power.
  • Buy a smart bulb for the convenience and the tailored light, not for the bill.