> With kids, it has turned out to be an energy saver.

I wonder, though. Most folks now have LED bulbs, so being diligent about turning off lights isn't as much of a savings as when I grew up and everything was incandescent. Also, if you train kids that the lights go on and off on their own, are they more likely to just never turn anything off?

My teenage kids have friends over frequently, and while my kids have been reasonably well-trained to shut things off, close doors after they go through, etc., their friends are generally pretty bad stewards of my electricity. (And it's not malice; they just don't think about it.)

I like the idea of automating efficiency into the system, but there's always a human element. And that seems to require repetition.

> I wonder, though. Most folks now have LED bulbs, so being diligent about turning off lights isn't as much of a savings as when I grew up and everything was incandescent.

It's very convenient to have the light come on automatically in stairwells and lavatories. But you are right about it taking much longer to pay back. My calculation is that compared to having the LED bulb on continuously it pays back in about two years.

I have several infra red motion detector bulbs in stair wells and in the pantry as well as 'radar' bulbs in several other places (these detect movement by the disturbance in a low level high frequency radio signal).

> (these detect movement by the disturbance in a low level high frequency radio signal).

I'd never heard of this before. One of my former managers is really into Home Assistant and has done a lot with his setup, but I think all of his motion detection was IR. How's your 'radar' setup? Do you get a lot of false positives/negatives? How's the distance on its detection?

He's talking about the motion detector things that are a drop in replacement for switches. You see them often in rooms in commercial buildings.

Something like this https://i.ebayimg.com/images/g/nvAAAOSwEK5fmkrH/s-l1600.jpg

> He's talking about the motion detector things that are a drop in replacement for switches.

No I'm not, but those work too.

This is what I bought: https://www.ebay.com/itm/153285261299

It is described as a radar sensor because it uses a high frequency oscillator and monitors the change in the signal due to things moving in the electromagnetic field. Imagine the effect of waving your hand near the aerial of a radio receiver when the signal is weak.

>It's very convenient to have the light come on automatically in stairwells and lavatories.

Until you're drunk AF and trying to take a piss (or whatever it is you're doing) at 1am and then the "smart" light blinds you.

Here's my solution: https://www.ebay.com/itm/265164805260

A 4 watt LED lightbulb left on constantly for a year would consume 52 kWh of energy, costing ~£7.50 at UK prices, releasing ~9.5 kg of CO2, the equivalent of driving 23.5 miles in the average US passenger vehicle.

There are good reasons for turning off lights in the house (getting a good night's sleep is one!) but saving energy is no longer one of them.

There are a lot of light bulbs, though. The LED switch has had meaningful impact on US residential energy usage [0]. IEA reports 38B in LED sales in 2015-2020 [1]. Averaging $10 (high) per bulb, that's 3.8 billion bulbs (including non-residential).

Leaving a light on doesn't matter much. Leaving billions on can clearly have an impact.

[0]: https://archive.is/RldJl

[1]: https://www.iea.org/reports/lighting

The billions of bulbs have the same proportional impact on the national energy budget as the few in your home have on yours, that is practically nothing.

See David MacKay's Sustainable Energy Without The Hot Air, chapter 19. https://www.withouthotair.com/c19/page_114.shtml