---
title: A Switch That Feeds Smart Bulbs Is Not a Light
description: A Home Assistant light sweep cut power to smart bulbs 75 times in 4 days, and every check said it worked. What fooled it, and how to protect your power feeds.
image: https://willcurran.com/hubfs/will-curran-brand/a-switch-that-feeds-smart-bulbs-is-not-a-light-cover-nolane.png
---

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# A Switch That Feeds Smart Bulbs Is Not a Light

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Will Curran Sep 17, 2026 · 5 min read

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[Part of: Checks that lie](https://willcurran.com/blog/series/checks-that-lie) Part 6 of 7 [Next: The Veto That Never Retries](https://willcurran.com/blog/the-veto-that-never-retries)

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![An abstract dark scene: a toggle switch linked by an orange line to three bulbs, two lit and one dark, with a timeline below marking a short gap and a long one, next to the title A switch that feeds smart bulbs is not a light.](https://willcurran.com/hs-fs/hubfs/will-curran-brand/a-switch-that-feeds-smart-bulbs-is-not-a-light-cover-nolane.png?width=1600&height=900&name=a-switch-that-feeds-smart-bulbs-is-not-a-light-cover-nolane.png)

For four days in September 2026, a room-wide "lights off" automation in my Home Assistant setup cut the power to a set of smart bulbs 75 times. Every one of those runs reported success, and every time anyone looked, the lights were on. It won for about ten seconds at a time.

The cause was one fact nobody had written down: a switch that Home Assistant listed as a light was really the power feed for the Philips Hue bulbs in that fixture.

## Two automations fighting over one fixture

Because Home Assistant saw it as a light, a sweep that turns off every light in a room turned it off too. A second automation already existed to keep that feed on. It noticed the switch was off and turned it back on. The bulbs, having lost power, rebooted and came back on by themselves.

The timings:

- **0 s:** the sweep turns the switch off. The command returns fine.
- **168 ms:** the always-on automation restores the feed.
- **9.6 s:** the bulbs finish rebooting and come back on.

Any check inside that 9.6-second window confirms the sweep worked. After it, the room is lit again. Nothing errors, and the room always ends up lit.

![Timeline chart of one run, 0 to 12 seconds. Row one: the sweep sends turn-off at 0 seconds. Row two: the feed switch is off for only 168 milliseconds before an always-on automation restores it. Row three: the bulbs are dark and rebooting until 9.6 seconds, then back on. A shaded band from 0 to 9.6 seconds: any read-back here says the sweep worked. After 9.6 seconds the room is lit again.](https://willcurran.com/hs-fs/hubfs/will-curran-brand/a-switch-that-feeds-smart-bulbs-is-not-a-light-feed-timeline.png?width=1440&height=888&name=a-switch-that-feeds-smart-bulbs-is-not-a-light-feed-timeline.png)

## "No context" does not mean a person did it

When the bulbs came back on, the Home Assistant logbook recorded a turn-on with no context. The first explanation, from the assistant I had going through the logs, was that a person was flipping the wall switch.

That was wrong. That day there were 84 turn-ons with no context, and 74 of them were my own scenes. An empty context field means Home Assistant didn't record who did it. It is missing data, not evidence that a human touched anything.

## A latched light breaks the whole room

The day before, the same reboot cycle had done quieter damage. The room's scenes had a guard: only re-apply if every light in the room is off. The rebooted bulbs were on, and they weren't lights those scenes controlled, so the guard could never pass and the scenes quietly stopped firing. The fix was to narrow the guard to the lights each scene actually owns, not to delete it.

## Where I was the bottleneck

The whole thing came apart on one line from me: that switch has to stay on, or the bulbs don't work. I had that fact the whole time. It just wasn't written anywhere a person or a tool would look.

Event production teaches this early: the crew who built the rig know things the paperwork doesn't. In a smart home, the paperwork is the device list, and it only knows what you tell it.

## What I changed

- **Excluded the feed switch** from all three automations that could reach it.
- **Labeled it where it lives.** All seven automations that touch that fixture got the same line in their description: this is the power feed, never switch it off. I wanted the warning in the automations themselves, not only in my notes.

Excluding one fixture at a time is the shortcut. The durable fix is the bulbs' power-on behavior setting: tell them to come back off, or in their last state, after power returns, so restoring the feed can't relight the room. That setting needs checking on the device itself. On another smart plug, it read back as the default after the plug had been unplugged.

## If you are about to try this

- **Find every switch that powers something smart.** Switches, relays and plugs feeding bulbs, LED strips or hubs are power feeds, whatever your system calls them.
- **Keep feeds out of light sweeps.** Better still, make them a type the sweep can't target, such as a plain switch instead of a light.
- **Label them in the system.** Put "power feed, do not switch off" in the name or description, where the next person or tool will read it.
- **Read back after things settle.** If something else can undo your change, check after its settling time, not right away.
- **Check the device, not just its state.** Is the bulb reachable? Is it drawing power? A switch reading "on" says nothing about what is downstream of it.
- **Expand groups before you trust a target list.** A light group can hide a member you meant to exclude.

## Build it yourself

What it does: stops room-wide light automations from cutting power to smart bulbs. You need Home Assistant (or any hub with room or area automations) and your list of devices. Walk the list and mark every switch, relay or plug that feeds a smart device. Exclude those from every "all lights off" action, or move them to a non-light device type. Add a plain-language note to each one. Then set the bulbs' power-on behavior so a restored feed can't turn the room back on, and re-check that setting after any power cut.

Give this to your AIHelp me audit my smart home for power feeds that my system treats as lights. I use \[Home Assistant or your hub\]. Go through my device list and flag every wall switch, relay or smart plug that powers a smart bulb, LED strip, hub or repeater, and ask me about any you can't tell. For each one, show me every automation, scene and group that could switch it off, including groups that contain it as a member. Propose an exclusion for each, or a change to a non-light device type, and write a one-line "power feed, do not switch off" description for each device and automation. Then help me set my bulbs' power-on behavior to off or last state, with a checklist to re-verify it after a power cut. When we test, read the state back only after any other automation has had time to react, and check the bulbs themselves, not only the switch. Treat logbook entries with no context as unknown, never as proof that a person did it.

If a switch in your house has been quietly fighting your automations, I would like to hear how you found it.

Filed under [Home](https://willcurran.com/blog/tag/home)

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Will Curran

I spent sixteen years building one company, and I have been in the event industry since 2007. These days I write about the technology I actually use — trucks, radios, home infrastructure, and the tools that survive past the first invoice.

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