Lightbulbs connected to a hue bridge are repeaters–but only for other devices attached to the same bridge. They essentially form their own mini network. So they won’t help with nearby sensors.
Zwave lightbulbs like those from Linear and aeotec typically are repeaters – – but only for Z wave. These can actually be very useful in some specific use cases like getting zwave signal down basement stairs or across a garage.
zigbee bulbs connected directly to the ST hub
Zigbee lightbulbs like hue or Osram if connected directly to the SmartThings hub without using a bridge shift from the ZLL profile to the ZHA profile and then do typically act as repeaters for other ZHA devices. We have a number of members doing just that. However, many members also report that the zigbee bulbs are unreliable repeaters. Sometimes they clearly repeat for other ZHA devices, and other times they don’t. It may be a timing issue. It certainly very frustrating because the bulbs will show on a zigbee map as a repeater.
SmartThings engineering has investigated and determined that some of these brands, including the Osram, have a limited buffer size which can get flooded, causing messages that were due to be repeated to be lost. This probably explains the intermittent nature of the problem.
Note: OSRAM LIGHTIFY bulbs have a known firmware issue that can occasionally cause them to fail as ZigBee repeaters. This can potentially cause other ZigBee devices to fail to update and/or respond.
(However, if Hue bulbs are connected without using the bridge they cannot be individually reset without using a separate device like the Lutron connectable bulb remote. You also need a different device Handler than the official one (which assumes the bulbs are connected to the bridge). For these reasons, SmartThings support recommends using hue bulbs only with a Hue bridge. But some members do connect them directly.)
Because GE Link lights have a known firmware issue that can cause some of them to drop off the network every few weeks, they are generally not recommended as repeaters for other devices.
A few Zigbee brands have not implemented the full protocol for bulbs, and may not act as repeaters.
So the short answer for zigbee light bulbs is that having one directly connected to the hub may help strengthen the ZHA mesh but you should not use it as the only ZHA repeater in that zone as it may miss messages from other device classes from time to time.
For board discussion of some of the inconsistency issues with bulbs connected directly to the hub, see the following thread:
WiFi bulbs do not act as repeaters.
Bulbs that use their own protocol like TCP may repeat for each other, but will not repeat for anything else connected to SmartThings.
So many lightbulbs do act as repeaters, and sometimes they are the most practical choice particularly in rooms that have a lot of potential signal blockers like cars in a garage because the bulb is typically placed much higher in the room than a pocket socket or even a light switch, and consequently offers additional lines of sight. But they introduce additional issues and there’s also the question of whether they are really going to be left on power all the time. So I usually bring them up if the particular use case under discussion seems like it would benefit from them, and otherwise not.
After you add any new device to your network, including a bulb intended to act as a repeater, you need to update the address tables or other devices will not use it.
For more information about repeaters in general, see:
As long as a bulb is drawing power, even if it looks like it is off, it will still be able to act as a repeater. Smart bulbs are not intended to be used with switches that cut the power completely – – this can shorten the bulb life considerably.
selecting switches to use with smart bulbs
For discussion of the best switches to use with smart bulbs, see the following: