Can a smart bulb see my other devices?
Answer first
Traffic between devices may be possible on the same local network. A guest network and client isolation limit it when the router supports those features.
Traffic between devices on the same local network may be possible. This does not mean a bulb automatically examines other devices, but the network itself may not block contact.
If a smart device has an unfixed vulnerability, a separate network limits its connections to computers and phones.
A guest network is usually the simplest way to separate devices. Check the router manual to confirm that it blocks access to the main home network.
A finer separation comes from a setting called client isolation. It stops devices seeing each other even inside the same network.