Smart lighting is bulbs, lamps and light strips that join the home network, so that the owner can switch them on and off, dim them, change their colour or put them on a schedule, from a phone app or by voice. Each smart bulb contains LED lights, a small chip that controls them, and a radio.
There are two common designs. In the first, each bulb has a Wi-Fi radio and joins the home Wi-Fi directly, like a phone. This is simple, and needs nothing extra. But dozens of Wi-Fi bulbs crowd the home router. In the second design, the bulbs use a low-power radio such as Zigbee, Thread or Bluetooth, through an IoT wireless chip. A small box called a hub, or bridge, is plugged into the router. The bulbs send and receive messages through the hub. They also pass messages on for each other, so that a bulb far from the hub can still be reached. This is a mesh network.
How does a bulb dim or change colour? The chip in the bulb switches the LEDs on and off hundreds of times a second. The longer each "on" moment lasts, the brighter the light looks. A colour bulb has red, green, blue and white LEDs, and mixes them at different strengths to make any colour.
Consider a family in Dehradun before Diwali. They put colour light strips along the balcony and change two living-room bulbs to smart bulbs. In the app, they set a schedule: at 6 p.m. every evening, all the lights turn on in warm gold, and at 11 p.m. they turn off. On Diwali night, a family member says to the smart speaker, "Make the balcony lights red and green." The voice assistant turns the words into a command and sends it to the lighting maker's cloud. The cloud passes it to the hub, and the hub tells the strips to change colour. The family can also change the lights while they are away from home, because the phone app reaches the hub through the cloud, as described in IoT architecture.
Why do people buy smart bulbs? For convenience, for mood and festival lighting, and to save electricity. LEDs use much less power than old bulbs, and schedules turn lights off when no one needs them. Some people also use schedules while they travel, so that the house does not look empty.
Bulbs from different brands used to need different apps. The Matter standard, one of the shared connectivity standards, aims to let one app run bulbs from any maker.
The same technology lights offices too. There, the lights are usually part of a building system, or are run from a room control panel in a meeting room, together with the room's screen and sound.