Suppose I want to control my room lights over WiFi using mobile phone. But I also want to control them by using the switches in my room to which they are connected. Is it possible to implement them both? I watched and read a couple of tutorials on Home Automation over WiFi but they only focused on controlling the home appliances remotely.
If the appliance itself is switched, this will not be possible.
If it is a remote operated switch (generic mains switch), you can try to wire it like a cross circuit, with your remote control switch and the mechanical wall mounted switch each controlling one wire ('to' and 'from', naively speaking). Note that some appliances do not fully shut down if just the non-phase wire is disconnected. You may experience flickering.
There are a couple of popular options for 'smart lighting':
Smart bulbs, like the Philips Hue, where the electronics are embedded in the bulb itself. Smart bulbs often have various features like multiple colours, built-in dimming (even without the wall switch necessarily being a dimmer).
Smart switches, where the switch itself contains the electronics, and you just use a regular light bulb. You don't tend to get the bells and whistles like colour changing, because the switch only knows 'on' or 'off' (or in some cases, dimming too).
There's some discussion about the benefits of each at Is it better to control smart lights or smart light switches/fixtures?
If you wanted to have a functional switch, you'll need a smart switch rather than a bulb. As hardillb points out, when a smart bulb is switched off, its circuitry receives no power and it just doesn't function. Your switch either has to handle the 'smart' aspect, or have some way of communicating it to the bulb without actually turning the bulb off. The Lutron Caseta is an example of the former, and the Hue dimmer switch is an example of the latter.
Each option has tradeoffs which you should take into account; using the Hue dimmer locks you in to Hue bulbs, but installation is simpler. Using a full 'smart switch' requires modification of your house's wiring, which may or may not be suitable depending on your circumstances and skill.
Most Smart lighting systems require that there is power to the bulb at all time. This means that if you turn off the wall switch then they will no longer work.
Companies like Philips with their Hue and Ikea with their Tradfi products have produced light switch like control devices which can be stuck to the wall next to the existing switches (not totally replacing them as you should still be able to turn the sockets off to change the bulbs). These devices allow you to interact with the lights in the "traditional" way while still allowing full control.
They also normally allow you to add additional wall switches without having to run cables since they are battery powered.
I believe the Ilumi light bulb gets as close to this as you can get. It uses bluetooth instead of wifi, but the principle is mostly the same. Basically, the situation is the following:
If the light switch is turned on, you can control the lights over bluetooth. If the light switch is turned off, the light (and the whole system) is off no matter what.
You can use the light switch to turn the light on or off
- if the light is on, turning the switch off turns the light off
- if the switch is on but the light is off, turning the switch off then on again, turns the light on
- if the switch is off, turning the switch on turns on the light
In order to achieve this, they have the following properties:
- You can set a default color and intensity in the app, which is what the bulb will go to at "startup"
- This information is stored in the memory that is in the bulb itself
- The bulb was built to survive cutting the power
With these things in mind, it probably makes a lot of sense that the bulbs use mesh networking instead of a hub.
I wouldn't exactly recommend getting these bulbs. That's mostly due to the behavior of the company, though. The mesh networking also isn't always the best, but it has definitely gotten better throughout their updates. However, I do still think that being able to use your normal light switch is the killer feature that all competitors seem to be missing.