These phrases appear to be similar, but it's important to know that "turned on" can have sexual connotations! Here are some different usages: 1.1 If someone is "turned on", it means they are very excited about something. The popular usage is to say you are "turned on" if you are sexually excited. 1.2 You can also use "turn on" literally, to start an item of technology (for example). This could be about a computer or phone. Example: Can you turn on my phone please? 2.1 You can use "switch on" to describe an action (like 1.2). Example: Switch on the computer. 2.2. "Switch on" can also be used metaphorically, to talk about your mind. If you are "switched on" you are excited/ enthusiastic about something. Or you could be very focused and know a lot of information about a topic. Example: She is switched on to learn English.

(If it is clear that you are not talking about a person, but about a piece of electrical or electronic equipment, "turn on" is perfectly normal, and doesn't carry any hidden ideas. Teenagers do not giggle if you say "turn on the lights.") In the United States, and referring to electricity, "turn on" and "switch on" are synonyms. I can't think of any difference in meaning at all. "Turn on" emphases the physical action, "switch on" emphasizes the device itself (the switch). "Switch" emphasizes the idea of something that can be completely off or completely on, but nothing in between. If we are talking about a dark room, we say that we "turn on the lights." In the special case of a computer, it is common to say "turn on the computer" or "switch on the computer," but it is also common to say "power up the computer" or "fire up the computer." Water faucets are controlled by a valve and a handle which turns. The valve is not called a "switch." You can "turn" the water on or off, but you cannot "switch" it on or off. My guess is that the usage "turn on the lights" might go all the way back to the age of gaslights, in which you turned a handle to open or close a gas valve.