turn on/off a heat lamp, automatic.

[stonefox]

Hello

I need to turn on / off a heat lamp, depending on what the temperature is.

Is that something exists which can be purchased ready to use, or should it special is produced?

Is for use outdoors.

 

[BobK]

Yes, it exists, It is called a thermostat.

Bob

 

[Kiwi]

"Outdoors"??? Water and electricity don't work well together.

What is the application?

Type "thermostat" into ebay and you will see lots of different types. One of them may suit your application.

WARNING. Household mains electrical supply can be lethal, so don't put yourself or others at risk.
Get a qualified person to do the wiring for you.