Correct although you could also say "you brighten my day". As others have said, "You made my day" although that is usually used when someone has done something that specifically made you happy (even if what they did was arrive). You can also say "You are a ray of sunshine" which works even in a dismal place since they don't always get sunshine and it is a particularly special and welcome thing! If someone is the only thing you look forward in a place that is unhappy or dreary, you can say they are "a breath of fresh air"--which means that having them there is a wonderful and positive change from what (or who) you were dealing with. Sometimes if someone new comes to a situation and you like how they think because they think or behave differently from what you are used to, you would say they are a "breath of fresh air".

You can also say "you made my day". Avoid using "sunshine" for a person in the UK. It's a little disrespectful and is usually used ironically.

Yes, it’s ok. If you’re referring to something specific that they did to make you happy you can say “you’ve made my day”. You can also call them ‘sunshine’ as a pet name.