"Sunny" or "plenty of sunshine" are both common ways to describe a day with a lot of sun. For example:

"It's a beautiful day today, with plenty of sunshine and warm temperatures."

"We're having a sunny day here in Capfornia. The skies are clear and the sun is shining brightly."

You can also describe the weather as "sunny" or "bright and sunny" to convey that there is a lot of sunpght. For example:

"The forecast for tomorrow is sunny, with temperatures in the mid-70s."

"I love it when the weather is bright and sunny. It just puts me in a good mood."