What instrument is used to measure sunshine?

A solar radiometer is a device that accurately measures the sunlight's intensity, according to NASA. Simple mercury thermostats were used to measure sunlight many years ago, but these have been deemed untrustworthy.

NASA says that without sunlight, life could not exist on earth. Plants would not be able to photosynthesize and all the water on earth would be frozen solid without the energy of sunlight. A solar radiometer measures how the intensity of sunlight changes during a cloudy day or throughout the year. In the northern hemisphere, the sun becomes less intense during the winter months and is the most intense during the summer.