Words To Know

• Radiometer - an instrument used to measure the amount of electromagnetic radiation (for more, check out the lesson on electromagnetism).
• Solar Irradiance - is the total power per unit area produced by the sun in the form of electromagnetic radiation.
• Watt - a derived unit of power (J/s; joule per second) that is used to express the rate of energy transfer with respect to time.
• Joule - a unit of work or energy, the work to produce power.
• Zenith - refers to an imaginary point directly “above” a particular location.
• Erythema - superficial reddening of the skin, usually in patches, as a result of injury or irritation causing dilatation of the blood capillaries.