A solarimeter is a device designed to identify the radiation level of solar exposure on the Earth's surface. The primary use for the instrument is within the field of meteorological studies, specifically for identifying which weather patterns an area can expect in the near future. Solarimeters are placed atop a flat surface where they can gain exposure to the full spectrum of electromagnetic radiation coming from the Sun. As the solar radiation impacts the Earth's surface, the sensors within the device measure a full 180 degree radius around the instrument, finding the density and changes in this radiation.
Photons, the scientific designation for individual units of light, impact the device. A solarimeter uses either a chemical-based system or physical instruments to determine these photon levels. Within the spectrum of light, ultraviolet light as well as the visible wavelengths can be identified by the device, causing reactions to the chemicals or instruments.
A chemical solarimeter device utilizes a solution made from different chemicals: malachite green leucocyanide, monochloroacetic acid, or potassium ferrioxalate. Radiation is measured from the absorbed light in a process known as quantum yield identification. In this way, a solarimeter is able to determine the total level of electromagnetic radiation, from the light spectrum to the heat impacting the Earth's surface.
On the other hand, some solarimeters use physical instruments to identify the radiation. These include bolometers, photodiodes and thermopiles. Bolometers are the most basic, using a piece of metal hooked to a heat sink which allows changes in temperature to be identified. Photodiodes are more modern designs, utilizing the concept of solar power to transfer light energy to an electrical current, measuring the level of radiation. Likewise, thermopiles are capable of converting heat into electrical current, which also finds the radiation level.
Solarimeters rely heavily on the actual position of the Sun in order to get the best possible read. When the solar radiation is coming from its zenith, directly above the device, the readings are completely accurate and readily identifiable. However, between the angles of 0.5 and 60 degrees, a proportional determination must be made. Unfortunately, if the Sun is positioned at 90 degrees or greater, no reading can be measured.
One major visual component of a solarimeter is a small glass dome placed atop the device. This allows proper readings to occur within the range of 300 and 2,800 nanometers, considered to be the ideal parameters to make a measurement. In addition, this glass dome supplies a simple protection shield from other phenomena such as rain or snow.