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What is a Solarimeter?

By Jason C. Chavis
Updated: May 23, 2024

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.

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Discussion Comments
By miriam98 — On Oct 17, 2011

@allenJo - I’ll stay out of this debate for awhile. I’ll just note that I think the ability to measure solar radiation is extremely useful for determining other things that are clearly related to the sun, like solar flares.

I’ve heard we’ve had some powerful solar flares, which are giant explosions in the sun, and that these in and of themselves could have some disastrous consequences for the inhabitants of planet Earth.

I’ve read that solar flares could mess up our GPS communications or affect our electrical grid or things like that. I believe that the solarimeter could function like a fire alarm which would allow us to know that such an event was taking place, and allow utilities to put emergency actions in place.

By allenJo — On Oct 16, 2011

@NathanG - Since you said that you’re not a scientist I’ll give you the benefit of the doubt about the sincerity of your convictions.

However, the majority of scientists believe that the warming phenomenon is man-made. I am sure that they all know what a solarimeter is and that they have taken solar radiation measurements into account in their calculations.

From what I’ve read, however, the sun’s radiation exposure has not always correlated with the solar temperature. So I don’t think that you can make a firm argument that the sun alone is the cause.

By NathanG — On Oct 15, 2011

I think that a solarimeter is a very useful device in the ongoing global warming debate. One of the ideas advanced by the contrarian scientists (those that say global warming is not man-made) is that global warming is accounted for by the sun, and nothing more.

These scientists point to solar activity in the sun, either cooling trends or warming trends, which seem to coincide with similar cooling and warming trends in the Earth.

While I am not a scientist, to me it would make sense, since the sun is after all the primary source of warming on the Earth. Solar radiation measurements taken by a solarimeter would be the most useful tool in that sense, not just readings of how much carbon dioxide is in the atmosphere.

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