Solar Radiation: UV, Visible & Infrared Spectrums - Essay Sample

Introduction

Solar radiation refers to the radiant electromagnetic energy emitted by the sun. that energy is responsible for all the light and heat for earth inhabitants especially the crops for photosynthesis. According to Perez et al. (2012), solar radiation or electromagnetic energy is emitted as a group of three layers that comprise of the ultraviolet spectrum (UV), the visible spectrum, and the the infrared spectrum. However, the total energy emitted by the sun reaches the earth's surface in different proportions. 49.4% of the total radiation comprises of infrared radiation, 42.4% of visible light, while the remaining 8% comprises of ultraviolet radiation.

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Over time scientists have proven that several factors determine the intensity and amount of solar radiation in certain locations. Such factors include latitudes, time of the day, altitude (height above sea level), amount of cloud cover, and season. Apart from these factors, it is important to note that not all of the radiation produced by the sun hits the earth as most of it is taken up by the atmosphere (Wong & Chow, 2001).

Measurement of Solar Radiation

Solar radiation is measured in frequency or wavelengths. Light travels in form of waves and wavelength refers to the distance between peak and is expressed as nanometers (nm). On the other hand, frequency refers to the number of wavelength cycles formed in one second. Light bands with short wavelengths have high frequencies while light bands with long wavelengths have low frequencies (Gueymard, 2004). The energy carried by a wavelength is directly proportional to the size of the wavelength (Gueymard, 2004). That means that short wavelengths have higher energy than long wavelengths. This fact explains why ultraviolet radiation has more energy than infrared radiation. Due to their higher energy, short wavelengths cause more damage than long wavelengths. That is noted in ultraviolet radiation which causes damage to DNA and other vital cellular structures.

Ultraviolet Radiation

Ultraviolet radiation is categorized into three groups as shown in the figure below.

The three bands of wavelengths have the ability to directly affect the DNA of living organisms especially in aquatics as well as produce photo-chemicals (Iqbal, 2012). UV-C band comprises of wavelengths between the range of 100nm and 280nm. The radiation produced by this band comprises of only 0.5% of the total solar radiation but has the potential to cause the most damage to living organisms. Fortunately, majority of this band of short wavelength is taken up (absorbed) by the stratospheric gases in the ozone layer hence only a small proportion is noted in the earth (Iqbal, 2012). On the other hand, UV-C is popularly understood as a high energetic photo-activating type of radiation and only a small proportion of it is taken up by the stratosphere. It is feared for its ability to cause skin cancer in humans and impede the process of photosynthesis in plants. The depth at which this band penetrates the water is influenced by the turbidity. Lastly, UV-A has the least energy since it has the longest wavelengths of range 320nm to 400nm (Iqbal, 2012). This band is not taken up by the ozone layer but is blocked from reaching the earth's surface by cloud cover. Due to it's ability to induce fluorescence in some materials, it also known as blacklight. It causes sunburns in humans and affects photosynthesis in plants by about 70% by impeding flow of electrons.

Infrared

Infrared radiation is perceived as being on the contrary position of the electromagnetic from the ultraviolet light. According to Muneer (2007), infrared radiation has wavelengths of about 700nm and is responsible for almost half of the total solar energy. One of the key features of infrared radiation is that it is easily absorbed by water and carbon dioxide then converted to heat energy. The long wavelengths excite atoms in the compounds that absorb them and resultantly warms the earth's surface. Due to the long wavelengths, they are reflected more than ultraviolet and visible light. The higher reflection enables infrared light to carry heat between water, earth's surface, and air (Muneer, 2007). However, the long wavelengths reduces the ability of infrared to penetrate water hence about 90% of it is absorbed within the first 100cm after entering water surface

Importance and Potential Effects of Solar Radiation

Solar radiation supplies light, heat, and energy required by all living organisms. In the absence of solar radiation, scientists estimate that the earth's surface would be colder by about 32Oc. Importantly, solar radiation provides light which predators depend on for hunting. Human beings also depend on the visible spectrum (light) to carry out their activities. Further, solar radiation is vital for the light utilized by crops for the process of photosynthesis. The different light wavelengths are absorbed by different plants that utilize different light wavelengths for the process of photosynthesis (Iqbal, 2012)

The level of solar radiation at any time is dependent on the day time and the angle of the sun from the earth. The bigger the angle, the more the sunlight is absorbed by the ozone layer. Also, cloud cover and air pollution affect the radiation levels. Increase in radiation levels increases ultraviolet light which increases the risk of permanent damage to DNA, overheating, and damage of photosynthetic structures. In addition, increase in solar radiation increases water temperature hence less dissolved oxygen available for aquatic animals. On the other hand, decrease in solar radiation causes phytoplanktons to consume oxygen instead of producing it (Muneer, 2007).

Conclusion

In conclusion, the discussion surrounding solar radiation is vital now than ever especially with the likelihood of global warming seeming a reality than ever. Even though the science world is yet to come to a consensus on the true risk of climate change, it is vital that the typical solar radiation levels remain in status quo. Therefore, air pollution should be maintained at minimal levels.

References

Gueymard, C. A. (2004). The sun's total and spectral irradiance for solar energy applications and solar radiation models. Solar energy, 76(4), 423-453.

Iqbal, M. (2012). An introduction to solar radiation. Elsevier.

Muneer, T. (2007). Solar radiation and daylight models. Routledge.

Perez, R., Kivalov, S., Schlemmer, J., Hemker Jr, K., Renne, D., & Hoff, T. E. (2010). Validation of short and medium term operational solar radiation forecasts in the US. Solar Energy, 84(12), 2161-2172.

Wong, L. T., & Chow, W. K. (2001). Solar radiation model. Applied Energy, 69(3), 191-224.