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The smallest particle visible to the naked eye is 40 microns. To give you some perspective, a piece of hair's width can range from 40 to 120 microns.
Our eyes are sensitive to light which lies in a very small region of the electromagnetic spectrum labeled visible light. This visible light corresponds to a wavelength range of 400 - 700 nanometers (nm) and a color range of violet through red.The human eye is not capable of seeing radiation with wavelengths outside the visible spectrum.The visible colors from shortest to longest wavelength are: violet, blue, green, yellow, orange, and red. Ultraviolet radiation has a shorter wavelength than the visible violet light.he visible green light has a wavelength of about 510 nm. Grass, for example, appears green because all of the colors in the visible part of the spectrum are absorbed into the leaves of the grass except green. Green is reflected, therefore grass appears green.