Why Are Veins Blue?


Quick Answer

Veins are blue in color because light wavelengths are filtered differently by the skin. Blue and red light have different wavelengths, making them penetrate the skin to different degrees, which results in the blue color of the veins. Veins are the blood vessels in the circulatory system that transport oxygenated blood from the body tissues back to the heart.

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Full Answer

There are several reasons why an object is the color it appears. Two main reasons are the absorption and scattering properties of the material being distinct from those of the incoming wavelengths of the light that illuminates it. Blood looks red because of the hemoglobin inside the red blood cells. On the other hand, veins appear blue because light has to penetrate the skin to illuminate them. Red and blue are two components of light. Blue light has a shorter wavelength of 475 nm, whereas red light has a longer wavelength of 650 nm. The shorter the wavelength, the stronger the light scattered.

Plants appear green due to their cells that contain chloroplasts, which contain the pigment called chlorophyll. Deep-blue and red light are absorbed by chlorophyll, while the rest of sunlight spectrum is reflected, making the plant look green. Human eyes are sensitive to light that lies in a narrow region of the electromagnetic spectrum referred to as the “visible light.” This “visible light” is in tandem with a wavelength range of 400 to 700 nm and a color spectrum of violet through red.

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