The visible light spectrum ranges from 700 to 400 nanometers, with infrared at the lower end and ultraviolet at the higher end. Each color represents a different wavelength, with white light being a combination of all. Reflection of certain wavelengths creates colors, while black is the absence of visible light. Infrared and ultraviolet light can’t be seen by humans, but false-color images can help understand them. Ultraviolet light can be harmful or beneficial, used to treat seasonal affective disorder and promote plant growth.
The visible light spectrum is a range of light visible to the human eye and is responsible for the colors we see. The spectrum consists of light waves ranging from about 700 nanometers to 400 nanometers. Outside of this visible light spectrum, at the lower end of the frequencies, is infrared light. At the higher end, invisible light is known as ultraviolet.
In the visible light spectrum itself, each color seen by the human eye represents a slightly different wavelength of light, and the principal divisions of those wavelengths can be seen as a rainbow. In physics, a wavelength is defined as the distance from one point along the wave to the next similar point, usually measured between crests or troughs. A wavelength at the lower end will be a shade of red. In the center, the wavelengths will be represented as green or blue, and at the upper end as a shade of purple.
White light is obtained when all wavelengths of the visible spectrum are combined together. It is the most common form of visible light. Black, of course, is the absence of visible light. White light can be split and separated into various wavelengths, or light can be absorbed and reflected only at certain wavelengths.
The reflection of certain wavelengths across the visible spectrum is the most common way to see colors. For example, if a person is looking at a book with a red cover, they are actually seeing a reflection of red light waves being beamed at them. The other wavelengths of the visible spectrum are absorbed in the book cover. Only red, which is a lower frequency wavelength, is returned to the viewer. If the cover of the book were black, it would mean that no waves on the visible spectrum are reflected.
While there are things like infrared detectors and ultraviolet light that reveal images that people can see, these don’t truly allow humans to see beyond the visible spectrum. Rather, these instruments simply provide an equivalent of the visible spectrum, using false-color images. This helps people understand that there are other wavelengths of light in the universe that can’t be seen, and it can also help explain things like weather patterns and astronomical observations. Such techniques are also used in forensic science to reveal organic material that otherwise could not be seen.
While some forms of light fall within the visible spectrum, that doesn’t mean they don’t impact living organisms. For example, ultraviolet light is often responsible for sunburn and skin damage, but it can also be beneficial. Ultraviolet light is often used to treat seasonal affective disorder in humans and is used in plant nurseries to promote greenery growth.
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