The electromagnetic radiation and its spectrum

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Light is only our conception or interpretation of the energy potential of electromagnetic radiation.

Ted Orland’s Compendium of Photographic Truth, „a collection of moral principles, axioms, and tenets every photographer should face„, says: „Distant objects cannot be photographed with short exposure times – light travels only a good 300 km in 1/1,000 of a second.“ Crazy, right? However, there is a kernel of truth in this statement, as light carries the optical information of our surroundings. Without light stimuli, visual perception and photography would not exist. So we have compelling reasons to examine this essential component of all visual processes more closely. If we do this, we first have to take note of the fact that there is no such thing as an independently tangible substance as implied by the term light. What we traditionally call light is only the section of the electromagnetic radiation surrounding us for which we have developed a certain sensitivity due to our physiology. The totality of this radiation we call the electromagnetic spectrum, and we subdivide it as follows:

Gamma radiation ( 1 femtometer - 1 picometer, 10-15 - 10 -12 m).
X-ray radiation (1 Ǻngström - 1 nanometer, 10-11 - 10-9 m)
Ultraviolet radiation (< 1 micrometer, 10-8 - 10-7 m)

Visible light (380 nanometers - 780 nanometers)

Infrared radiation (> 1 micrometer, 10-6 - 10-5 m)
Terahertz radiation (< 1 millimeter, 10-4 m)
Microwaves (1 millimeter - 1 centimeter, 10-3 - 10-1 m)
Radio and television radiation (< 10 meters - < 10 kilometers, 100 - 104 m)
High, medium and low frequency alternating currents (> 10 kilometers, 105 - 107 m)

In view of this wide bandwidth, the sensitivity of our visual perception apparatus appears rather low. The range of 380 nm (0.00000038 meter wavelength) to 780 nm (0.00000078 meter wavelength) lies between ultraviolet radiation on the short side and infrared radiation on the long side, making up less than 1% of the total spectrum. The discipline of optics is that branch of science that explores the part of electromagnetic radiation that is visible to us.

Why are we sensitive to this narrow part of the spectrum? Well, radiation in the wavelength range below 380 nm (ultraviolet) is so energetic that it quickly destroys the photopigments in our eyes and, within a slightly longer period of time, clouds the lens of the eye yellow. Some species of birds and insects have developed a sensitivity to UV light but die before it can do measurable damage. Larger mammals, like us, have a longer life span and therefore must adapt their visual systems to these damaging influences. On the other side of the spectrum, wavelengths above 780 nm are primarily thermal radiation (infrared) and this gives little information about the nature of objects. On infrared film, a face looks like a hot iron skeleton, and therefore there is little to learn about the world under daylight based on the long-wavelength radiation. Therefore, our vision primarily concentrates on the middle region, which interacts with matter most strongly and differently, providing us with the most information about the world.

Wavelength: The distance between two consecutive wave crests

Amplitude: The vertical distance between wave crest and wave trough

Frequency: The number of oscillations per unit of time

Next Description of the intangible – wave or particle

Main Natural light

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