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The existence of nearly all life on Earth is fueled by light from the Sun. Most autotrophs, such as plants, use the energy of sunlight, combined with carbon dioxide and water, to produce simple sugars—a process known as photosynthesis. These sugars are then used as building-blocks and in other synthetic pathways that allow the organism to grow.
The Sun seen through a light fog. The Sun emits light across the visible spectrum, so its color is white, with a CIE color-space index near (0.3, 0.3), when viewed from space or when the Sun is high in the sky. The Solar radiance per wavelength peaks in the green portion of the spectrum when viewed from space.
Sun glitter is a bright, sparkling light formed when sunlight reflects from water waves. The waves may be caused by natural movement of the water, or by the movement of birds or animals in the water. Even a ripple from a thrown rock will create a momentary glitter. Light reflects from smooth surfaces by specular reflection.
A 22° halo around the Sun, observed over Bretton Woods, New Hampshire, USA on February 13, 2021. A halo (ἅλως; also known as a nimbus, icebow or gloriole) is an optical phenomenon produced by the interaction of light from the Sun or Moon with ice crystals in the atmosphere, resulting in colored or white arcs, rings or spots in the sky. [23]
For example, a light source of 1000 lm at a color temperature of 5800 K would emit approximately 1000/265 = 3.8 W of PAR, which is equivalent to 3.8 × 4.56 = 17.3 μmol/s. For a black-body light source at 5800 K, such as the sun is approximately, a fraction 0.368 of its total emitted radiation is emitted as PAR.
For example, fireflies produce light by this means and boats moving through water can disturb plankton which produce a glowing wake. Certain substances produce light when they are illuminated by more energetic radiation, a process known as fluorescence. Some substances emit light slowly after excitation by more energetic radiation.
Because light specularly reflected from water does not usually reach the viewer, water is usually considered to have a very low albedo in spite of its high reflectivity at high angles of incident light. Note that white caps on waves look white (and have high albedo) because the water is foamed up, so there are many superimposed bubble surfaces ...
[64] [65] This is the opposite of the expected pattern if the Sun, currently closer to the Earth during austral summer, were the principal climate forcing. In particular, the Southern Hemisphere, with more ocean area and less land area, has a lower albedo ("whiteness") and absorbs more light. The Northern Hemisphere, however, has higher ...