Reflected light, Iridescence, and refracted light ( interference ) are ways in which colors are made visible to the eye. Creatures only see light in the wavelengths visible to their unique eye structure. A rainbow represents the light spectrum which results from the sun striking raindrops ( or other prisms such as quartz ) and having its wavelengths bent, or refracted so that colors are made visible. These are the colors the human eye can see. There are more colors- such as ultraviolet or infrared which are only visible to creatures possessing eyes that are able to see these colors. Bees and some other insects see ultraviolet and are attracted to certain flowers by ultraviolet “ nectar guides” which lead the insect into the flowers far enough to ensure pollen pick- up or transference. Nature, of which we are a part, is full of the effects of sunlight striking objects and the colors that result are formed by what happens afterwards.
Light travels in a straight line until it strikes something. When light hits an object it gets reflected, or bounced off, in different directions. Colors occur because light, composed of a broad spectrum of wavelengths will reflect and scatter differently after striking different objects. Some substances absorb certain wavelengths while the rest are then scattered.
One of the effects of light scattering through the atmosphere has given rise to the saying “ red sky at night, sailor’s delight, red sky in morning, sailors take warning.” This is because weather systems generally move from west to east in the middle latitudes because the prevailing winds are westerlies. As rays of sunlight are pass through the atmosphere, they split into colors of the spectrum as they ricochet off water vapor and dust particles. The amounts of these particles determine what colors we see in the sky, and they can be useful indicators as to weather conditions.
If we see a red sky at night, it implies the setting sun in the west is shining on clouds or particles of dust and water vapor to the east and atmospheric conditions to the west are clear ( or else you would not see the sun setting ). The sky appears redder if you can actually see the sun setting. As the sun still shines from the west, clouds that have broken up and moved east are still being shined upon by the setting sun, even after both the clouds and the sun may have disappeared from sight. Red light still breaks through the atmosphere while the shorter wavelengths will scatter and break up. Usually this indicates high pressure with its stable air is coming from the west and fair weather should follow.
Red sky in the morning often indicates that a high pressure system has passed through and a low pressure system storm system may be moving in from the west. If the color of a morning sky is a deep, blazing red, it can indicate high water content exists in the atmosphere and rain may be on the way.
Another way we see colors is through light reflected off pigments of objects. Grass appears green because chlorophyll in cells absorbs all colors except green, which is reflected as the sun’s rays hit the leaf surfaces. Amounts of chlorophyll in different species of plants are different and produce deeper, darker or lighter greens accordingly. Pigments are colors that last and are not affected by turning an object at different angles. Colors are produced by the selective absorption and reflection of specific light wavelengths. A green caterpillar looks green at all times if struck by light because certain wavelengths of light are absorbed, while green wavelengths are reflected and made visible to an observer. Usually only the outermost cells of an organism have pigments which produce the constant colors of species.
In contrast to colors produced by pigments, structural colors are created by the physical interaction of light with the intrinsic characteristics of structures within an organism. Iridescence is a type of structural color that is especially found in certain beetles and butterflies. Incoming light strikes many layers of plates or scales which results in multiple instances of constructive interference where light is reflected many times and produces vibrant and intense colors. Metallic colors in some beetles, such as Bupestrids and some Cicindela and others , plus the iridescence colors of many butterflies are the result of structural interference of incoming light. These insects also have pigments that produce constant colors. But light interference produces colors that can change as the viewpoint of the observer or the insect changes. Or if the butterfly or beetle move into a shaded area, or it gets cloudy, iridescence is affected temporarily. This can make photographing insects exhibiting structural colors a vexing enterprise, frequently requiring patience and a lot of moving around as the insect moves to areas of different lighting. Full sun produces the most striking and clear colors and edges, so sunny days are optimal for seeing the best iridescent colors.
Some plants have brilliant, shiny fruits that have an inner geometry of films and pockets that make for an aesthetically pleasing color that can last sometimes for many months, Winterberry maintains its bright red coloration throughout the winter, making it a vibrant contrast to white snow that may stick to its branches. It is highly visible to any wildlife that may need its fruits for survival.
Birds have feathers than produce colors both by pigments or by light refraction caused by the structure of the feathers. Feather color may be the result of either or both. The throat of the male Ruby- throated hummingbird refracts light like a prism which results from the structure of the feathers splitting light into the rich ruby color. Depending on the angle of the viewer, the throat can appear black or an iridescent ruby red. Sometimes tiny air pockets in the barbs of feathers will scatter incoming light that produces a blue color, like that of a blue jay or indigo bunting. Backlight the same feathers, and they look brown because of melanin in the feathers.
This is just the tip of the iceberg, a mere reflection and consideration of how color is produced in nature. We can all be backyard scientists if we slow down and observe our natural surroundings, of which color just one primary part of the composition. Even in the winter gloom, there are vibrant sunsets and other splashes of heartening colors in the landscape that can cheer us up, if just for a moment.
Pamm Cooper all pictures copyright 2014 by Pamm Cooper