Shadow

A shadow is

• An unlit surface ( of an object, such as a wall ), or the means of a light source on their generated projection image of "standing path of light " in the article ( for example, the shadow play ). Their edge is called the shadow boundary or cut-off limit, in astronomy and meteorology also terminator or day - night boundary.

• The unlit space behind an illuminated body.

One can distinguish between different types of shadows depending on the number and extent of the light sources.

• 2.1 umbra
• 2.2 penumbra

• 4.1 Generation of colored shadows
• 4.2 Colored shadows with natural lighting
• 4.3 Colored shadows as pictorial design tool

Shade at an individual light source

Self Shadows

The self-shadowing (also: body shadow ) of a body is the shadow which causes the body to itself by itself. However, only the shadow areas are meant, which are on the respective shadow causing surfaces. In other words, the self-shadowing, the amount of the non-illuminated so that the light source facing away from sides.

A shadow is produced behind an object lack of radiation, receiving the object on its side facing the radiation source side. A shadow is always in the direction of the radiation it receives the opposite cast by an object, even if the shadow impinges on any other object.

Shadow

The drop shadow is caused on a bright background, when the object is in front of it lit by a nearly point- shaped light source ( sun, headlights, photo flash). This shadow is remarkably sharp and is, therefore, intensively perceived by the viewer. It forms the object at least partially, and is indicative - just as the body shadow - the direction from which the light comes.

The shadow projection is also known as the silhouette, it shows the outline so the silhouette of the object. Silhouette is also called a drawing created by tracing the shadow projection. In the shadow theater, the magnification of the shadow to alter the apparent proportions of two objects can be exploited to each other in that they are positioned differently close to the light source.

A negative aspect is this shadow effect associated with very strong exposure events, such as those caused by the atomic flash. The enormous density of radiation causes thermal material changes in the non-shaded area, making the little shadow irradiated surface leaves a contrast as a permanent figure.

Shadows in Descriptive Geometry

In the Descriptive Geometry using shadows of spatial objects ( house, tower, bridge, ...) to make pictures more attractive or to recognize lighting problems in the planning phase. Shade structures for shade from parallel ( sun) or central (lamp) light on a horizontal plane are relatively simple in both parallel projections as well as central projections. Complicated cases it leaves the computer today.

Shadows in extensive or more light sources

Umbra

The core shadow ( umber ) is the space behind the illuminated object is illuminated by any light source.

Since real light sources are not point-like, but have a certain spatial extent, the outlines of a shadow are not sharply defined. The reason for this is that the edge of the shadow parts of the light source are indeed hidden, other areas of the light source, however, are still visible ( penumbra ). If the light source is small enough or far enough away so there is inside of the shade an area in which the light source is completely obscured. This area is the umbra.

In the lunar eclipse the umbra of the earth causes the significant obscuration of the lunar surface, while the effect of the penumbra is visible to the naked eye virtually undetectable. At solar eclipses we experience a total solar eclipse, when you are in the umbra of the moon. In the penumbra can be experienced only a partial eclipse or an annular eclipse. In the latter case, the core does not reach the shadow of the earth.

Penumbra

The penumbra ( penumbra ) is the space behind an illuminated object that is not illuminated by any light sources from the environment. A single point light source can therefore cause no penumbra behind a shadow-casting object. Only the existence of at least a second point source can therefore generate an umbra and penumbra around maximum number of areas, such as light sources are present.

However, the most common cause of penumbra are extended light sources. If about a frosted lamp for illuminating a space used, it can be in the shadow of a body on the wall a nearly black shadow area and around recognize a penumbra area. If one were to look at the area of the umbra in the direction of the light source, so it would be completely covered by the subject matter. The light source is, however, only partially covered from the penumbra out. The dark portion of the core shadow is more extensive and more sharply limited, the closer the object on the wall. With increasing distance of the object from the wall of the umbra disappears and only partial shade it remain.

A hole gets a light shade in the shape of the light source when the hole forms a smaller solid angle as the light source. This can be observed in the nature of circular images of the sun under the trees - even if the gaps in the roof sheets have a square shape, the spots are round. This " shimmer " or " Sonnentaler " change at a partial solar eclipse their form of roundish spots curved sickles. The effect is later on in perfected form at the Camera Obscura.

One of the earliest artistic representations of core and penumbra can be found in Robert Campin (paintings of the " mercy seat ", Stadel, Frankfurt, ca 1410-30 ).

In horticulture is meant by semi shade, when a plant is not directly exposed to the sun. So there is the main driving time April and May light shade, in summer may shade tree for half a day, in the late autumn back light shade.

Shadow by light sources

Sun, moon and lightning in thunderstorms at night can produce visible shadows. Artificial light sources such as lamps, light bulbs, car lights or candles also produce highly visible shadows. Shadow can be seen but only if the light source is so strong that outside the shadow nor reflection of light can be perceived. Stars are so faint that they do not produce visible shadows. Even Sirius, the brightest star in the sky is not bright enough to produce a shadow. It is sometimes speculated that Venus is bright enough to produce a visible shadow. This could actually - be possible - under special circumstances. Who migrates to the period of greatest brightness Venus on a cloudless, clear moonless night away from all artificial light sources with perfectly adapted eyes through a snowy landscape, has a chance to see the shadow generated by the Venus.

Colored shadows

Colored shadows are formed when a scene of at least two different colored illuminated light sources in the penumbra, the successive each illuminated objects and throw it on the back or background of the scene. They can also be produced with a single monochromatic light source and a colored transparent article, such as a colored glass.

Producing colored shadows

By controlled use of different colored light sources and correspondingly positioned in the scene objects can be on a projection screen colored shadows produce experimentally. The perceived mixed colors follow here the laws of additive color mixing.

Colored shadows with natural lighting

Where natural lighting occur in the penumbra area interactions with the generated by subtractive color mixing natural color ( for example, the paint color) of the background on:

When illuminated with natural light, the shadow is not completely dark, but brightened by scattered light from the sky blue. This is compared to the primary sunlight spectrally blue-shifted ( Rayleigh scattering), so the shadow areas included in the same color space more blue compared to the areas that are in direct sunlight. This is particularly clear in the case of diffusely reflecting surfaces, such as a (colored) stucco house wall or a (pure white ) snow surface.

Goethe devotes his color theory intensively with these natural colored shadows, looking for reasons why they (even after observations of Horace - Bénédict de Saussure ) are not always bluish.

Colored shadows as pictorial design tool

Close observation of the color nuances in colored shadows and other effects of atmospheric optics was and is the starting point for the development of important artistic style agents, especially in Impressionism. The representation of the interaction of the pictured object and space surrounding atmosphere creates an image space, which gives the observer into account and the images direct liveliness and freshness.

Aid

A Horizontoskop is a fast and easy tools to identify locally can, what times of day and seasons throw obstacles at one point a shadow.