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Shadows are created when something blocks the path of light rays that would otherwise reach a surface. Some things are transparent (like windows), while others don’t block any light at all (like rain).
Generally, the shadow area is the region in a light beam that receives the least amount of illumination. This dimmer zone tends to take on the shape of the opaque object that is obstructing or redirecting the beam.
What Makes a Shadow?
Shadows are dark areas that appear when light rays are blocked by an object. This can be a person, an animal or something else.
Generally, an opaque material blocks all of the rays of light. A transparent object lets some of the rays pass through it and does not make a shadow.
The center part of the shadow, where no light reaches, is called the umbra. The edges of the shadow, where the rays can reach, are called the penumbra.
The shape of the object and the angle at which the light hits it determine the size and shape of the shadow. For example, an object blocking more light at a lower angle makes a longer shadow than an object blocking more light at a higher angle.
The Brightness of the Light
The brightness of a light source, or the amount of visible light it emits, is measured in lumens. This is similar to measuring the wattage of a light bulb.
The lux (pronounced LUX) readings you get when measuring the brightness of a light source with a lux meter will vary significantly with distance. This is because a mathematical relationship known as the inverse square law governs the brightness of a light source at different distances from it.
This is why when a light beam goes past a fire, it must be brighter than the light produced by the flames. Otherwise, the light from the fire will fill in any dim area created by the other light beam.
This is because light beams can not directly interact with each other, since each is made of quantum particles called photons. They cannot directly absorb, deflect, or bounce off each other because photons do not carry any electric charge or magnetic moment.
The Density of the Air
The density of the air depends on a variety of factors. Specifically, the temperature and pressure of the air affect it.
Density can also change as a result of changes in altitude. For example, the air at Denver is less dense than Miami.
This decreases the drag on an airplane. It causes it to fly slower, and loses power or lift on its wings or rotor.
In addition to changing altitude, air density can be affected by the amount of moisture in the air. The more water vapor in the air, the less dense it is.
The density of air is denoted by the Greek letter r (rho). It measures the mass per unit volume of air.
Unlike air which is transparent, smoke is rich in solid particles that can block some of the light. The resulting dimmer region of the light beam is called a shadow.
To see a shadow, the beam of light must be about as bright or brighter than the light coming from the fire. Otherwise, the light from the fire will overpower and fill in any dim region created by the shadow.
The refraction of light, which occurs at the interface of deflection between two different materials, is another important factor in creating a shadow. It is a function of the heated air and certain pollutants in the flames, causing them to deflect some of the light inside the flames.
The soot that is produced in the burning process can also play a role in forming shadows. It absorbs some of the light, so that the shadows it produces appear like dancing waves.