How do visible light waves work

Light waves across the electromagnetic spectrum behave in similar ways. When a light wave encounters an object, they are either transmitted, reflected, absorbed, refracted, polarized, diffracted, or scattered depending on the composition of the object and the wavelength of the light. Specialized instruments onboard NASA spacecraft and airplanes collect data on how electromagnetic waves behave when they interact with matter.

These data can reveal the physical and chemical composition of matter. Reflection is when incident light incoming light hits an object and bounces off. Very smooth surfaces such as mirrors reflect almost all incident light.

The color of an object is actually the wavelengths of the light reflected while all other wavelengths are absorbed. Color, in this case, refers to the different wavelengths of light in the visible light spectrum perceived by our eyes. The physical and chemical composition of matter determines which wavelength or color is reflected. The instrument measures the time it takes a laser pulse to hit the surface and return. The longer the response time, the farther away the surface and lower the elevation.

A shorter response time means the surface is closer or higher in elevation. In this image of the Moon's southern hemisphere, low elevations are shown as purple and blue, and high elevations are shown in red and brown.

Absorption occurs when photons from incident light hit atoms and molecules and cause them to vibrate. The more an object's molecules move and vibrate, the hotter it becomes.

This heat is then emitted from the object as thermal energy. When a fire burns, chemical energy is released in the form of heat and light. The burning fuel, whether it is grass, wood, oil, or some other combustible material, emits gases that are heated by the enormous chemical energy generated during combustion, making atoms in the gas glow or incandesce. Electrons within the gas atoms are promoted to higher energy levels by the heat, and light is released in the form of photons when the electrons relax to their ground state.

The color of a flame is an indication of the temperature and how much energy is being released. A dull yellow flame is much cooler than a bright blue flame, but even the coolest flame is still very hot at least degrees Celsius. Although tar and rags were employed to produce early torches, the first practical step in controlling fire occurred when the oil lamp was invented.

Early lamps over 15, years old Figure 2 have been discovered, made from rocks and shells, which burned animal fat and plant oils. Before gas lighting was invented, there was a tremendous demand for animal oil. The primary source of this oil was the tallow produced by boiling down fat tissues obtained from sea animals, such as whales and seals. Oil lamps eventually evolved into candles that were formed by casting hardened tallow or beeswax, as illustrated in Figure 2.

Early candles generated quite a bit of smoke, but not much light. Eventually, it was discovered that paraffin wax, when properly cast with an impregnated cloth wick, produced a relatively bright flame without a significant amount of smoke.

During the 19th century, natural gas lighting became widespread throughout many of the major towns and cities of Europe, Asia, and the United States. Early gaslights operated by producing a jet of burning gas a quite dangerous situation , while later models were fitted with a mantle, or fine net of chemically treated fabric, which disperses the flame and emits a much brighter light.

Explore the build-up of static electrical charges between storm clouds and the wet ground during a thunderstorm with this tutorial, which simulates capacitor-like lightning discharges, one of nature's light sources. Early microscopists relied on candles, oil lamps, and natural sunlight to provide illumination for the relatively crude optical systems in their microscopes. These primitive light sources suffered from flickering, uneven illumination, glare, and often were a potential fire hazard.

Today, incandescent high-intensity tungsten-based lamps are the primary light source utilized in modern microscopes and the majority of household lighting systems. Presented in Figure 3 are spectral distribution curves demonstrating the relative amounts of energy versus wavelength for several different sources of white light comprised of a mixture containing all or most of the colors in the visible spectrum.

The red curve represents the relative energy of tungsten light over the entire visible spectrum. As is apparent from examining the figure, the energy of tungsten light increases as wavelength increases. This effect dramatically influences the average color temperature of the resultant light, especially when it is compared to that of natural sunlight and fluorescent light the mercury vapor lamp.

The spectrum represented by a yellow curve profiles the visible light distribution from the natural sunlight spectrum sampled at noon.

Under normal circumstances, sunlight contains the greatest amount of energy, but the curves illustrated in Figure 3 have all been normalized to the tungsten spectrum in order to ease comparison.

The dark blue spectral curve is characteristic of a mercury arc lamp, and exhibits some notable differences from the tungsten and natural sunlight spectra. Several energy peaks are present in the discharge arc lamp spectrum that occur a result of superposed individual line spectra originating from the mercury vapor.

The visible light spectrum produced by a white light emitting diode LED is represented by the green curve in Figure 3. Light emitting diodes are inherently monochromatic devices, with the color being determined by the band gap between various semiconductor materials utilized in diode construction. Red, green, yellow, and blue diodes are common, and extensively employed as indicator lights for computers and other consumer electronics devices, such as radio tuners, television receivers, compact disk players, videocassette recorders, and digital videodisk players.

White light LEDs are fabricated from gallium nitride blue diodes by coating the semiconductor die with a phosphor material, which emits a broad range of visible wavelengths when excited by light emitted from the blue diode. Laser spectra, whether derived from diodes or gas lasers, are characteristically very narrow, often comprising only one or a few specific wavelengths.

An example is illustrated in Figure 3 the cyan curve for a low-current semiconductor diode laser that is useful for a variety of applications, including reading barcodes and tracking optical disk data. Tungsten light sources are commonly termed incandescent , because they radiate light when heated by electrical energy. The filaments of modern light bulbs or lamps are generally composed of tungsten, a metal that is somewhat efficient at radiating light when resistively heated by an electrical current.

Modern incandescent lamps descended from the carbon arc lamps invented by Sir Humphrey Davy, which produce light by a discharge arc formed between two carbon rods or filament electrodes when an electric potential is placed across the electrodes. Ultimately, the carbon arc lamp gave way to the first lamps that utilized carbon filaments contained in an evacuated glass envelope.

Tungsten filaments, pioneered in by William David Coolidge, evaporate much more slowly than cotton-derived carbon fibers when heated in the vacuum of a glass envelope. The filament acts as a simple resistor, and emits a significant amount of light in addition to the heat generated by current flow. Explore how two dissimilar doped semiconductors can be joined into a diode and produce light when a voltage is applied to the junction region between the materials.

That spectrum is typically divided into seven regions in order of decreasing wavelength and increasing energy and frequency. The common designations are radio waves, microwaves, infrared IR , visible light, ultraviolet UV , X-rays and gamma-rays. Perhaps the most important characteristic of visible light is color. Color is both an inherent property of light and an artifact of the human eye.

Objects don't "have" color, according to Glenn Elert, author of the website The Physics Hypertextbook. Rather, they give off light that "appears" to be a color. In other words, Elert writes, color exists only in the mind of the beholder. Our eyes contain specialized cells, called cones, that act as receivers tuned to the wavelengths of this narrow band of the EM spectrum, according to NASA's Mission Science website. Join our community of educators and receive the latest information on National Geographic's resources for you and your students.

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