Some thermal sources have bright colors due to the presence of certain chemical elements in their composition. When these elements are heated, they emit visible light, creating vivid colors.
When an object is heated, it begins to radiate light. The hotter it is, the more the object emits high-energy light, transitioning from a deep red to a bright yellow, and then to an intense blue-white. This is what we call the phenomenon of black body radiation. A simple example: heated metal changes from dark red to bright white as its temperature increases. The color thus directly depends on the temperature; as the temperature rises, the emitted light shifts towards colors of high energy intensity.
Each material, depending on its chemical composition, emits a characteristic light when heated strongly. For example, sodium produces that typical yellow-orange light of city lamps, while copper turns rather bluish-green when burned. Each element has its own atomic transitions: basically, when it heats up, its electrons make little jumps between different energy levels, emitting a very specific color during the process. This is precisely why, when burning certain particular materials like mineral salts or metals, we can observe beautiful colored flames, ranging from bright red to deep blue.
The level of oxygen during combustion completely modifies the color of the flames. A flame that is well supplied with oxygen usually burns bright blue, a sign of complete combustion where the temperature is quite high. Conversely, when oxygen is lacking, combustion becomes incomplete, producing soot particles, among other things. That's why a flame takes on a rather yellow-orange color in these cases, with those small illuminated carbon particles glowing intensely. The intensity of the fire also plays a role: the more intense and rapid the combustion, the more dazzling and bright the flames will be.
When you increase the pressure or density around a heat source, the particles come closer to each other, multiplying the collisions between them. These more frequent collisions release more energy, thereby changing the observed color. For example, under high pressure, the flames of a combustion can become bluer, indicating a higher temperature. Similarly, a very dense star, like a white dwarf, will become incredibly bright and take on a color very close to white or bright blue. In short: bringing or compressing particles together encourages energy exchanges, which intensifies brightness and significantly alters the visible colors.
When light from a thermal source propagates in the air or passes through mediums like smoke or water vapor, it never travels alone. It can be scattered, absorbed, or even reflected by these various surrounding elements. The greater the quantity, size, or density of these suspended particles, the more the perceived color may change. For example, a red-orange flame seen through dense smoke may shift to a more intense red hue, as the blue or yellow wavelengths are more absorbed or scattered. The environment thus directly influences the final color that the eye perceives.
At high temperatures, even commonly used solid materials such as steel become incandescent. They transition from dark red to bright red, then to orange, yellow, and finally white as they heat up further.
The term "black body" refers to an ideal object that perfectly absorbs all incoming light. Ironically, these ideal black bodies produce thermal radiation whose color depends solely on their temperature, and can therefore be very bright, ranging from dark red to brilliant white!
Fireworks specialists use specific chemical compounds (such as copper, barium, or strontium) to produce the vibrant colors of fireworks; each chemical element emits a characteristic color when burned.
The sun appears to us as white-yellow, but it is actually considered a 'green' star from the perspective of its temperature. It seems white-yellow to us due to the sensitivity of our eyes and the mixture of wavelengths received on Earth.
The increase in pressure or density of a combustible gas usually intensifies the chemical reactions during combustion. This often alters the intensity and sometimes the color of the emitted light, directly affecting the brightness and hue of the flame.
When metals are heated, they emit thermal radiation known as black body radiation. Initially, they appear dark red, then gradually progress through various ranges – bright red, orange, yellow, white – as the temperature increases, following a predictable progression of the visible spectrum.
Yes, generally. The color of thermal light largely depends on its temperature: a lower temperature will emit a deep, warm red, while as the temperature increases, the color transitions to orange, yellow, white, and then a very warm pale blue, thus representing an approximate but accurate correspondence between hue and temperature.
Absolutely. The addition of specific chemical elements (such as copper, sodium, or lithium) can significantly change the color emitted by a flame, which is often used to create spectacular colors in fireworks or other pyrotechnic applications.
The yellow color of a candle comes mainly from the incandescent soot particles produced during incomplete combustion. In contrast, the bright blue of the blowtorch is due to a more complete and efficient combustion, producing very little or no soot, but rather a characteristic blue light emitted by the excitation of gas molecules.
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