Tag: light

How Do Light Bulbs Emit Light?
The Key Points at a Glance
- An incandescent light bulb gets its light from a filament that is heated by an electric current.
- The filament is housed inside a glass bulb filled with an inert gas mixture to prevent it from overheating and burning out.
- The incandescent light bulb converts just 5% of the electricity into light, while the other 95% is used to warm the room around it.
An electric current flows through the filament of an incandescent lamp, which is typically a carefully wound tungsten wire, to produce light. Consequently, the filament gives out light (light emission). Its internal composition is shown above. Both the base contact and the foot contact carry electricity to the filament. Filament reaches temperatures during operation range from 4500 to 5400 degrees Fahrenheit (2500 to 3000°C). A specific gas, a noble gas-nitrogen combination, is pumped into the glass bulb around the filament to prevent it from burning out. This is why the light it gives out is orange. A lot more blue light reaches us from the Sun since its surface temperature is roughly 9,900°F (5,500°C).
However, only approximately 5 percent of the electricity fed into an incandescent lamp is turned into light; the other 95 percent is wasted as heat. Depending on its size and construction, an incandescent lamp’s luminous effectiveness may range from roughly 8 lm/W to 20 lm/W. (lm: lumen, unit of luminous flux). General-purpose incandescent light bulbs have a lifespan of roughly 1,000 hours.
Single and double helix filaments
A single tungsten filament (Credit: Moehre1992, Wikimedia Commons, CC BY-SA 3.0)
The tungsten filament of an incandescent light bulb is shown coiled and is occasionally coiled twice to produce a double filament. This is due to two factors:
The full length of the about 0.030 mm diameter tungsten wire, which is around 1.0 m long, must fit within the light bulb.
Keeping the wires as close together as possible so that they heat each other is an effective way to keep the heat created in the wire, which is required to reach the high annealing temperature, from being lost too rapidly to the outside as heat loss.
Melting a wire filament
The chemical interaction between the wire and the oxygen in the air that causes the filament to burn through is called oxidation. There is a necessary minimum temperature for oxidation processes to occur. When the wire of metal begins to glow orange, the temperature has risen over the safe threshold. After then, it “burns” due to rapid oxidation by ambient oxygen.
The same thing occurs when oxygen comes into contact with the tungsten filament of an incandescent light bulb.
Preventative gassing to avoid combustion
The evaporation process on the glow wire. (Credit: Planet-schule)
Pumping the air out of the glass bulb or filling it with a gas that will not react with the filament at these high temperatures is how incandescent light bulbs prevent the filament from oxidizing.
Even if the air is sucked out of the bulb, the hot filament will eventually cause the glass to shatter due to the evaporation of the metal within. Individual atoms may break away from the wire surface at the high temperature of the white-hot filament, which is near the melting point of the wire material. The atoms partly deposit themselves as a black film on the interior of the glass bulb. However, this causes the wire to gradually thin down until it finally snaps. The evaporation process at the glow wire is shown in a picture animation below.
The evaporation of the metal is reduced if a gas of a specific pressure is present surrounding the wire, since this gas prevents the metal atoms from leaving the wire’s surface. These days, inert gases are often used with a little percentage of nitrogen added to increase their pressure (for example, argon with roughly 10% nitrogen).
Lifetime
Luminous efficacy and operational lifetime against voltage
Modern incandescent light bulbs are designed to last for 1000 hours. This is a middle-ground solution since it requires a trade-off between low temperature (lower luminous effectiveness and longer life) and higher temperature (more luminous efficacy and shorter life).
The figure depicts the correlation between an incandescent lamp’s luminous effectiveness (brightness or luminous flux), useful life, and operating voltage. Even a little drop in operating voltage will diminish the lamp’s brightness by a noticeable amount, but it will give you far longer use out of the bulb.
Incandescent light bulb current flow
Upon first activation, an incandescent lamp’s filament can handle a high current since it is cold. However, the wire becomes very hot due to the current flow, which increases the resistance of the filament and slows down the current flow. Therefore, the current is much lower while the device is running compared to when it is first turned on. Because of this, an incandescent light bulb cannot be considered an OHM resistor.
Halogen lamps
A halogen light with a dimmable low voltage bulb.
An improvement upon the incandescent light, the halogen lamp (above) uses a tungsten filament and a filling gas that includes a halogen component (halogens are iodine, bromine chlorine, etc.). The little glass bulb can be built out of either quartz or tempered glass. Halogen incandescent lights with iodine were introduced in 1958.
Chemically less aggressive and colorless bromine compounds like bromomethane (CH₃Br) were developed later, enabling machine manufacture. At lower temperatures near the bulb, the bromine produced from the bromine compound combines with the tungsten atoms evaporating off the filament during operation. Even at temperatures in excess of 480°F (250°C) within the bulb, the tungsten bromide does not settle on the bulb’s wall and instead stays in gaseous form.
This is why the size of the glass bulb is restricted. Close to the filament, the tungsten complex breaks down into atomic tungsten, which binds to the hottest (and hence thinnest) sections of the tungsten wire, and bromine, which recombined to produce bromomethane. Regenerating the filament at its weak areas and preventing bulb blackening from tungsten deposits are also byproducts of this cyclical operation.
As a consequence, greater filament temperatures may be used than in conventional incandescent lights, leading to greater luminous efficacies. Despite their compact size and constant high light output, halogen bulbs have a relatively long lifespan.
Readiness for comprehension
The lifespan and light output of a 90% efficient incandescent bulb.
An overhead projector’s controls often include an “economy” and “brightness” switch. Comparing the economy circuit’s 90% operating voltage to that of the typical bright circuit’s 100% operating voltage reveals that the former is much more efficient.
Using, we can find out how much longer the lamp lasts and how much the luminous effectiveness drops as a consequence of this.
The lamp’s useful life is increased by a little over 400% when the operating voltage is decreased by 10%. As a result, the bulbs’ lifespan is increased by more than a factor of four.
In contrast, the luminous effectiveness (brightness or luminous flux) only decreases to about 70%. It’s been cut by around a third as a result.
November 28, 2022
History of Physics: From Antiquity to Modern Times
October 7, 2022
Christiaan Huygens: Founder of the Wave Theory of Light and First Pendulum Clocks
Christiaan Huygens, also known as Christianus Hugenius, was a Dutch astronomer, mathematician, and physicist who was born (April 14, 1629) and died (July 8, 1695) in The Hague. Huygens is widely regarded as one of the most accomplished scientists and mathematicians of the 17th century, despite the fact that he never used the “infinitesimal calculus” that was established during his lifetime. While studying the effects of elastic impact, he developed a concept of relativity and built the first pendulum clocks, cementing his place in history as the creator of the wave theory of light. He made significant astronomical discoveries using telescopes that he refined.
Christiaan Huygens’ Origin and Education
Christiaan Huygens (1629-1695).
Huygens was born the son of Constantijn Huygens, who was a linguist, diplomat, composer, and the leading poet in Holland at the time. Christiaan’s early exposure to famous people like Rembrandt, Peter Paul Rubens, and René Descartes was made possible by his father’s extensive network. Throughout Christiaan’s childhood, he received instruction from his father. Later, he attended the University of Leiden to study law, but he quickly shifted his focus to the “hard sciences” instead.
In 1651, he published his first paper on the squaring of cones in which he demonstrated a flaw in a supposed proof of the squaring of the circle. In addition, he tackled the π (pi), worked on logarithms, and laid the groundwork for the infinitesimal calculus, which was later developed by Gottfried Leibniz and Isaac Newton.
One of the earliest works on probability theory, De ludo aleae (Dice Theory) was published under his name in 1657. This was preceded by correspondence between Blaise Pascal and Pierre de Fermat, the contents of which, however, Huygens claimed to know nothing about. Examining the answers to the five questions at the conclusion of his book suggests that he was conversant with Pascal’s theories but unfamiliar with Fermat’s combinatorial techniques.
Turning to the Natural Sciences
Huygens’s aerial telescope from Astroscopia Compendiaria tubi optici molimine liberata (1684).
Telescopes piqued Huygens’ interest in natural science, optics, and astronomy, all cutting-edge disciplines at the time. He spoke with Antoni Van Leeuwenhoek, the preeminent microscope lens grinder and designer of his day. Huygens briefly studied microscopic items as well.
His first telescope was built with the help of his brother, Constantijn Huygens Junior. However, he soon started grinding lenses for telescopes on his own. As a result of his work on the wave theory of light, Huygens was able to grind lenses with fewer aberrations and create more precise telescopes; his findings also contributed to an improvement in picture clarity for the camera obscura and the magic lantern. Huygens’ Principle, which was named after him, was the foundation of wave optics. Huygens, like many other scientists of his day, postulated the existence of an aether that both light and gravity traveled through.
Huygens’s explanation for the aspects of Saturn, Systema Saturnium (1659).
Titan, a moon of Saturn, was first spotted by Huygens in 1655 with his homemade telescope. As a result, Saturn joined Jupiter as the only other planet except Earth with a detectable moon (Galileo Galilei had already discovered the four largest moons of Jupiter in 1610). In addition, because of to the enhanced clarity of his telescope, he was able to confirm that what Galileo had mistakenly labeled Saturn’s “ears” were, in reality, the planet’s rings.
Drawing of Saturn, made by Christiaan Huygens. Credit: Leiden University Library.
The inexplicable disappearance of the rings every 14 years, Huygens discovered, was owing to the fact that they were then viewed precisely from the side, but were too thin to be seen from Earth, proving that the rings had no connection to the planet.
Huygens also resolved the brightest portion of the Orion Nebula as an extended luminous zone, and he discovered the rotational motion of Mars and calculated the rotation period (Martian day) at roughly 24 hours. The Huygens Region is another name for this area. He proposed that Venus was shrouded in clouds and identified many nebulas and double star systems. The fifth largest impact crater on Mars also bears his name (Huygens Crater).
Mechanics, Pendulum Clocks and Exoplanets
Christiaan Huygens constructed one of the earliest pendulum clocks, and his book on the pendulum, Horologium Oscillatorium, published in 1673, is on display in the Museum Boerhaave in Leiden, Netherlands.
Huygens’s passions extended beyond astronomy to include mechanics. He worked on the law of inertia and centrifugal forces, and he developed the laws of impact. With the knowledge he gained from studying oscillations and pendulum motions, Huygens was able to create accurate pendulum clocks. Even though he never really constructed it, Galileo had indeed planned a clock like that. However, Huygens was able to submit a patent application for his timepiece. Salomon Coster’s clocks, which he commissioned, were more accurate to within 10 seconds each day; this was a level of precision that wasn’t matched for another century. Subsequently, he built pocket timepieces that used hairsprings and balancing wheels.
Using the knowledge that the evolute of a cycloid is again a cycloid, Christiaan Huygens was able to publish a very precise pendulum clock using a cycloidal pendulum in his work Horologium Oscillatorium in 1673. However, the benefit of improved precision in his design was outweighed by the drawback of bigger friction.
Traité de la lumière (1690).
Even more recently, Huygens was identified as the creator of the first known clock for estimating longitude, which included numerous ground-breaking approaches. In 1690, Huygens published his last scientific work, in which he theorized that extrasolar planets and life may be commonplace in the cosmos.
The accurate derivation of the principles of elastic impact, using a principle of relativity, can also be traced back to Huygens (Galilean transformation). Published in 1669 (in Philosophical Transactions of the Royal Society), and posthumously published in 1703 (in De Motu Corporum), his findings date back to the 1650s and rectify the incorrect approach of René Descartes.
In June 1663, the Royal Society welcomed its first two scientists from outside of England: Christiaan Huygens and Samuel Sorbière (1617-1671). When the French Academy of Sciences was established in 1666, Huygens was named its first director. The great Isaac Newton proclaimed him the most graceful mathematician of his day.
Huygens’ Work in Probability Theory
Christiaan Huygens made substantial contributions to the field of probability theory, a branch of mathematics that deals with uncertainty and randomness. In 1657, he published “De ratiociniis in ludo aleae” (On the Calculations in Games of Chance), which laid the foundation for modern probability theory. In this work, he introduced the concept of mathematical expectation and used it to solve various problems related to games of chance, such as dice games and gambling. Huygens’ pioneering work in probability theory provided a rigorous mathematical framework for understanding randomness and has applications in fields ranging from statistics to finance.
Acoustic
Huygens found the correlation between the speed of sound, the length of a pipe, and its pitch. He worked hard on mid-tone tuning, and in 1691 he figured out how to split the octave into 31 equal steps to correct the Pythagorean comma error in the tonal system of music.
Retirement
Huygens’ health worsened in the 1680s, and he stopped leaving his home as regularly. Christiaan Huygens spent the final years of his life studying the field of music theory. Christiaan Huygens died at The Hague in 1695, single and childless.
Christiaan Huygens’ Writings
- 1650 – De Iis Quae Liquido Supernatant (about pieces floating over liquids). (Link)
- 1651 – Theoremata de Quadratura Hyperboles, Ellipsis et Circuli. (Link)
- 1654 – De Circuli Magnitudine Inventa. (Link)
- 1654 – Illustrium Quorundam Problematum Constructiones. (Link)
- 1655 – Horologium (about the pendulum clock). (Link)
- 1656 – De Saturni Luna Observatio Nova (Discusses the recent sighting of Saturn’s moon Titan and provides details on its discovery.) (Link)
- 1656 – De Motu Corporum ex Percussione. (Link)
- 1657 – De Ratiociniis in Ludo Aleae). (Link)
- 1659 – Systema Saturnium. (Link)
- 1659 – De vi Centrifuga. (Link)
- 1673 – Horologium Oscillatorium Sive de Motu Pendulorum ad Horologia Aptato Demonstrationes Geometricae. (Link)
- 1684 – Astroscopia Compendiaria Tubi Optici Molimine Liberata. (Link)
- 1685 – Memoriën aengaende het slijpen van glasen tot verrekijckers. (Link)
- 1686 – Old Dutch: Kort onderwijs aengaende het gebruijck der horologiën tot het vinden der lenghten van Oost en West. (Link)
- 1690 – Traité de la Lumière.
- 1690 – Discours de la Cause de la Pesanteur. (Link)
- 1691 – Lettre Touchant le Cycle Harmonique. (Link)
- 1698 – Cosmotheoros.
- 1703 – Opuscula Posthuma with De Motu Corporum ex Percussione and
- Descriptio Automati Planetarii.
- 1724 – Novus Cyclus Harmonicus. (Link)
- 1728 – Christiani Hugenii Zuilichemii, dum viveret Zelhemii Toparchae, Opuscula Posthuma.
Bibliography
1. “Huygens, Christiaan”. Oxford University Press.
2. “Huygens”. Merriam-Webster Dictionary.
3. Hugh Aldersey-Williams. (2020). Dutch Light: Christiaan Huygens and the Making of Science in Europe.
4. Treatise on Light by Christiaan Huygens. Gutenberg.org.
October 5, 2022
How Does Pollution Make Sunsets Prettier?
September 27, 2022
How Do You Cut Objects With Light?
September 21, 2022
How Do Plants Grow Towards Light?
In order for plants to make the most of their leaf photosynthesis, they have developed a variety of strategies. The direction in which light is coming in will determine the direction of growth, just as it does with houseplants that are placed in a sunny window. Because of this, they are able to meet their requirements for energy through photosynthesis to the greatest extent possible. But who or what is directing this movement in plants? How are the real, immobile plants able to angle themselves toward the sun even though they are located in the darkest shadows?
Proteins, stem cells, and phototropism
It is essential for a plant to direct its growth toward sources of available light while it is still in its immature stages. In the absence of light, many seeds are able to germinate and live off of the starch and fat that they have stored within their bodies. The young plants push their way to the surface of the soil by elongating as much as possible and working against gravity, which serves as their primary source of guidance.
They do this by using light-detecting proteins, which enable them to bend in the direction of the light to find the shortest path to the sunlight. Adult plants are also able to sway in the direction of the light that is the most intense because their stem cells extend more on the side of the plant that is not directly exposed to light. The term “phototropism” describes the process of growth in response to a light stimulus.
Auxin is a hormone found in plants that assists in bending
The well-known scientist Charles Darwin provided the very first in-depth description of plant motion in his seminal work titled “The Power of Movement in Plants,” which was published in the year 1880.
In 1937, the Dutch researcher Frits Went suggested that the hormone auxin, which is found in plants, might play a role in the process of bending in response to light. Even though numerous subsequent findings have supported the idea that auxin is involved in this process, there was a lack of evidence that for that for quite some time.
How it works?
Auxin is the factor responsible for the elongation of these cells. Producing and transmitting this plant hormone is the job of the cells that are located near the tip of the plant shoot. After making its way through the route and stopping at a number of relay stations along the way, it eventually arrives at its final destination, which is the cells on the dark side.
Auxin is transported from one cell to the next by a complicated network of proteins that act as exporters and importers. This allows the Auxin to reach its final destination. In the presence of auxin, cell division is prompted, and the stem of the plant grows in the direction of the light.
However, in the absence of the transport proteins, the hormone will be unable to reach its destination. So, what happens when either of these substances is lacking in the body? By inhibiting the export proteins in plants called “PINs,” it is possible to make a plant less sensitive to light.
Plants like this defy the pull of gravity and continue to grow upward regardless of the direction of sunlight. The same can be achieved by inhibiting the enzyme that was responsible for activating these proteins. And phototropism will once again stop functioning properly. Auxin is the substance that gives plants the power to exhibit phototropism, bending and growing towards the light.
September 18, 2022
What Makes Glass Transparent?
September 17, 2022
Are There Triple Rainbows? And How Are They Formed?
- A rainbow is formed when sunlight reflects off raindrops and undergoes refraction and dispersion.
- Double rainbows occur when light is reflected twice within raindrops.
- Triple rainbows are possible and result from three reflections of sunlight inside raindrops, but they are much fainter and rarer.
The rainbow is an amazing natural phenomenon. The conventional pattern of colorful bands results from the fundamental laws of reflection, refraction, and dispersion. And under exceptional circumstances, a double rainbow may be marveled at. How about triple rainbows, though? Can they possibly exist? Moreover, how do they form?
Formation of the Single Rainbow
A primary rainbow. (Image: Earth Science Stack Exchange)
Rainbows are one of the numerous natural beauties that everyone is in love with. When rain is falling, they emerge when sunlight reflects off raindrops. The majority of the color spectrum of light is absorbed by the raindrop, but a small percentage is reflected. Because of the sphere’s shape, the raindrop focuses these reflections at an angle of 138 degrees relative to the Sun. After that, there will be a rainbow seen in this intense beam of light.
When light travels through air and then enters water, a phenomenon known as refraction occurs, which is the bending of light. Every one of the sunlight’s colors is slightly distorted when it passes through water droplets. This phenomenon, known as dispersion, is responsible for the separation of colors in a rainbow.
In the droplets, the various sunlight wavelengths are each refracted a little bit differently. We perceive the normal color bands as a result of the light splitting into its colorful spectral components. The blue band is positioned on the inside and the red band is on the outside because the blue light has a shorter wavelength and is refracted more strongly in the water droplets.
Moving From a Single to Double Rainbow
A second, fainter rainbow arc can be seen beyond the first one; its colors are reversed so that red is on the inside. This is because the light is reflected twice within the droplet before it leaves.
A rainbow always appears facing a certain direction: It is situated at 42 degrees on the side of the sky that is directly opposite the sun. It is difficult to see a rainbow at noon because this antisolar point is hidden below the horizon when the sun is high in the sky.
But sometimes, in addition to the main rainbow, a second, paler secondary arc that resembles a mirror reflection of the first arc can be observed on the outer. This is due to the fact that its color scheme completely contrasts with the main arc’s. Because the secondary arcs cause two reflections of the photons within the droplet. The intensity of this second rainbow is lowered, and the order of the colors is changed as a result of the double reflection.
The Formation of the Triple Rainbow
$triple rainbow formation: Light paths inside droplets. The sequence and angle of a rainbow are determined by surface refraction and the quantity of internal reflections: a regular rainbow on the left, a double rainbow in the center, and a triple rainbow on the right.$
Light paths inside droplets. The sequence and angle of a rainbow are determined by surface refraction and the quantity of internal reflections: a regular rainbow on the left, a double rainbow in the center, and a triple rainbow on the right. (Credit: ISTA)
What about the triple rainbows? A rainbow may also split into two secondary arcs. This has always been recognized as theoretically possible. As a result of the sunlight being reflected three times within the droplet, a third rainbow is created. However, this time, the light beams emerge from the drop facing the sun. Therefore, we need to gaze more intently into the sunlight in order to perceive a triple rainbow.
Typically, a triple rainbow will emerge for a brief period of time when it is 40 degrees from the sun and the clouds are darker. The order of colors in the third rainbow will be just like the primary one.
The tertiary rainbow cannot usually be seen since it is only about fifth as bright as the rainbow’s main arc. It is also too difficult to see the third rainbow because it faces the sunlight. Since just five triple rainbows had been reported to science in the previous 250 years, many scientists had written them off as myths. And it should come as no surprise that the first photographic proof of a triple rainbow did not appear in a scholarly publication until 2011.
We have to be looking at raindrops at an angle of 138 degrees from the direction of the sun, or 42 degrees from the antisolar point, in order to see the arc of a natural rainbow.
Interference Arcs and Mirror Arcs
However, according to climate researchers and specialists, the far more typical occurrences of interference arcs and mirror arcs sometimes could be mistaken with a real third rainbow or triple rainbow.
When sunlight reflects off a water surface, such as a lake, the angle of entrance into the droplets changes, creating a mirror arc. Typically, the main arc and the mirror arc cross.
Contrary to actual secondary arcs, interference arcs are located on the inside of the initial rainbow and run parallel to the main arc. They create a string of successively farther-apart replicas of the initial rainbow, each of which becomes weaker and narrower. They are created by the interference—or the superposition effect—of light rays leaving the drop.
Sources:
1. Gary Waldman, 1983. Introduction to Light: The Physics of Light, Vision, and Color.
2. “Triple Rainbows Exist, Photo Evidence Shows,” 2011. ScienceDaily.
3. American Mathematical Society. The Mathematics of Rainbows.
4. Großmann, Michael; Schmidt, Elmar; Haußmann, Alexander, 2011. “Photographic evidence for the third-order rainbow”. Applied Optics.
September 3, 2022