Tag: electric

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
Underwater Camera Without Battery or Cable
Using water as a source of energy, scientists in the United States have developed a tiny camera capable of taking photographs underwater without the need for recharging or any other maintenance. The gadget is able to do this because of piezo elements, which transform the energy in water vibrations into electricity, and its low power consumption compared to traditional cameras. It uses a passive method of data transmission in which it backscatters an incoming sound wave.
A very small percentage of the oceans have yet to be surveyed and investigated. There hasn’t been much progress made in this area, even after massive censuses like the Census of Marine Life were conducted. The challenge of putting several sensors and cameras in the water without an external power source is a contributing factor. To date, such equipment has relied on either batteries, which have a finite lifespan, or cables from ships, which can only provide power for a limited duration.
Potential energy from vibrations
The underwater camera’s construction without a battery or cable. (Afzal et al./Nature Communications, CC-BY 4.0)
But now, MIT graduate student Sayed Saad Afzal and his colleagues have developed an underwater camera that doesn’t need any external power source to operate. There are two technologies that work together to make this happen. The first is the use of piezoelectric elements, which can transform mechanical vibrations into electricity. This is achieved by shifting charges in the element generated by the vibrations.
Now, a ship’s horn, a marine mammal’s snort, or even a sonar may cause the water to vibrate and, therefore, strike the piezoelectric transducer, producing electrical energy that can charge a tiny supercapacitor. The camera is powered by this current. Unfortunately, regular color cameras aren’t very power-efficient; therefore, particular consideration was given to this aspect of the design.
Image captured by a monochrome camera sensor
The battery-free camera prototype’s first shots. (Afzal et al./Nature Communications, CC-BY 4.0
The researchers had to be creative to reduce the hardware footprint as much as feasible. Color photos were preferred, but the most cost-effective digital image sensors only create monochrome (black and white) photos. To see anything at all in the dim underwater environment, the camera has to be able to shine a light on its targets, which also demands electricity.
The researchers solved this issue by integrating a black-and-white image sensor with red, green, and blue light-emitting diodes. The sensor takes one picture of an item as each of the three colored LEDs lights up in succession. The three monochrome pictures are distinct from one another because the color elements are absorbed and reflected differently depending on the color of the object. Recombining them using specialized software allows for the recreation of a full-color picture, conceptually analogous to that of an LED television.
Backscattering is used to send information
The data transfer from the underwater camera to the ocean surface was another obstacle that needed to be addressed. The team at MIT employed a method that has already been used in battery-free mobile phones and LED billboards. The new camera uses backscatter technology, which encrypts its data by absorbing or reflecting an acoustic signal aimed at it, rather than actively creating radio waves or other signals to transport the data.
The camera is then radioed by the receiver (which can be a buoy floating on the water’s surface) to the depths below. The zeroes and ones of digital image data are imprinted on the signal by the camera’s piezoelectric module, which reflects the signal back for 0 and absorbs it for 1. The reflected signal can be picked up by the receiver buoy’s submerged microphone and decoded.
A single switch is all that’s needed to toggle between absorption and reflection in this setup. The underwater camera without battery or cable consumes just one-hundred-thousandth of the power required by conventional submerged communication systems.
Successful results from the first round of testing
Initial field testing of the scientists’ new battery-free camera included using it to document the plastic debris lying at the pond’s bottom. High-resolution photographs of a starfish were captured, and the camera also caught the development of the aquatic plant Aponogeton ulvaceus over the course of a week. All of these evaluations were carried out with the prototype camera fully underwater, functioning independently, and without a battery or power cord.
Researchers think that autonomous and low-cost underwater cameras will open up new avenues for studying the ocean. In addition to monitoring fish in aquaculture, they might be used to investigate marine pollution and look at uncommon species. The researchers are already working on increasing the battery-less camera’s storage capacity and range (which is now just 130 feet or 40 meters) so that it can be used in such applications. Source: Nature Communications, 2022; doi: 10.1038/s41467-022-33223-x.
September 27, 2022