Light has become primordial for our life. We are dependent on it since it’s the way we are able to perceive things visually. Without any light, we wouldn’t be able to see anything. Our main source of light lies outside the Earth, on the Sun. Nonetheless, we still managed to create our own light sources to facilitate our lives and be able to see even when the sun is not peeking through the clouds or sky. But, what if one day, we all disappeared from the earth? What would happen to the energy sources, but specifically, what would happen to the light we created? How long would it take for it to disappear as well?
To answer this question, we need to consider every source of light created by human kind.
Diesel Generators
Diesel generators are mechanical-electrical machines that provide energy to many remote communities, such as isolated islands. These generators can operate until the diesel fuel ends, which could occur from days to months, transforming the chemical energy present in the fuel into mechanical energy through the diesel engine.
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Diesel generators are also composed of an electric generator(converts mechanical energy into electrical energy), fuel system (stores and supplies diesel fuel to the diesel engine), cooling system (mantain optimal temperature), and control system(monitors parameters of diesel generator).
Geotermic Plants
Geotermic plants do not require fuel provided by humans since they obtain their energy from the temperature inside the Earth.
Nonetheless, geotermic plants cannot function without maintenance forever. As an example, the geotermic plant of Svartsengi Island in Iceland has a maintenance manual that explains that, every six months, the operators need to change the gearbox and oil all electric motors and couplings.Consequently, if humans disappeared, all these required maintenances would be impossible to do, and, eventually, geothermic plants would succumb to corrosion.
Wind Turbines
The structure of wind turbines was designed to avoid constant maintenance by individuals since there are many of them and it would be very laborious to climb every time.
The wind turbine of Gedser, for instance, in Denmark, was installed around the late 1950s and generated power for 11 years without maintenance.
However, nowadays, wind turbines are designed to be able to function for 3 years without any human intervention. For that reason, wind turbines would eventually stop functioning due to lack of maintenance and, probably, because their gearboxes would crash.
Hydroelectric dams
Another infrastructure that provides electrical energy for light are the hydroelectric dams, which would, if humans disappeared, most likely succumb due to clogged intakes or some sort of mechanical failure due to lack of maintenance.
Hydroelectric dams are able to generate electricity from the movement of water, therefore, the energy available will depend on the volume of the water flow and the elevation of the infraestructure. If there is more elevation and flow, then its possible to generate more energy.
It’s important to clarify that dams are only a part of a hydroelectric facility, being the component that transforms potential and kinetic energy from the water into electrical energy through a turbine and generator. Often dams are designed to create reservoirs of water that will later flow through the turbines.
Batteries
All light sources that are fueled by batteries would stop functioning after a decade or two. Even if these batteries don’t spend their energy (which would be the most probable case since humans are no longer on Earth to use these lights), they would eventually self-discharge.
Nevertheless, there is a exception located in the Clarendon Laboratory at Oxford University, where there is a bell that rings so low that is barely noticeable so it only uses a little of its energy, yet it has been ringing since 1840. But there is a problem, which is that we don’t know what exact type of battery it uses since no one wants to dismantle it.
Unfortunately, since there is no light attached to the bell, this example wouldn’t be useful for our question.
Nuclear reactors
On the other hand, nuclear reactors, in theory, could keep functioning indefinitely if they don’t abuse their energy. Anyhow, there is a trick: even if there is enough fuel, nuclear reactors wouldn’t be working for long periods of time since the moment there is a malfunctioning, the core would stop working immediately. This is caused because of reactor’s design in order to avoid any incidents so, the moment a fault is detected, the machine will stop functioning.
Respecting its functioning, nuclear reactors create nuclear fissions (atomic nucleus splits into smaller fragments). Once this occurs, the smaller atoms release an average of two to three neutrons which may cause new nuclear fissions, creating more neutrons and, consequently, creating a chain reaction. Usually, this process is created by clashing uranium-235 or plutonium-239 with neutrons, creating a chain reaction of nuclear fission that releases a great amount of energy as heat.
235U + n → 236U → Fission Products + 2-3 neutrons + Energy 239Pu + n → 240Pu → Fission Products + 2-3 neutrons + Energy
Space Rover
Space probes and robots would be the machines that most time would endure without humans, lasting millions of years.
As an example, there is a robot named Curiosity which was released onto the space, landing on Mars. The energy obtained for its functioning comes from the hear released by the sun, which the robot absorbs through a chunk of plutonium in the end of a stick.
Of course, eventually, Cursiosity's voltage would drop too low to keep working, yet before that all the parts that compose it would most likely wear out.
This rover does have lights, yet not common ones. These lights are only activated when the rover makes any type of measurement. This is because, if there is no human on board, spacecraft has no necessity to contain lighting.