Even in Off-grid Living, Let There Be Light
As shown in the video linked here, advancements in high-efficiency LEDs have made it possible to bring lighting to places with no electrical power grid. The benefits are both clear and numerous, including eliminating the danger of fire, as well as the lung damage from exhaust smoke of kerosene lamps.
Let’s do a bit of basic physics to determine the weight of an object that would need to be lifted two meters (a bit over 6 feet) off the ground to power a light like that found in a common flashlight for an hour.
The brightness of a common flashlight is 25 lumens, and makes use of an LED of 150 lumens/Watt, so we need 0.17 Watts.
We know that energy (E, in Watt-seconds) = mass (M, in kg) * gravitational acceleration (G, in meters/sec2) * height (H, in meters)
and
Energy (in Watt-seconds) = power (Watts) * time (in seconds)
Substituting, we get MGH = PT, or M = PT/GH. Plugging the numbers, we get (0.17 * 3600) / (9.8 * 2) = ~31 KG or ~69 pounds.
That’s a considerable amount, which is why devices like these make use of like gears or simple torque converters, like those used in grandfather clocks. Torque = force * radius, and the device shown here would reduce the force required by a factor of at least 20, enabling a small child to do the job.
