I designed this gravity light using a motor from an old microwave oven.
This light will provide enough light to read with for about 5 to 10 minutes depending on the height that the generator is mounted above the floor, the weight used and the individual characteristics of the motor.

An estimated 16 percent of the world's population — 1.2 billion people — have little or no access to electricity:

https://mashable.com/2017/09/15/one-billion-people-dont-have-access-to-electricity/

This is designed as a school project, the skills/knowledge to be gained include:
3D printing
Pulleys
Electricity
Light
Soldering
Tying knots (fishing & others)
Social Science & 3rd world awareness

PERFORMANCE:
Performance varies depending on many things, so using the best of 5 motors that I had tested I measured the performance - using an LX Meter App on my phone, and with the reflector 12 inches (300mm) above the meter and the generator 10ft (3m) above the ground:

Weight - - - LX - - - Time
= = = = = = = = = = = = =
1kg - - - - - 32 - - - - 8:10
1.15kg - - - 45 - - - - 7:45
1.3kg - - - - 62 - - - - 7:00

As you will see in one of the photos, to get the weight of 1.3kg I used a 1 litre water bottle and the 2 magnets from a microwave oven.
What I found was that each motor needs a different weight to get to the point where the LX level suddenly increases. The most efficient motor that I found was the Galanz GAL-5-240-TD.

NON-PRINTABLE PARTS:
1 x turntable (tray) motor either from an old microwave oven OR from the internet (220-240V 4W Synchronous Motor) I have not tried a 110V motor yet. The photos attached show 2 different brands of motor that work and a different brand that does not work.
4 x Silicon diodes (e.g. 1N4148)
2 x 1000uF 63V Electrolytic Capacitors OR 1 x 2200uF 63V
Figure 8 speaker cable OR similar
Braided fishing line for pulley
Thin twine for harness for the water bottle weight using the 2 rings that you print out
Thin twine OR curtain nylon cord to tie frame to the wall
2 x M3 25mm screws
4 x M3 12 mm screws
2 x M3 nuts
M3 washers (optional)
4 small self tappers OR similar to hold the LED in place
1 x small metal (key) ring (optional to join weight to fishing line)
1 x 2 litre (0.5 gallon) plastic container to hold water
1 x LED (50W 12V-36V High Power LED Lamp Light COB SMD Bulb Chip). See photos for LED style.
1 x Curtain OR roller blind chain, the length to suit mounting height (looped is tidier, but slightly more expensive), suggest at least a 1m loop (2m total length) with a ball size of 4.5mm
Aluminium foil (cooking from your kitchen)

TOOLS:
3D printer
Soldering iron
Various hand tools
Light meter OR an App on a Smart Phone (e.g: “Physics Toolbox Sensor Suite”)

NOTES:
Do not pull the left hand side of the curtain chain, as the Tension Post may break.
The assembly needs to be mounted to a wall or other vertical surface, not a horizontal surface.
The LED can be hung from an appropriate point or print the 3D brackets and make a table lamp.
Where the screws are going into the plastic without a nut, they will tap into the PLA plastic to make their own thread, so if the plastic used is very hard it may be best to file a slight point onto the screw tip, or using a Phillips head screwdriver slightly countersink each hole.
Knots:
Reef Knot – for the water bottle harness.
Uni Knot - on each end of the braided fishing line.
Figure 8 – for each end of the cord holding the frame to the wall.

KITS:
My son is keen to make some pocket money, so he is going to provide kits for those that are interested, all you will need is a 3D printer, PLA filament, some aluminum foil from your kitchen, and a suitable (milk/water) container for the weight. The kit will probably cost about $AUS30 to $AUS40 ($US25 to $US35) per kit including shipping. Please let me know if you would like to be notified when they are available.

ASSEMBLY INSTRUCTIONS:
I will write these up over the next few weeks if there is enough interest.

ENHANCEMENTS:
I would be really interested in any enhancements that you make or suggestions that you have.

A challenge is to build a gear box to double the revolutions of the generator in order to either double the duration or double the light intensity depending on whether or not you double the weight.

A very subtle refinements could be to replace the silicon diodes (junction voltage of say 0.6v) with Schottky diodes (junction voltage of say 0.3v) or fast switching diodes, but I don't expect it to make any visible difference.