Gravity-Powered Light

This is pretty interesting! I wonder what goes into the components and if you could rig up a DIY version (that didn't rely on plastic imported from China)...

https://www.lehmans.com/product/gravity-powered-light/

You'll have access to light, anywhere! The GravityLight is a non-electric solution that uses an elevated weight on a pulley system that slowly powers a generator as the weight falls to the ground, providing you with usable light. No batteries or sun needed, just hang it up and fill the bag with rocks or sand (about 26-1/2 lb).

Affordable, safe and eco-friendly!
Provides 20 minutes of light as it descends; just lift for more light
Gives you instant light (15 lumens), no running cost
Since no batteries are used, you can store the light indefinitely - no worries of batteries degrading
When installed, it provides a 6 ft drop of about 26-1/2 lb (12 kg) weight
The pulley system makes it only feel like about 6-1/2 lb (3 kg)

Sweet Tatorman's picture

26.5 lbs dropping 6 ft with 100% efficient conversion to electricity would produce 0.060 Whr. Top quality white LEDs (not likely in most Chinese products but let's give them the benefit of the doubt) can provide efficiencies on the order of 150 lm/W so 15 lumens would require 0.10W. 20 minutes is .333hr so (0.10WX.333hr)=0.0333Whr. This would thus imply a mechanical to electrical conversion efficiency of 0.0333/.060 = 0.555 or 55.5%. This is highly improbable. At these tiny power levels it would be a stretch to achieve even 10%. One or more values in their specification must be bogus. For the listed price of $100 one could by quite a bit of solar panel and battery capacity.

Blueberry's picture

Enjoy the you tube with a cold one https://www.youtube.com/watch?v=0UoERSKi7-Q

I appreciate the feedback - good to know how the math actually works out (or rather, doesn't).

I bought one of these directly from the company because they were offering a subsidy deal such that my purchase enabled them to sell one to someone in the poor world at an affordable price. I was disappointed at first because it is designed to be looped over an exposed rafter so not easily installed in normal drywalled house. Then my husband bought a wall tent as a guest room for summer visitors and we had this really cool light to use in it. No exposed flames and no extension cords needed!
It works great. We timed it at 17.5 minutes (best height gives 20 mins); just enough to give you time to sort through your pack, find your pjs, and get into bed. Another pull gives you a time limited period to read in bed.
I know its not a sustainable technology but as legacy tech it may ease the descent for my grans and great-grans. Win!