I was seeing these promo spots by Shell Oil about some whiz-bang light where they had donated a bunch to help poor folks in Africa. Showed up on several channels. Cynical Me thought “Yeah, they probably spend $5000 on the lights and $500,000 on the promo spots”. But it was an interesting gizmo.
You have a clockwork like in a Grandfather Clock, and a bag of rocks. The Gravity Light. Haul the rocks up, then over 20 minutes or so they slowly descend generating enough electricity to power an LED light that was, supposedly, the same illumination as you get from a kerosene lamp. The goal being to “eliminate all the bad” things from using kerosene lamps. They asserted that 1/10 Watt was FINE for that. I doubted. My smallest LED in use is a 7 Watt. This thing must be about the same as a night light, I thought.
Now the worst “bad” thing from kerosene is just the cost to the very poor folks of the world. When you make $3 a day, spending $1 of it for a quart of kerosene to have light is a Very Big Deal. Not so important in the 1st World.
My bias is that I love all things lit on fire for lighting. I’ve got at least 1/2 dozen different kerosene lamps and lanterns that I’ve collected (and used) over the years. Supposedly for “emergencies”, but these days the 1/2 dozen mag lights with D cells and LED bulbs are way more than enough, and the 3 inverters to plug into cars can power way more than that. So really, they have become decorative reminders of 40 years ago when they were important emergency light sources. Somewhere down in my soul I could not believe that a 1/10 Watt, a deciwatt, could possible be all that my beloved kerosene lamps gave me. So I went looking.
GravityLight is installed to provide a 6ft/ 1.8m drop of a 12kg weight. This weight is lifted by a person pulling the orange cord. A pulley system means the weight only feels like 3kg. Once lifted, the weight then falls very slowly (about 1mm / second).
This movement powers a drive sprocket, which rotates very slowly with high torque (turning force). A polymer gear train running through the product turns this input into a high-speed, low-torque output that drives a DC generator at 1600 rotations per minute.
This generates about a tenth of a watt to power the onboard LED and two SatLight LEDs. Together these produce a light more than 5 times brighter than a typical open-wick kerosene lamp.
Once the weighted bag reaches the floor (after 20 minutes), it is simply lifted to repeat the process.
You can have one light, or plug in a couple of “satellite” LEDs that are on outrigger wires.
Their “buy” link points USA folks to Amazon, Walmart, and BestBuy, so not just available in 3rd world countries.
GL02 weight (empty bag) 1.2 kg / 2.6 lbs GL02HS Boxed weight 1.75 kg / 3.85 lbs GL02HS Box dimensions 280 x 223 x 153 mm Master carton dimensions (4 boxes) 455 x 310 x 280 mm Max loaded bag weight 12.5 kg / 27.5 lbs Nominal Voltage* 2.7 V DC Max current* 0.031 A Max electrical power* 0.085 W Luminous flux 15 lm Luminous efficiency 208 lm/W Colour temperature 5000 K Colour Rendering Index > 70 Beam angle 147° IP rating IP2X
So 208 lm/w but only 15 lumens. Color is a bit hot at 5000 k so “daylight blue”. Going to keep people awake at night as that will stimulate the suprachiasmatic nucleus a bit too much, then again, maybe the light level is low enough to not have too much effect. I still like 2700 K to 3600 K better at night.
Color rendering index is only 70, so things will be a bit “off” in color. OK I guess. 80 to 85 is generally “good enough” for fluorescent bulbs. I like the 90+ from incandescents and photo lighting best.
Shipping weight of 1.75 kg isn’t bad at all. (Rocks you get separately ;-)
But back at my Kerosene Lamp… Just how many lumens does it produce?
Oil lamp output in candlepower (CP), lumens and incandescent electric watts equivalent Flat-wick width Candlepower Lumens Watts 3/8" 4 50 3.3 1/2" 7 88 5.9 5/8" 9 113 7.5 3/4" 10 125 8.3 7/8"–1" 12 151 10.1 1-1/2" 20 251 16.7 2× 1", 1-1/16", 1-1/8" 30 377 25 2× 1-1/2" 50 628.5 42 1-1/4" round "Dressel Belgian" 67 842 56 1-1/2" round "Rayo" 80 1000 66.6 2-1/2" round "Firelight" or "store" lamp 300 3771 251
So a small lamp makes 50 to 100 lumens.
Well 15 lm is well below 50 lm. I’m left to assume their 147 degree beam angle gives the same lm / sq-m at viewing distance as a kerosene lantern with 360 degree “beam” angle.
So a good task light, but not a good area light. Still, it could have uses in an emergency kit or a hut in Africa.
Personally, I’d still rather fire up my 3/4 inch wick lamp and put it on the coffee table during a storm driven power outage and get 125 lm over the whole area (plus some welcome heating). But having something for when the kerosene runs out could also be helpful. Having a more blue task light for working on things on a table could also be of benefit.
It also lists 0.085 Watts as the max, but that is without the satellite bulbs. So it looks like the “deciwatt” is about accurate. Using:
To calculate the actual luminous efficiency to get 1 deciwatt as the power drain gives 150 lm/Watt. Going the other way, using their 208 lm/Watt, gives a 21 lumens number. I’d not be surprised at either as the reality.
But it gets more interesting when you look at the Satellite Packs. The same generator, running the same time, powers multiple bulbs. Is it perhaps the case that the single bulb unit just dumps the excess power? How else to explain multiple bulbs working well?
SatLight Accessory Pack
SatLight is an additonal lamp that can be connected to the main GravityLight unit to
extend lighting. Multiple Satlights can be linked together (recommended max of 4).
So “max of 4”? At 15 lm each? That would make a total of 75 lm (or about a kerosene lamp worth) IFF they do not dim when ganged up to the maximum. If they dim to 10 lm each, that’s a total of 50 lm, and about like a small kerosene lamp. So maybe that’s the angle…
Contents Quantity SatLight 2 Power cable 2 SatLight weight 41 g / 1.45 oz SAP Product Box total weight 282 g / 9.95 oz SAP Product Box dimensions 170 x 116 x 78 mm Nominal Voltage* 2.7 V DC Max current* 0.031 A Max electrical power* 0.085 W Luminous flux 15 lm Luminous efficiency 208 lm/W Colour temperature 5000 K Colour Rendering Index > 70 Beam angle 84o IP rating IP2X Guarantee 12 months (subject to conditions) SatLight power cable Cable length 5 meters Connector type 3.5mm stereo jack
These look like mini-chandlers (hang from the ceiling pointing light down) and have a narrower beam angle.
I can see this all working reasonably well for lighting one room. I also suspect some “sellers puff” hiding in the numbers. My first suspicion is that you can only realistically put 2 satellite lamps on the generator before you are sucking voltage down so much lumens drop significantly. “Max 4” is likely at the point where it’s just too dim to use. There must be a transition between those points… I’d like to see separate specs for generator capacity and lamp demand.
IFF that’s the case, then we’ve got about 45 lm (enough for most things kerosene) and about 1/3 Watt that seems more likely to me. LED “night lights” often run about 1/2 Watt (but likely with poorer lm/Watt and better color temp?) so things are in the range of “reasonable” at that point.
Were I hard core about it, I could figure out the Watts available from 12 kg of rocks dropping 2 meters and see what the max theoretical available might be; but I’m more interested in the “after the generator” number.
Still, having light that’s essentially free and works for as long as you can lift a bag of rocks has some benefits.
I’d buy one to add to my “preparedness packs” were it not that I already have above 2 dozen light sources already ;-) I’d also be more likely to buy one with a 2700 K yellow color than a 5000 K blue, but they are trying to exploit the low light sensitivity of the B&W rod receptors, insomnia be damned…
In any case, it is an interesting product and interesting idea. Then again, Amazon is selling them for $79 and that’s just way too much “soak the rich to support the poor in Africa” for my tastes (or my toy budget). Just sayin’… that buys a LOT of kerosene and lamps. Or a lifetime supply of candles at Ikea…