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The device does not use a typical consumer LED lamp. The efficiency of its LED lamp is about 210 lm/W whereas for an average consumer lamp it is less than 100

The device does not use a typical consumer LED lamp. The efficiency of its LED lamp is about 210 lm/W whereas for an average consumer lamp it is less than 100 lm/W. More important is that the brightness of this LED is just 16 lumens compared to 400 lumens for the average consumer lamp. The device itself only generates 0.075W. This is well within your potential energy calculations. While this is not the same level of brightness that westerners are used to, it is sufficient for reading and other activities. The device has an extension point to attach a cable to task-specific spotlights, used for reading for example. Or to power a radio. Tech Specs: http://gravitylight.org/techspecs http://gravitylight.org/techspecs

yongjik 10y ago
So, according to the tech spec, it has 0.075 W output = 75 mW. A single 1.5V AA alkaline battery can provide the same output (50 mA * 1.5V = 75 mW), and it can provide up to 2600 mAh, which equals 52 hours, or almost a month if you need the light on for two hours every day. So a family can simply buy a (very small) LED light and a single rechargeable AA battery. They probably could find a shop to recharge the battery once every month, with minimal fee. Sounds much more reasonable than buying a 12.5kg pulley that needs to be reset every 20 minutes. * The fact that I've never heard of these amazing "single AA battery powered lights" sweeping through African homes makes me doubt your claim that it's "sufficient for reading and other activities". (Many Africans have cell phones; many more should be able to afford an AA battery.)
- infodroid 10y ago
  The problem is that the cheapest source of lighting for many poor communities is hazardous biomass fuels like kerosene. And unfortunately good alternatives like solar may not be a viable option for everybody. Sure there are many parts of Africa with good infrastructure, but just because you are living in Africa in the 21st century does not mean you are now surrounded by power lines! The nearest power socket might be a few dozen or even hundreds of miles away. How are you going to get there and back? If you don't succeed in charging your battery today because of floods or storms, will you go without lighting? And there is also cost and access to credit to account for. The GravityLight is targeting $5 price point, whereas a basic solar charging pack in Uganda costs approximately $150 USD on finance [1]. Compared to batteries, GravityLight has no operating costs. It also does not degrade over time, lose charge when it is unused, or unexpectedly stop working when the battery runs out. This might be an important consideration for some. As for whether the device can produce adequate lighting. A candle or simple kerosene wick lamp will produce around 8 lumens of light output [2] compared with the 16 lumens of the GravityLight. So this is pretty good. Each community has different needs and circumstances. Providing people with more alternatives to kerosene fuel will allow them to choose the solution that is right for them. [1] http://www.fenixintl.com/uganda/ http://www.fenixintl.com/uganda/ [2] http://evanmills.lbl.gov/pubs/pdf/offgrid-lighting.pdf http://evanmills.lbl.gov/pubs/pdf/offgrid-lighting.pdf

yongjik 10y ago

So, according to the tech spec, it has 0.075 W output = 75 mW. A single 1.5V AA alkaline battery can provide the same output (50 mA * 1.5V = 75 mW), and it can provide up to 2600 mAh, which equals 52 hours, or almost a month if you need the light on for two hours every day. So a family can simply buy a (very small) LED light and a single rechargeable AA battery. They probably could find a shop to recharge the battery once every month, with minimal fee. Sounds much more reasonable than buying a 12.5kg pulley that needs to be reset every 20 minutes. * The fact that I've never heard of these amazing "single AA battery powered lights" sweeping through African homes makes me doubt your claim that it's "sufficient for reading and other activities". (Many Africans have cell phones; many more should be able to afford an AA battery.)

infodroid 10y ago
The problem is that the cheapest source of lighting for many poor communities is hazardous biomass fuels like kerosene. And unfortunately good alternatives like solar may not be a viable option for everybody. Sure there are many parts of Africa with good infrastructure, but just because you are living in Africa in the 21st century does not mean you are now surrounded by power lines! The nearest power socket might be a few dozen or even hundreds of miles away. How are you going to get there and back? If you don't succeed in charging your battery today because of floods or storms, will you go without lighting? And there is also cost and access to credit to account for. The GravityLight is targeting $5 price point, whereas a basic solar charging pack in Uganda costs approximately $150 USD on finance [1]. Compared to batteries, GravityLight has no operating costs. It also does not degrade over time, lose charge when it is unused, or unexpectedly stop working when the battery runs out. This might be an important consideration for some. As for whether the device can produce adequate lighting. A candle or simple kerosene wick lamp will produce around 8 lumens of light output [2] compared with the 16 lumens of the GravityLight. So this is pretty good. Each community has different needs and circumstances. Providing people with more alternatives to kerosene fuel will allow them to choose the solution that is right for them. [1] http://www.fenixintl.com/uganda/ http://www.fenixintl.com/uganda/ [2] http://evanmills.lbl.gov/pubs/pdf/offgrid-lighting.pdf http://evanmills.lbl.gov/pubs/pdf/offgrid-lighting.pdf