We all know that billions of us live in poverty, but I bet that most of us did not know that 1/5 of them spend almost 20% of their income on lighting alone. This is usually from kerosene lamps, which are a danger to health as well as being a major fire hazard in the slums, shanties and shacks of the poorest of the poor.
Step in the good ideas merchants.
The fist is the solar pop-bottle bulb capable of up to 60W of light, depending on conditions. All it is is a 2ltr clear pop bottle filled with cooled boiled water and a cupful of bleach then stuck through a hole in the roof and sealed in place - free lighting. Many shacks have few or no windows so this simple invention allows them to be used throughout the day.
But what about when the sun goes down...... step in Gravity Light. This British idea is little more than a modification of the Grandfather clock mechanism except that it is attached to a small generator and LED light. One lift of the pendulum = 30 minutes of light. The aim is to produce these for between £3 and £6 and for them to be user repairable with the minimum of tools and parts.
The only thing I would change with Gravity Light is to hand them out free. There will be approximately 500 million shacks around the globe. If each got two lights it would cost approximately £5 billion - a fraction of what the UK spends in aid each year - but it would save a fortune in kerosene and its related health and environmental costs.