Life on earth is made possible by energy from the sun, which arrives mainly in the form of visible light. About 30 per cent of sunlight is scattered back into space by the outer atmosphere, but the rest reaches the earth's surface, which reflects it in the form of a calmer, more slow-moving type of energy called infrared radiation. (This is the sort of heat thrown off by an electric grill before the bars begin to grow red.) Infrared radiation is carried slowly aloft by air currents, and its eventual escape into space is delayed by greenhouse gases such as water vapour, carbon dioxide, ozone, and methane.

Greenhouse gases make up only about 1 per cent of the atmosphere, but they act like a blanket around the earth, or like the glass roof of a greenhouse -- they trap heat and keep the planet some 30 degrees C warmer than it would be otherwise.

* Human activities are making the blanket "thicker" -- the natural levels of these gases are being supplemented by emissions of carbon dioxide from the burning of coal, oil, and natural gas; by additional methane and nitrous oxide produced by farming activities and changes in land use; and by several long-lived industrial gases that do not occur naturally.

* These changes are happening at unprecedented speed. If emissions continue to grow at current rates, it is almost certain that atmospheric levels of carbon dioxide will double from pre-industrial levels during the 21st century. It is possible they will triple.

* The result, known as the "enhanced greenhouse effect," is a warming of the earth's surface and lower atmosphere. The IPCC assesses with very high confidence that the globally averaged net effect of human activities since 1750 has been one of warming. The ‘best case’ computer climate models estimate that the average global temperature will rise by 1.8° C to 4.0° C by the year 2100. A temperature increase of 0.74° C occurred last century and for the next two decades, a warming of about 0.2° C per decade is projected should greenhouse gas emissions continue to rise at their current pace and are allowed to double from their pre-industrial level.

* A rise in temperature will be accompanied by changes in climate -- in such things as cloud cover, precipitation, wind patterns, and the duration of seasons. In its Fourth Assessment Report, the IPCC projects that heat waves and heavy precipitation events are very likely to increase in frequency in the 21st century. In a world that is crowded and under stress, millions of people depend on weather patterns, such as monsoon rains, to continue as they have in the past. Changes, at a minimum, will be difficult and disruptive.

* Carbon dioxide is responsible for over 60 per cent of the "enhanced greenhouse effect." Humans are burning coal, oil, and natural gas at a rate that is much, much faster than the speed at which these fossil fuels were created. This is releasing the carbon stored in the fuels into the atmosphere and upsetting the carbon cycle, the millennia-old, precisely balanced system by which carbon is exchanged between the air, the oceans, and land vegetation. Currently, atmospheric levels of carbon dioxide are rising by over 10 per cent every 20 years.

Lighting is one major area of electricity consumption and it is estimated that about 19% of global electricity is consumed for lighting. This comprises of both indoor and outdoor lighting. Manually controlling the lighting circuits is laborious and is prone to errors and unaffordable costs calling for reliable automation systems to save on cost and energy. Dynamically dimming the HID lamps offers an opportunity to conserve more intensely during late night or off peak hours.

The lighting automation offers a substantial scope for conservation and there by contributing to reduction of Green house Gases. Many of the efforts are being recognized under Clean Development Mechanism called CDM leading to grant of Carbon Credits either as CER's or VER's eligible for carbon trading.

Our information says that a variety of models were tried out in India but the users are unanimous in concluding that these are not reliable. The problems spelt out are

1. The device behaves erratically due to dust accumulation on the sensor window.
2. The device failure due to rain.
3. The device behaving erratically due to clouds and rain leading to switch on of lamps even during the day.
4. The device failure due to over voltages in the mains.
5. The device failure due to short circuit in the load line.
6. The device failure due to thermal factors.