By: Shravan S (RLBU)

In the midst of growing concern for air pollution, electrical power cuts, inflation, Delhi Government has banned the import and sale of Chinese crackers and banned the use of fire crackers from 10PM to 6AM this Diwali. Though the Government might be able to regulate the time frame in which the crackers are being fired, these bans are seldom useful in fostering the atmosphere from getting polluted. Here is how a simple technique of harnessing the natural light to lit up every dark room which is both economical and eco-friendly. Since solar power is abundantly available and we are talking about the natural light, you might be thinking of solar powered electric lights. You are partly right, the source of this light is solar energy but these are not electric lights, instead this bulb runs on water.

All we need is a transparent plastic bottle, water and little bleach. The principle used in this technique is diffraction of light. Diffraction is the bending of waves round an obstacle or through a hole.


As we can see in the above diagram, Diffraction is the bending of waves round an obstacle or through a hole.

The plastic bottle is filled with only water and bleach. The liquid inside the bottle harnesses the light from the sun, capturing and diffracting the light to all parts of the room. It is equivalent to a 55 watt light bulb. We need to make sure that the hole is not very big in size.

It consists of a 1.5l PET bottle filled with purified water and bleach (10 ml). Special glue is used to bond and seal the bottle to the roof. Adding the bleach to the water makes sure that the water stays clean and transparent without algae growing inside and turning the water green.


There are many places where this idea can be very effective. Consider a rural scenario where there is scarcity of electricity but abundance of natural light. More specifically, schools which operate only during the day. These light are a perfect solution for lighting up the dark rooms as they do not depend on electricity. Even in urban areas, many of the parking sheds can be equipped with these natural lights. This technique can be used in factories and go-downs which are single story structures.

Though the idea might look economical and eco-friendly, there are some major setbacks for this idea. It can only be employed in rooms which have roofs that can be exposed to sunlight. Moreover, the kind of roofs in which the bottles can be fixed are limited. This technique is restricted to availability of sunlight!!