A Study on the Solar Illumination Provided by a Water Bottle

Abstract

This paper provides experimental evidence to show that the “Litre of Light” (LOL) bottle is a better option than a glass plate covering the hole in the ceiling for providing sufficient illumination during daytime in congested settlements with insufficient illumination (slums). To model the room, a 70cm x 70 cm x 70 cm wooden box was constructed, and a 2liter coke bottle filled with drinking water was fixed to the roof of the box with 1/3rd of the bottle outside the box. The illuminance profile of the box floor was measured using a light sensor for different positions of the Sun in the sky from sunrise to sunset (by covering the roof hole first with LOL bottle, and then with glass plate). It was found that less than 0.7% of incident illuminance reaches the box floor after passing through the LOL bottle and less than 1.2% after passing through the glass plate. The LOL bottle was found to provide sufficient illumination for reading over a larger area of the room for a longer part of the day than a glass plate, in spite of the fact that the loss in illuminance when direct sunlight passes through a glass plate or a LOL bottle is very high. The peak intensity region was found to lie on diametrically opposite corners of the floor as compared to that found with a glass plate. This indicates the possibility of total internal reflection happening inside the LOL bottle.