2.4.6 Light through water

Figure 11: Types of DIY solar air heaters (Rimstar, 2005)

These designs shown in Figures 10 and 11 are all similar where cool air enters from the bottom, heats the air as it moves through the painted-black system (to absorb as much solar heat as possible), and then the hot air exits at the top to heat the room. The image to the left of Figure 11 is a screen design, where the air enters at the bottom of the system and moves in front of the black screen. The air exits at the top as it rises when heated by the sun-heated screen. In the ‘back pass with baffles’ system in Figure 11, the air enters at the bottom hole and is heated as it moves under a black screen in the direction of the exit hole as it is diverted. The last two images in Figure 11 indicate where the air enters the system and is heated as it moves through black painted cans (which are connected through holes at the bottom and top of the cans), or when moving through a black painted downspout.

2.4.6 Light through water

The law of refraction (or Snell’s Law) was discovered in the fifteenth century by a Dutch mathematician and geodesist Willebrord Snel van Royen. Figure 12 illustrates the refraction of a light ray as it hits the water.

Figure 12: Refraction of light in water (Science Learning Hub, 2012)

This effect is manipulated by filling a bottle with water and exposing it to sunlight. As the light enters the bottle of water, the light reflects back and forth as it travels through the water and lights up the room evenly (Figure 13).

Figure 13: Refraction of light in a water bottle (Bansod, 2015)

Figure 13 is a photograph of a bottle in the Liter of Light project.

Figure 14: Bleach-and-water filled bottle light (Mae 2018)

The Liter of Light project directs users to put a mixture of water and bleach into a plastic bottle. Sunlight is reflected from the outside, through the water and into the room. This bottle works most efficiently when installed in the roof. This bottle of light is a very inexpensive and adequate light source. Alfredo Moser had the original idea. He shared the idea with the nonprofit organisation MyShelter Foundation that started the Litre of Light project in 2012 in the Philippines. The goal of the project is to provide a sustainable alternative to electricity in poor areas. The life expectancy of a bottle is roughly five years. The one litre of water and three millilitres of bleach is cheap to replace.

Most countries carelessly dispose of plastic bottles. Roughly eight million tons of plastic end up in the ocean each year (Von Troscke 2015). This project reduces the amount of garbage discarded by re-using plastic bottles, and light is provided in poor communities. Thus, two problems are solved (Fielder 2017).