Isang Litrong Liwanag - A Liter of Light Project - Do It Yourself

If one analyzes carefully, all that is happening is that sunlight comes in through a hole in the roof. All that the water does is to scatter the light in all directions because of the scattering molecules in the bleach. Even a spoon of milk will do the same thing. The amount of light is the same whether there is only the hole or the bottle fitted in it. If the beam comes in directly, it is like a spot and will not light up the place around. The water containing the bleach scatters the light to spread it in all directions.
If there was only a hole covered by a diffuser plate, it might work just as well. In the olden days of tiled houses one tile here and there used to be glass tiles, which had the same effect. These were appropriately called 'Sky lights'.

However, this is not to knock the effort of appropriate low cost technology in mitigating the problems of poor homes. I do appreciate and laud the social relevance of the effort.