Solar Bottle Lamps: Water + Bleach = 10,000 Liters of Light
Here's a cheap way to bring light into a dark shed during the day while cutting down on your electricity costs. Fill a plastic bottle with water and two cap-fulls of bleach and stick it through the roof. The bottle refracts the sunlight into the space and generates as many lumens as a 50 watt bulb. It's free light!
The bleach in the bottle keeps nasty stuff growing inside. Add a black film canister to the top to keep the plastic cap from melting. Properly installed, one of these should last you several years.
The "solar bottle lamps" or "solar bottle bulbs" were developed in Brazil where they quickly became popular in the slums. There, some dwellers can't afford to add windows to their houses or there may not be space as each house is up against each other. Also, the corrugated steel roofs, even if the folks could afford it, can't support the weight of skylights.
Of course these lights only work during the day so you'll need a backup light system. But for spaces where you normally have to flip on a light even when it's high noon, this DIY hack is one bright idea.