The Light! The Light!
Due to be released on September 17th for the Game Boy Advance, Konami's Boktai is a fairly straightforward vampire hunter role-playing game. However, the cartridge has a solar cell in it which has a direct effect on gameplay. When sunlight strikes the cell, sunlight appears in the game. In fact, you can only defeat the bosses in the game by attacking them in daylight. Real daylight.
A number of gaming sites have tested the cartridge and its solar eye, trying to outwit the sensor and they've all come to same conclusion: this is the real deal. You want to be a vampire hunter? Check your six and keep to the daylight hours. The game takes you indoors on a number of ocassions and the presence of daylight on the sensor shows up onscreen as sunlight streaming through windows and other cracks in the architecture. Why is all this important? Well, other than keeping the ghoulies at bay, your weapons -- especially the Gun del Sol (naturally) -- recharge when they are exposed to the light.
Maybe it'll teach the next generation that solar power really is a viable source of energy. Paradigm shifts via video games.