> However, if it's inside a plastic case that blocks light, it doesn't.

You want an ordinary diode to allow current to flow easily when it senses light? Simple: shine a powerful laser at the plastic-encased diode and it will melt the plastic and liquify the metal, fusing it together and allowing current to flow again. See? You just needed to try harder.

Or if the hammer don't work, the sledgehammer is over there.