Physical cryptography provides cryptographic protocols using physical objects like cards and envelopes instead of using computers. In this paper, we introduce a new model for physical cryptography, called light cryptography. It uses transparent sheets and some properties of light and shadows. We design several secure light cryptographic protocols: one for set-intersection (which can solve the scheduling problem), one for maximum (which can solve the Yao's Millionaires' problem), one for computing the sum of integers. We believe that our protocols using light cryptography are a powerful tool for information security education because they are fairly simple and fun to use.