The Lucky Bamboo is put in a kind of flower pot. A moisture sensor is inside the flower pot. The moisture sensor works with the resistance difference between water and air. THe resistance of water is much lower than air. If the resistance is decreasing we know there must be water.

The sensor is then connected to a UV lamp. The lamp is
controlled via the sensor and lights up according to the sensor data.

A dragon is painted on a wall. We use transparent UV Color. So there is no dragon if there is no water inside the flower pot, but if there is water the dragon will be illuminated by the UV lamp. It lights up blue.