Container liquid level display e.g. for insect repellent

摘要

An insect repellent or air freshener is heated in a container using a heating device before dispersing around a room. To determine whether or not the container is still full, the container, which is optically transparent on one side (F), is illuminated with light from an LED. The colour of the light emitted by the LED is complementary to the colour of the insect repellent or other material (S) in the container. Since the insect repellent absorbs light, light only hits the inner wall of the container through reflection if the container is empty. The container may also contain water. The back wall (W) of the container is made of aluminium, which reflects light.