The inside of a fluorescent tube is coated with special materials. When the lamp is switched on a current of electricity flows through the vapour in the lamp. The current causes the vapour to make ultra violet light. This strikes the material coating the inside of the glass in the lamp and makes it glow. As soon as the current is switched off the vapour stops making ultra violet light and the fluorescent material stops glowing. The energy changes which take place in a fluorescent lamp are as follows: Some of the electrical energy in the current is changed to energy in the ultra violet rays. When the rays strike the fluorescent material some of their energy is changed into light energy which is released from the lamp.

You may have seen a watch that glows in the dark. This is coated in phosphorescent material but it works in a slightly similar way to fluorescent material. The phosphorescent material stores energy when ordinary light strikes it then when it is dark the phosphorescent material releases this energy as light.