<p>Inside the fluorescent tube is a gas mixture that is made conductive by a high electric voltage to the two opposite electrodes of the tube. This creates an electrical discharge. To "fire" the light you need a starter, which brings the electrodes to glow through the current flow. The glass bulb of the fluorescent tube is coated on the inside with a phosphor or halogen. This phosphor or halogen is excited by the resulting voltage during discharge and also begins to glow. Advantage of fluorescent tubes is the very high efficiency (60%) and the long life. The disadvantage is the large built due to its design and the lack of ability to concentrate the light.</p>