The T8 tube is a kind of fluorescent lamp (or fluorescent tube, light tube, fluorescent tube), and has a diameter of 1 inch and about 25 mm. It is a kind of gas discharge lamp. It uses electricity to activate mercury vapor in argon or helium to form a plasma and emit short-wave ultraviolet light that causes visible fluorescence to illuminate. A typical fluorescent tube is made of glass, and has sockets at both ends to connect the power source and fix the position of the fluorescent tube. In addition: T12 Diameter 38.1 mm T10 Diameter 31.8 mm T5 Diameter 16 mm T4 Diameter 12.7 mm T3.5 Diameter 11.1 mm T2 Diameter 6.4 mm Unlike a light bulb, the fluorescent tube must be provided with a ballast (also known as a "ballast") ), in conjunction with the starter, produces an instantaneous high voltage that ionizes the gas. Some new fluorescent lamps use different ionization methods than traditional fluorescent lamps. They do not need to use ballasts and starters, which saves energy and reduces the size, so that it can be used in the socket of traditional bulbs, also known as "energy-saving lamps" or "悭电胆".

working principle

The fluorescent tube is filled with a low-pressure argon or argon-helium mixed gas and mercury vapor, and on the inner surface of the glass fluorescent tube, a phosphorescent fluorescent paint is applied, and a filament coil made of tungsten is provided at both ends of the tube. . When the power is turned on, the current is first heated by the filament and the electrons are released. The electrons will turn the gas in the tube into a plasma, and the current in the tube will increase. When the voltage between the two sets of filaments exceeds a certain value, the tube begins to generate. Discharge, the mercury vapor emits ultraviolet light at 253.7nm and 185nm wavelength, and the phosphorescent fluorescent paint on the inner surface of the fluorescent tube absorbs ultraviolet rays and emits longer-wavelength visible light. The color of the emitted light is controlled by the proportion of the phosphorous component, while the glass tube prevents harmful ultraviolet rays and other harmful substances such as mercury from leaking out. There is a positive feedback relationship between the discharge current of the fluorescent tube and the on-resistance: when more current flows into the fluorescent tube, more gas is ionized, so that the on-resistance in the tube is continuously reduced, so that more current is generated. Into the fluorescent tube. If the fluorescent tube is directly connected to a fixed voltage power supply, the fluorescent tube will be burned quickly due to the rising current, so an auxiliary circuit is required to control the current entering the fluorescent tube at a fixed level, and this current control circuit is usually Known as the ballast. The ballast is actually an inductor. When the on-resistance drops to a very low level, the ballast's fixed inductive reactance and copper consumption cause the on-current to approximate a fixed value and start to work stably. Traditional ballasts need to be paired with a small component called Starter (commonly known as “Starta”) to make the differential between the filaments enough to discharge the fluorescent tube. The latest electronic ballasts do not. A starter is required because the start-up work has been included in the ballast.