Thermal Energy Storage
GASEOUS DISCHARGE LAMPS: A gaseous discharge lamp is essentially a glass or quartz envelop containing two electrodes and a small quantity of gas or vapour at a low pressure. In these lamps light is obtained by applying an electric potential difference to a gas or vapour contained by the lamp under a suitable pressure. Due to application of electric potential difference gas gets ionised and an electric current flows; the tube is filled with a luminous discharge. The light spectrum obtained is however discontinuous (i.e. it consists of one or more coloured line). The colour of the light obtained depends upon the nature of the gas or vapour used.
Discharge lamps are of two types: 1) Those which give the light of the same colour as potential as produced by the discharge through the gas or vapour such as sodium vapour lamp, mercury vapour lamp, neon gas lamp. 2) Those which use the phenomenon of fluorescence and are known as fluorescent lamps. In these lamps, the discharge through the vapour produces ultraviolet waves which cause fluorescence in certain materials called the phosphorus. The inside of lamp is coated with phosphor which absorbs invisible ultra-violet rays and radiates visible rays. Example: Fluorescent mercury-vapour lamp.
High pressure mercury vapour lamp: It consists of a discharge envelope enclosed in an outer bulb of ordinary glass. The discharge envelope may be of hard glass or quartz. The space between the bulb is partially or completely evacuated to prevent heat loss by convection from the inner bulb. The outer bulb absorbs harmful ultra rays. The inner bulb contains argon and a certain quantity of mercury. In addition to two main electrodes a starting (auxiliary) electrode connected through a high resistance. The main electrodes are made of tungsten wire in shape of helices. In this case no separate heater is required for the cathode which is heated by the constant bombardment of the heavy mercury ions.
Discharge lamps are of two types: 1) Those which give the light of the same colour as potential as produced by the discharge through the gas or vapour such as sodium vapour lamp, mercury vapour lamp, neon gas lamp. 2) Those which use the phenomenon of fluorescence and are known as fluorescent lamps. In these lamps, the discharge through the vapour produces ultraviolet waves which cause fluorescence in certain materials called the phosphorus. The inside of lamp is coated with phosphor which absorbs invisible ultra-violet rays and radiates visible rays. Example: Fluorescent mercury-vapour lamp.
High pressure mercury vapour lamp: It consists of a discharge envelope enclosed in an outer bulb of ordinary glass. The discharge envelope may be of hard glass or quartz. The space between the bulb is partially or completely evacuated to prevent heat loss by convection from the inner bulb. The outer bulb absorbs harmful ultra rays. The inner bulb contains argon and a certain quantity of mercury. In addition to two main electrodes a starting (auxiliary) electrode connected through a high resistance. The main electrodes are made of tungsten wire in shape of helices. In this case no separate heater is required for the cathode which is heated by the constant bombardment of the heavy mercury ions.