ILLUMINATION

ILLUMINATION: 

The illumination is defined as the luminous flux received per unit area.

Mathematical illumination = Luminous flux / area = lumens/m2

INCADESCENT LAMP: 

The lamps consist of an evacuated glass bulb or gas filled having fine metallic wire within it. The filament material normally used is tungsten. Titanium and Carbon also used for filament. The filament should have the following properties.

1.       Melting point should be high

2.       Vapor pressure and temp coefficient should be low

3.       Material should be ductile and mechanically strong enough to  bear vibration during use

Tungsten filament lamps have an average life of100 hour under normal conditions.

SODIUM VAPOUR LAMP:  

This type of lamp is of low luminosity, so the length of this lamp is large. To get the required length it is made in the form of a ‘U’ tube.  Two oxide coated electrodes are sealed into the ends. The tube contains a little sodium and neon gas. The U tube is enclosed in a double walled vacuum flask to keep the temperature within working range. Before the lamp starts working sodium is in the form of a solid deposited on the side of tube walls. In the beginning it operates as a low pressure neon lamp with pink colour. The lamp gets warm, sodium is vaporized and it radiates yellow light and after about 10-15 minutes, the lamp starts giving full light.