Types of lamps

 

Filament lamps (incandescent)

These have a metel filament which is heated by current flowing through it, the filament becomes hot enough to glow.

 

Discharge lamps

these contain a gas or vapour which emits light when an arc is struck

 

Led lamps

these have semiconductors that emit light when current passes through them. 

 

Selecting the best type of lamp for a given applicatin can depend on a number of factors

For example

Initial cost

efficacy

colour rendering. 

 

Filament Lamps 1

There are two main types of filament lamps

1.Tungsten

Tungsten halogen

Tungsten lamps

These need to be in a buld with the oxygen removes to prevent corrosion (oxidisation) of the filament.

However this means that atoms of tungston can evaporate off the filament into the vacuum and onto the inside of the buld, reducing the life of the lamp. 

 

Efficacy: Poor     Colour rendering:good.

 

Discharge lamps. 

In discharge lampsthe bulb or tube contains a gas or vapour, this normally has a very high resistance

This creates two problems

To strike the arc, a very high voltage is needed. 

Once the arc is struck, electrons are liberated form their atoms and the resistance becomes very low, We will need to limit the current to prevent burning out the lamp. 

 

Both these problems are solved by including control gear referred to as a ballast or choke and a starter, 

 

The mixture of gas or vapuor in the lamp affects the colour and other characteristics of the lamp

There are various types of dscharge lamp

 

Low pressure mercury

Are ordinary florescent lamps that are low pressure

Florescent lamps are types of various wattages come in standard lengths. COntrol gear is seperate from the tube.

Compact flourescents (cfl)

Control gear is internal

 

led lamps

Control gear is internal

 

As with all discharge lamps, the arc current passes through the gas/vapour causing the atoms to emit light. 

But low pressure mercury emits mostly in the ultraviolet range

This is both dangerous and not very useful. 

 

High pressure mercury

These lamps emit light in the visable and ultraviolet range, the uv problem is dealt with in two ways

Some ways are clear but have an outer bulb made from a special type of glass that absorbs uv light

These lamps emit slightly blue white light

Others have a phosphor coating that works in the same way as LP mercury, the re-emmitted light helps with colour rendering. 

Often used for high bay lighting. 

 

Low pressure sodium

These lamps have very good efficacy, but very prro colour rendering. They emit a yellow light with a touch of orange. 

They used to be street lights, but they have been replaced with LED. 

 

High pressure sociul

These lamps give a slightly orange light, but have a better colour rendering. 

 

Metal halide

These lamps have very good efficacy and rendering. 

They are new and replacing other types of lighting

High bay lights

Commercial and industrial lighting

Car parks

Sports arenas

Security lighting, 

 

Led

They use a semi conductor materials that emit light at the atomic level when a current flows through the,

They have a very long life

Many styles of led are avaliable. 

 

Safe disposal, as we have seen most lamp types contail materials that are hazardous or toxix, 

The waste electrical and electronic equipment regulations 2006 require that lamps and tubes are intact and disposed of by specialised contractors.

 

Summary

Incandescent (filament)

tungsten

Tungsten halogen

 

Discharge lamps

LP mercury (flourescent)

hp mercury

lp sodium 

hp sodium 

hatal halides

 

Led's

 

Safe disposal.