1. IP2.22.3 Introduction © Oxford University Press 2011 Introduction

2. IP2.22.3 Introduction © Oxford University Press 2011 Filament lamps and LEDs are both devices that transform electrical energy into light. The way they do it is very different and technological advancements have changed how they are used in everyday applications.

3. IP2.22.3 Introduction © Oxford University Press 2011  A filament lamp is a thin coil of wire which is usually made of a metal with a high melting point such as tungsten. When a current flows through the wire, it glows brightly and becomes hot.  The glowing filament gives off useful light but it also generates a lot of wasted heat.  These bulbs are very inefficient. Efficiency of a filament bulb is about 7.5%.

4. IP2.22.3 Introduction © Oxford University Press 2011  An LED, or Light Emitting Diode, uses special substances called semiconductors. When these semiconductors are arranged in a particular way they allow a current to pass through them in one direction but not in the other.  However, when the current flows light energy is emitted from the semiconductor. Very little heat is produced so this type of lighting is very efficient. Efficiency of an LED is about 75%.

5. IP2.22.3 Introduction © Oxford University Press 2011  Semiconductors only emit light of one frequency (i.e. one colour). For many years LEDs have been mainly red, green or blue.  However, with advances in techniques manufacturers now add phosphors inside blue LEDs which absorb and re-emit light of different colours. These LEDs create a mixture of light which looks nearly white.  This advancement and cheaper manufacturing costs has meant that they are now beginning to replace filament lamps with more efficient LEDs. LED lights use less energy, are smaller and also last longer.