Illumination Sources

Our everyday experience does not alert us to the need to choose lamps for Machine Vision carefully.  The human eye-brain complex is able to compensate for slow variations in both the colour and intensity of ambient lighting, without our ever becoming aware that any change has taken place. As a result, people often remark with surprise how bright the room suddenly appears when a light bulb has been changed. Unlike people, machines are very sensitive to variations in both colour and brightness. Incandescent filament bulbs and fluorescent tubes are used in the home and office, while mercury and sodium discharge lamps are commonly employed in street lighting and in factories and warehouses. For many years, advertising has relied heavily on “neon” displays. In addition, there is a new variety of lamps available, including a wide range of LED-based lighting units, cold cathode tubes, compact fluorescent bulbs and plasma panels. Arc lamps have been used in specialised scientific and industrial applications. For Machine Vision, the following properties of lamps are important:

The features of the major types of lamp are discussed. LEDs are almost ideal for many industrial applications and in recent years, there have been major advances in the design of LED arrays for Machine Vision. It is possible to build arrays in a variety of shapes. An array may contain LEDs of many different and precisely known colours. LEDs are efficient and stable over a long period. The lighting pattern can be adjusted dynamically, under software control.