LED Lighting Modules

LED Lighting Modules: Taking the Heat Out of the Situation
By James Stratford

The appeal of using LEDs in lighting applications is growing rapidly. The numerous and significant benefits of using modules that incorporate a matrix of LEDs are being recognized by design engineers in several key industry sectors, including aerospace, architectural lighting, and the “golden egg” automotive market.

Attributes such as design flexibility, low power consumption, even and reliable light, and long lifetime distinguish LED modules from designs based on traditional filament lamps and fluorescent tubes. LEDs can also have knock-on benefits, such as greatly reducing the size and complexity of the module and simplifying the lens design.

A good example of some other benefits of LED lighting is demonstrated by an application in the cabin of a passenger aircraft. A retrofit LED unit that replaced a fluorescent-tube lighting module enabled finely controlled dimming and also provided mood lighting through the use of differently coloured LEDs.

Thermal management

Perhaps the most challenging issue when realizing a module design that uses LEDs is to manage the temperature of individual device junctions during normal operation. If the considerable amount of heat produced by all the devices in a module is not managed correctly then the junction temperatures may reach a level where the LEDs’ expected life is shortened and reliability is compromised (see Links).

LED modules typically comprise a matrix of many surface mount devices. These LEDs are soldered to an etched copper layer that provides the interconnects between the individual LEDs as well as other passive and active components that are required to complete the circuit. The small size of the LEDs and the close proximity with which they can be mounted means that designers have a huge amount of design freedom and can achieve complex lighting patterns with high levels of brightness.

The etched copper circuit is separated from a base plate – usually made of aluminum – by a thermally efficient, electrically isolating dielectric material. The characteristics and capabilities of the dielectric layer are key to the design flexibility and performance of the overall module.