29-06-2016 | | By Martin Keenan
Now that LED technology is becoming widespread in all kinds of lighting applications, the focus is on making LED lighting products smaller and more energy efficient while maintaining long life and reducing cost. Manufacturers of passive and electromechanical components have come up with a few interesting developments that will help achieve these seemingly conflicting requirements.
Cooling is a huge issue in LED lighting because of the effect that excess heat has on the LEDs’ lifetime. Heatsinks are widely used, but sometimes it’s necessary to add active cooling to the design. The trouble is that traditional fans are bulky, noisy and unreliable. That’s the reason behind the development of fanless air mover products, which use an oscillating diaphragm to produce a jet of moving air. The diaphragm is frictionless making it reliable, robust and quiet. In an LED lighting fixture, these cooling jets can be used to create air flow over a heat sink so that a smaller one can be used. It’s actually possible to reduce the heat sink’s size by up to 60% using these devices. And because the air they expel is turbulent, they are very efficient (more heat can be removed with less air).
With higher and higher brightness COB LED modules being brought to the market, heat sink makers have had to find more inventive ways to remove more heat from smaller areas. Heat pipes are one way of doing this.
A heat pipe is a sealed, hollow tube with a fluid inside. At one end of the tube, the fluid evaporates and the vapour diffuses towards the other end, where it condenses and releases the heat it trapped when it evaporated. Cooled liquid is transported back down the tube using capillary action, with the resulting cycle able to transmit thermal energy hundreds of times faster than with solid heat sinks.
This technology is filtering down from aerospace applications to LED lighting. Mechatronix, for example, has developed a quadruple closed loop heat pipe structure it calls CoolTube (pictured), and inserted it into the centre of a COB module heat sink. This is an interesting idea because heat pipes can transmit energy vertically or horizontally, meaning the heat sinks can be used either way around, adding to design flexibility.
An important development in the world of COB holders is the recent publication of the Zhaga Standard’s Book 12. This new specification standardises six form factors for COB LED modules, allowing COB manufacturers to focus on areas where they can add value, such as efficacy and lifetime. Prior to publication of the standard, manufacturers’ choice of form factor for their COB modules was arbitrary, limiting lighting designers’ options for using products from different suppliers without changing the luminaire design.
Book 12 will of course have a knock-on effect for electromechanical COB holders. Later versions of Book 12 are expected to include standards for the holders specifying details such as the COB holder to luminaire interface definition. The result will be a rationalised landscape of holder sizes, allowing their makers to focus on value added differentiation such as thermal and interconnection properties of the holders rather than making hundreds of different sizes and types.
As part of the trend for intelligent lighting in smart buildings, LED lighting installations have become a lot more complex. With multiple lamps per system, central control and features such as dimming and changing the light colour, controlling these systems is starting to go beyond just one switch to switch them on and off. To serve this trend, connector manufacturers have developed a new breed of connector specifically for lighting, which combines power, data, control and communication functions. These hybrid connectors help keep luminaire housings as small as possible, because only one cable leading to one small connector is needed for all the connections to each unit.
Alongside current limiting and current sense resistors, inductors are frequently used to protect LEDs from over-current situations. Shielded inductors are typically used as non-shielded parts are not able to meet the required performance levels, but since the non-shielded parts are much cheaper, they are more attractive to high-volume applications. As a compromise, a new semi-shielded type has emerged which balances the performance of shielded inductors and the low cost of non-shielded types. These parts actually use a semi-magnetic shielding compound rather than the normal ferrite shield, which prevents uncontrolled magnetic coupling of the windings.
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