108 TECHNOLOGY / LAMPS & GEAR
Rasib Khan, Engineering Manager at Harvard Engineering, analyses the effects of dimming on light quality and efficiency in a recent seminar from the LED Lighting Summit in Berlin.
DIMMED EFFICIENCIES
Top Graph showing the impact of dimming on the efficiency and power factor of Harvard’s LeafNut Enabled Twin LED Driver; Above Direct comparison of the efficacy of HID,CFL and LED Lighting systems when dimmed
With lighting consuming over 20% of the world’s electricity, according to the IEA, and the Carbon Trust saying it is responsible for approximately 23% of non-domestic carbons, ways to manage electricity consumption, including installing intelligent lighting drivers and control gear, are becoming more and more important. Technological evolution in LED light sources has further increased the scope of savings possible. Savings can be the most dramatic with LED lighting especially when the dimming capability of LED is utilised. Installation of intelligent and high quality drivers can result in great improvements in the power factor and efficacy of a lighting system. As a result, energy consumption can be significantly reduced. This is determined by LED system efficacy which in essence is influenced by three main factors;
control gear efficiency, LED efficacy and fitting optical design. It is naïve to take a driver’s efficiency on face value from the datasheet. For a true measurement of system efficacy the driver efficiency must be analysed when it is not running at full power, i.e. when it’s dimmed. With some of the largest energy savings coming from dimming LED lighting, control gear and drivers that remain highly efficient, with a high power factor when dimmed, can significantly improve system efficacy. LEDs are much easier to dim, with smoother adjustment and deeper dimming levels. In addition, LED efficacy improves greatly when the drive current is reduced, providing more lumens per watt. In essence, it gives greater value for money from an energy consumption point of view.
Recent independent tests that used Harvard Engineering’s LeafNut Twin LED driver, show that when dimmed, the system efficacy of LED lighting systems is greatly improved when compared to HID and CFL drivers. Harvard’s LED drivers can actually be dimmed to around 1%, with the system efficacy remaining high up to 20% dimmed levels. Below 20%, the system efficacy is impacted upon by driver efficiency (standing power). Independent testing also showed that Harvard’s drivers are the easiest and smoothest to control when compared to other products, with efficiency not dropping below 80% and power factor staying above 0.9. There is, however, further scope to improve control gear and power factor over the dimmed range, with many manufacturers still looking to overcome a number of challenges to achieve this. Improvements need to be made, for example, to drivers when they are dimmed to very low levels - less than 1% - to provide flicker free solutions. Installing high quality compatible products for specific lamps, that Harvard specialises in, is one way to resolve this potential problem. Driver efficiency across a wide output range could also be further improved. At present, the efficiency of Harvard’s drivers is 90% at full load and stays above 80% when dimmed down to 20% level. Intelligent controls, such as Harvard’s DALI control system, can also improve efficiency and make better use of existing dimming protocols. The company’s sophisticated and intelligent DALI solution can not only control installations small, medium and large, but individual luminaries as well. It has also improved interference tolerance. Constant investment is needed from specialist manufacturers, like Harvard, for high quality LED products and solutions to be regularly developed, at the same time overcoming current issues being encountered. Technical innovation and enhancements are the lifeblood of the industry, Harvard is at the forefront of many leading-edge technological advances, particularly in the LED lighting sector.
www.harvardeng.com
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