Latest Development on Drivers – Control and Dimming
While control is already used in many lighting applications, the share of controllable systems and the extend of control is expected to increase significantly in the coming years. One of the main motivations is the reduction in power usage that can be achieved, without affecting user value. The efficiency of LEDs has increased rapidly the last couple of years, but most of the prognoses imply that the efficiency will stabilize at around 200 lm/W. The next important area for energy efficient lighting will therefore be intelligent and user-oriented lighting controls. In an efficient lighting system (indoor as well as outdoor) that includes occupant detection and daylight harvesting, the energy savings can amount to 50% – 70%. Another reason is the increased focus on IoT, tunable white and human centric lighting, all requiring connectivity, control and extensive use of dimming.
Dimming of LEDs do however introduce some new challenges that has to be considered before specifying a new system.
One common pit fall is to assume a constant efficiency of the driver when dimming. In a simple use case control is added to dim the lights to 50% output in 50% of the time, this should give a saving of 25%. Most drivers do however drop around 5% in efficiency when dimmed to 50%, this reduces the energy savings by 6%. In many cases the drivers are further a bit over dimensioned for the luminaire, hence running at down to 50% when the luminaire is giving full output and 25% in the dimmed scenario. In this case the driver will typically drop 10% in efficiency in the dimmed scenario, this will cause the energy saving to be 12.5% less than expected. The above calculations are based on constant current dimming. If PWM dimming is used this will have an even greater impact, as the efficacy of the LEDs change with the current level.
Other elements that can severely affect the performance and user-experience when utilizing dimming are harmonic distortion on the grid, standby consumption, current ripple/flicker and dimming resolution/the step size at low intensity.
This lecture aims to describe these affects and how they can be avoided or handled. The material presented will cover many of the results from a nationally funded project (“Dimming, how?”) which will make a guide for designers of practical lighting systems on how to achieve optimal energy savings in LED-systems by dimming indoors as well as outdoors.