Categories Lighting

Controlling Standby Power for Smart Lighting in Consumer Applications

Smart lighting is characterized by the sophistication in lighting control that has grown with the emergence of LED-based lighting. In fact, smart lighting is not practically achievable with traditional incandescent light sources and it is not as common with fluorescent light sources either.

To clarify: it is possible to control incandescent and, to a lesser extent, fluorescent light sources using phase-cut TRIAC dimmers and occupancy sensors. The driver circuits required for LED light sources, however, are more suitable to the low-voltage analog and PWM signals that are most readily associated with microprocessor control. But bringing the bulb within the control of a computer system opens up many other possibilities: power waste can be reduced; the user experience can be enhanced and the light source can even be used for data transfer. The challenge for smart lighting is to make use of all the functions afforded by computer control without losing efficiency – since efficiency was the reason the world looked to LED in the first place.

While commercial applications have already begun to adopt smart lighting, consumer applications are often tied to bulb-sized lighting nodes with low-power consumption, which makes the quiescent power consumption of the controller more of an issue. Consumers are unlikely to re-wire their houses simply to accept a hard-wired lighting system such as Power over Ethernet, Emerge etc., so most of the consumer-facing products in the marketplace today rely on wireless communication protocols (ZigBee, Z-Wave, Bluetooth or BLE, for example ) to control the lamp.

A 60 W A19 lamp today uses perhaps 7.2 W and is around 90 percent efficient – drawing approximately 8 W from the AC supply. ENERGY STAR suggests that the average bulb is on for less than three hours per day. The control electronics have to be on all the time, scanning for a start-up signal that will turn the bulb on. One popular smart-dimmable consumer bulb cites 0.45 W consumption in standby. If we ignore the power used by the base station (a base station can control 50 lamps), it means that the power consumption of the most common LED bulb is increased by around 50 percent by adding smart controls.

The ENERGY STAR Lamp Specification – Version 2.0 (Draft) has a section on standby power for connected lamps, with recommendations from various groups. 0.5 W has been proposed as a starting point. Several groups are pushing for a higher power level (>1 W was suggested during a recent presentation at Strategies in Light 2015).

This problem will get worse over time as LED conversion efficiency continues to increase (and therefore the power drawn by the lamp for lighting decreases).


Figure 1. DER-227(2) A 3 W power supply showing 70% conversion efficiency at 150 mW (0.3 A) output

How much power is required for a Wi-Fi transceiver?
The International Energy Agency (IEA) recently produced a report(1) which showed Wi-Fi transceiver standby/idle power use as being between 0.004 and 0.13 W. At this power level, power-supply conversion efficiency can be expected to achieve perhaps 70 percent (see Figure 1) suggesting a power budget of <200 mW would be achievable (and reduce control power to approximately 15 percent of the total power in the above example).

Smart technology for consumer LED bulbs and luminaires offers opportunities to fundamentally change how we use and experience light within the home. The benefits are significant but the fundamental benefit of energy saving must not be forgotten in the search for the limits of that new functionality.

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