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waveform only compound the incompatibility. LED ballasts provide the fundamental rectification and V-I conversion necessary to operate from AC voltage sources and, in dimmable devices, essentially map the duty cycle onto an output current range. In its recent Solid-State Lighting Spot Check, JAS Technical Media measured the illumination produced by various LED bulbs operating on a number of dimmers, using an incandescent bulb as reference. Data from one trial, typical of the spot check’s overall results, appear in figures 2 and 3. The plots normalize each bulb’s dimming curve to its own output with the dimmer bypassed. The graph’s horizontal axis is the power dissipation of a 100-W incandescent bulb reference, measured with the dimmer bypassed and at each test point along the dimmer’s travel. Better bulbs Sales of early generation LED light bulbs for residential service were sluggish for several reasons. Bulbs were available only in “daylight” (5000 K) colour temperature, which many see as unduly harsh for indoor residential lighting. Bulbs were only available with one or two options of lumen output. Pricing for early generation bulbs—typically $25 to $50—produced sufficient sticker shock to keep many homeowners on the sidelines. The market log jam broke a couple of years ago when Cree marketed 2700 K, 900 lumen bulbs for under $10 with street prices in the area of $8.50 in some home-improvement stores. Since then, LED bulbs have become available at reasonable cost in a wider range of lumen ratings and bulb shapes, making the technology more attractive to the full range of residential lighting applications. More recently, Osram Sylvania released a series of smart bulbs that integrate an 802.15.4 radio, processor, dimmable current drive, and the LEDs in standard A19 envelopes. These bulbs are compatible with Osram Sylvania’s gateway, allowing grouping, scene programming, and dimming without wall dimmers. Smart bulbs take a hefty premium at the cash register, but if you factor in the cost of a smart dimmer and the greater-than Figure 3: Compared to a reference incandescent bulb (left column), some companies’ LED bulbs exhibit indistinguishable dimmer waveforms (center column), whereas others alter the dimmer waveform (right column). Explanations for the differences were not available in time for this article. The oscillographs represent waveforms with the dimmer fully on (top row), at 75% power (ref incandescent power), 50%, 25%, and at the dimmer’s lowest setting (bottom row). (Figure courtesy JAS Technical Media; used by permission.) 11 year projected bulb life, they may be attractive, particularly for homeowners that do not want to get involved with installing new smart dimmers. Where home-automation might truly shine in residential lighting is in lighting arrangements not possible by other means. For example, in conjunction with automated controls, colour-tunable LED lamps can produce a range of effects. On the fanciful end of that spectrum, one can set the colour of, say, accent lighting in a living room to a deep blue to create an ambience reminiscent of a theatre for movie night or shift the light colour in a dining room toward red for a romantic dinner. More pragmatic, home-automation systems can program lights in a bedroom to fade up in time for waking with colour to match a sunrise culminating, if desired, with the high colour temperature of a cloudless sky. Although such systems remain untested in clinical settings, they may be particularly attractive to people in northern latitudes who suffer from seasonal affective disorder by simulating daylight—something incandescent bulbs cannot do. Ready, aim… … watch your feet. A good number of home automation systems have entered the market in the last year or so, but interoperability, or the lack thereof, may stunt residential-market adoption rates in the near term. Taking WiFi equipment as an example, you can buy a wireless router from Netgear, a rangeextender from Linksys, a printer from HP, and a camera from Canon and not care who makes WiFi silicon for any of those devices, not to mention your laptop, pad computer, or mobile phone. Interoperability is a given. If present at all, interoperability is far from obvious in the home automation market. Vendors’ marketing-collateral materials are essentially mum on the topic. So it appears that if you buy a gateway for one branded system, you are locked into that brand for all of your networked nodes and for your application software. Although technology aplenty is readily available, clouds on the horizon could be those of a coming market shakeout. The market is far from mature and there is plenty of opportunity and technical support for an upstart to jump in. For further information visit: www.mouser.com/applications Figure 2: Unlike those of just a few years ago, current LED bulb and dimmer designs produce smooth dimming with no flicker or audible noise at low levels. (Figure courtesy JAS Technical Media; used by permission.) www.electronics-eetimes.com Electronic Engineering Times Europe October 2015 9


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