The consortium defining interoperability for light engines has decided that LED engines with integral drivers must meet a new standard for dimmability.
The requirement that LED lamps be dimmable is one with which the industry has struggled. First of all, exactly what do we mean by dimmability in its broad outlines? How important is dimmability in the scheme of things? A quick poll in this community found that a large majority didn't consider it a universal requirement.
The inability of early compact fluorescents to respond as expected to legacy dimmers was one factor that turned much of public opinion against them. The LED industry, as we know, is determined not to repeat the mistakes pioneered by CFLs.
In the case of residential replacements for incandescent and CFL bulbs, most of the industry seems to have concluded that LED products have to work with at least a majority of legacy dimmers: some subset of leading-edge, trailing-edge, 0-10V, and Triac.
Now the Zhaga Consortium, which develops interface specifications that enable the interchange of LED light engines manufactured by different companies, has added a reference to an outside dimmability standard to its Books 2 and 8, which define socketable downlight modules with integrated drivers (which Zhaga refers to as "integrated control gear").
Since defining what dimming should mean falls far outside the consortium's mission, it worked with NEMA, the National Electrical Manufacturers Association, as that body collected input and worked toward a standard definition.
Such a standard emerged last April: NEMA SSL 7A-2013, "Phase-Cut Dimming for Solid-State Lighting: Basic Compatibility." (The standard itself costs $55 per copy; here is a free guide to its contents and scope.) It addresses how a driver should behave when a light engine is connected to a leading-edge dimmer.
The Zhaga initiative is not to everyone's liking. Some luminaire designers feel that a standard at the level of LED sources cramps creativity too much, as we mentioned in a nod to Lux Review's feature on "Heroes and Villains" of the LED lighting world. The magazine placed Zhaga in both categories.
What do you think? Does a dimmability requirement belong in a spec for the interchangeability of lighting components?
— Keith Dawson , Editor-in-Chief, All LED Lighting