Dim to warm is the final piece of the LED puzzle (MAGAZINE)

+++++

This article was published in the Fall 2013 issue of Illumination in Focus.

Visit the Illumination in Focus archive page and view the e-zine version in your browser. You can download a PDF of the magazine from within the browser e-zine.

+++++

A short two to three years ago, LEDs were considered unfit for many lighting applications. The article contributed by Borden Lighting in this issue makes the point that the LED light source was formerly relegated to accent lighting. Today, LEDs can be used in virtually any application with greatly improved color quality and warm CCTs at high CRI levels. That was clearly the message that came through in The LED Show conference sessions back in August. If there is a weak spot in the capabilities of solid-state lighting (SSL) today, it's in the area of dimming, as one speaker at The LED Show highlighted.

Properly designed driver circuits can dim SSL products smoothly and linearly and also deliver linear energy savings. Problems arise when you try to dim LEDs with legacy phase-cut or triac dimmers. Those dimmers weren't conceived to work with a switching power supply such as the one in an LED driver, although electronics engineers are doing a pretty good job delivering drivers that can be powered by and interpret the intent of a legacy dimmer.

The other problem has been how LEDs dim. As the light level drops, LEDs generally maintain the same color temperature that they exhibit at full power. Incandescent and halogen lamps dim to a warm CCT at lower levels — a desirable aesthetic in the hospitality industry, particularly in high-end restaurants.

With many drivers for luminaires and integral LED reference lamps capable of supporting dimming, dim-to-warm capability is the final feature that should open the hospitality industry to LEDs. The functionality is generally achieved by adding some red or amber LEDs into a fixture or lamp. That addition requires a second driver channel to control the separate LED strings. And as the overall drive current is reduced, the percentage of energy supplied to the red channel is raised relative to that supplied to the white channel.

The result of dim-to-warm technology is lighting products that deliver 2700K–3000K CCT light at full power yet smoothly reduce the CCT to the 1800K range at the lowest light levels. The technology comes at a price with the dual-channel driver and additional LEDs. Still, the hospitality industry will gladly pay the price as that industry is still reliant on incandescent lamps and very high energy usage. Efficient compact fluorescent lamps (CFLs) or ceramic metal-halide sources have never been capable of that functionality.

Dim-to-warm capability came on the scene in a big way at Lightfair a couple of years back. I think Juno Lighting may have been the first to introduce the technology. Now most major luminaire makers have such a feature.

Now you can find the functionality in retrofit lamps. Osram Sylvania recently announced a broad line of 2500K lamps for hospitality applications and added to its family of Ultra SE lamps, with the SE implying Sunset Effect, or dim-to-warm functionality. Even luminaire makers that lack the engineering staff to design drivers that deliver dim-to-warm features can buy the technology in modular form. Cree just released LED modules that span 850–3000 lm with what it calls Sunset Dimming. LEDs are ready to crash the hospitality party.