White LED Luminaires

in Buyer's Guide

For a PDF of the April 2009 PLSN Buyers Guide, CLICK HERE.

In this, our annual “green” issue of PLSN, we are focusing on that technology which has made not only the single biggest impact on the industry in the last 10 years, but also which has the most promise for the next 10 years and beyond. That technology, of course, is LED luminaires. To gain better insight about the current state of the art and the future of the technology, we consulted two experts in the field from Osram Opto, Marc Dyble and Brian Terao. 

PLSN: The problems we have faced using LEDs in the live event production industry have been several fold, including the lack of smooth dimming, low CRI, high cost, and low brightness. There has been much improvement in these areas; can you put these issues in perspective with regard to how far we’ve come and how far we have to go?

Marc Dyble: Upon introduction to the entertainment lighting industry, LEDs were primarily considered for use in novelty decorative and accent applications since they did not perform as well as the incumbent light source. Years of continual research and development on the chip, package and system levels have resulted in increased brightness and efficiencies, allowing LEDs to make their way into high-bright applications.  However, there is a cost differential between the traditional light sources and LED-based fixtures. Incandescent and halogen tend to have low upfront costs and high operating and maintenance costs over the life of the fixture. In contrast, LED-based fixtures have a higher upfront cost, with payback coming from the lower operating and maintenance costs of the fixture. At the discrete level, premium performance is associated with a higher cost; however, as the dollar per lumen ($/lm) costs continue to decrease, payback periods will shorten and enable higher adoption rates.

The ability to duplicate the slow fade and warm glow of an incandescent lamp is the defacto standard when it comes to lighting. With regards to color rendering (CRI), phosphor is preferred over mixed monochromatic due to its broad spectral emission. With new phosphor mixtures at the chip level, high CRI, on par with halogen sources, is available today. Hybrid fixtures utilizing both phosphor and monochromatic sources provide color temperature and CRI tunability, allowing for increased flexibility in lighting design. Recent advancements in LED drivers have enabled flicker-free, continuous dimming schemes to mimic analog controllers with greater dimming range capabilities. In addition, plug and play drivers are now available to interface directly into existing dimmer architecture without additional wiring.

At one point, all of these advancements would never have been thought possible, but today, solid state lighting is in the limelight.

There are a number of different claims as far as the efficiency of LEDs in lumens per watt. What is the real story? Does Haitz law still hold? If so, for how much longer will it be true?

Brian Terao: For white LEDs in the Sun White to Daylight White range (as defined by ANSI 5000K-6500K) performance of 100lm/W+ are reported. For "warm" temperatures, these can be 75lm/W or higher.  However, one needs to clarify the specific color temperature and CRI.  The warmer the CCT and higher the CRI, the less efficient the devices is, generally speaking. In addition, lm/W for an LED component is only a reference point at a given drive condition under specified test parameters.  For example, 100lm/W @ 350mA for 25ms.  In an LED system, one can see 30 to 40 percent in efficacy losses due to thermal, optical, and electrical impacts.  What is the real story?  The real story is that LEDs continue to penetrate more and more applications due to efficiency improvements and sound system design that minimize efficacy losses.

As LED components have demonstrated levels of $/lm that enable solid state solutions, the parameters of have changed to focus on overall lm/W in both a component and system, and quality of light. Haitz Law only looks at price/output of a component, and solid state lighting is much more beyond that.*