Each new lighting technology brings with it a new set of questions and a new set of issues to address. These issues pertain to lighting metrics, as well as installation and application, all of which change the conversation and add another layer of terminology. While this has always been so, the introduction of solid-state lighting (SSL) and its widespread use has cajoled the lighting community into altering the industry's lighting jargon on a whole new scale, and I sometimes wonder if that hasn't steered the conversation about lighting off course, away from illumination.
With SSL technology, much more is at stake. The entire dynamic of the lighting system has changed, and lighting now seems to be less about individual components—the lamp, the ballast, the reflector, and the housing—that can easily be replaced when they reach a very clear end of life. Instead, SSL technology sets up a system where the components—the diode, the circuit board, the heat sink, and the driver—are integral to one another. When an LED reaches its end of usable life—or fails—you can't just switch out one diode.
I think that the lighting community has struggled with the conversion to LEDs because it has been confusing two different languages: the language of the chip (the diode) and the language of the LED luminaire. What a lighting designer needs to know about an LED fixture when making a specification choice is very different from what an OEM needs to know when designing a luminaire, or from what a chip manufacturer is concerned with when producing a diode. But all of this hasn't stopped the general conversation about LEDs from getting into a level of detail that similar conversations about previous light sources did not have to contend with. Does a lighting designer really need to spend his or her valuable time knowing how a luminaire's LEDs are binned? And to how many steps on a McAdam ellipse? Probably not, and yet we seem to be getting pushed into talking about this type of information regardless.
To get a handle on the discussion, many entities in the lighting community—including the IALD, the IES, the DOE, and individual manufacturers—have started to create “LED checklists” to help guide their various constituencies determine what questions they should be using to evaluate their LED choices.
As SSL technology continues to evolve, I do not doubt that these checklists will expand. At present, though, the core items a designer should be aware of include light output, color and color shift over time, thermal management, life and warranty, and testing.
The lighting industry has done a very good job, in a relatively short amount of time, of creating a new set of metrics that provide the framework for understanding how LEDs operate: LM-79, which deals with absolute photometry; LM-80, which addresses length of life; and TM-21, which looks at lumen degradation of the lumen package. These are a great help, but there is always the risk of designers, manufacturers, and sales reps referencing these guidelines, along with others, without really understanding what they are measuring.
And that brings us to the last, and perhaps most “invisible” part of the LED conversation—trust. Designers need to know that they can trust manufacturers to stand behind their products, and manufacturers need to know that they can source components from reliable vendors. You can ask for all the technical data you want, but if a company is not going to step forward and deal with problems that might arise, or if that company is not going to be in business six months from now, then it is irrelevant whether an LED is 100 lumens per watt or 160 lumens per watt. Rather than get caught up in the metrics of LED speak, let's not lose sight of lighting speak: trust and quality illumination.