Your questions answered: LED lighting specifications

Additional information from the July 28 Lighting: LED specifications webcast includes details about color shift, American Medical Association recommendations, and lighting controls. Presenters Haley Darst and Richard Vedvik tackle multiple questions.


Haley Darst, LC, Associate IALD, CannonDesign, Boston. Courtesy: CannonDesignBuilding owners are becoming more aware of and interested in selecting LEDs because of their energy efficiency and long lifespan. Good lighting enhances building design, conserves energy, and increases productivity, safety, security, and personal comfort. According to several government sources, up to 40% of the total energy used in commercial buildings is used for artificial lighting. The various codes and standards that dictate their design must be considered as LEDs are specified.

Engineers must understand the basics of LED lighting systems and which building types are best suited for them. It is important that engineers understand how to properly specify LED light sources when it comes to critical factors such as rated lifespan, lifecycle costs, efficacy, lumen output, compatibility with dimming controls, color rendering index (CRI), color temperature, and how LED lighting systems affect the electrical systems of the buildings in which they are installed.

Presenters Haley Darst, LC, Associate IALD, CannonDesign, Boston, and Richard Vedvik, PE, KJWW, Rock Island, Ill., take on audience questions from the July 28 Lighting: LED specifications webcast.

Question: To calculate footcandle (fc) by hand, the mathematical equation is 1 fc = 1 lumen/area (sq ft). How does the mounting height of the luminaire affect the result of this equation?

Haley Darst: You use the inverse square law for this:

E (illuminance; fc) = [ I (luminous intensity; cd) x cosine of incident angle of intensity] / d (distance: ft)2

This equation accounts for the effective surface area that actually catches the lumens arriving from a particular distance. The distance represents distance from the light source to the point in question.

Question: What specification provisions do you include regarding color shift when dimming LEDs?

Richard Vedvik, PE, KJWW, Rock Island, Ill. Courtesy: KJWW

Haley Darst: If you are NOT specifying a dim-to-warm LED product, I would first always check the MacAdam Ellipses information on the LEDs in question. ANSI recommends lamp manufacturers stay within a "four-step" ellipse (i.e. how far they can "stray" from the target before perceiving a difference in color on the CIE chromaticity diagram). The four-step represents a fairly large range of perceptible differences in color. One or two is noted as very good, and three is pretty common for manufacturers. Do your homework: Ask your lighting rep and get a working sample of both the product and dimmer in question so you can test it out yourself.

Question: At the onset of LEDs, there were a significant number of manufacturers that were not producing a quality product. Has this improved?

Haley Darst: Quality products have improved tremendously over the years. With that being said, there are inferior products out there, too. It's extremely important to try and get manufacturers in your office with real working samples of products so you can get a better understanding of their manufacturing techniques, warranty information, LED and driver information, dimming protocols, etc. Things are not always as they appear in pretty pictures—samples are a must nowadays. You will feel much better as a specifier if you can touch and feel the product and know that what you're specifying will leave the client happy.

Question: Did U.S. Green Building Council LEED adopt International Energy Conservation Code (IECC) 2012?

Richard Vedvik: LEED v4 has adopted ASHRAE Standard 90.1-2010.

Question: Provide the hyperlink to the American Medical Association study you mentioned.

Richard Vedvik: Find the information here.

Question: Have you seen the recent response from the Lighting Research Center to the American Medical Association (AMA) study?

Richard Vedvik: Yes, the link to the response is here.

Question: NEMA, IES, Lighting Research Center (LRC), and the Department of Energy have refuted the American Medical Association (AMA) claims. Please explain.

Richard Vedvik: The lighting industry feels that they should have been included in discussions before the AMA released a statement that used the term "harmful." The summary of the LRC response best explains why the lighting industry is not supporting all of the statements made by the AMA:

"Predictions of health consequences from light exposure depend upon an accurate characterization of the physical stimulus as well as the biological response to that stimulus. Without fully defining both the stimulus and the response, nothing meaningful can be stated about the health effects of any light source.

Notwithstanding certain sub­populations that deserve special attention, blue light hazard from In­Ga­N LEDs is probably not a concern to the majority of the population in most lighting applications due to human's natural photophobic response.

Both disability glare and discomfort glare are mostly determined by the amount and distribution of light entering the eye, not its spectral content.

In­Ga­N LED sources dominated by short wavelengths have greater potential for suppressing the hormone melatonin at night than sodium­based sources commonly used outdoors. However, the amount and the duration of exposure need to be specified before it can be stated that In­Ga­N LED sources affect melatonin suppression at night.

Until more is known about the effects of long­wavelength light exposure (amount, spectrum, duration) on circadian disruption, it is inappropriate to single out short­wavelength radiation from In­Ga­N LED sources as a causative factor in modern maladies.

Correlated color temperature (CCT) is not appropriate for characterizing the potential impacts of a light source on human health because the CCT metric is independent of nearly all of the important factors associated with light exposure, namely, its amount, duration, and timing."

Question: Do exterior lights emit high blue light that has negative physiological impact according to the recent American Medical Association warning?

Richard Vedvik: It is important to understand that the amount of "blue light" present depends on the color temperature of the lighting source. To my knowledge, there is not enough evidence to make statements stating exposure limits of certain wavelengths.

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