Your questions answered: LED lighting specifications
Building 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?
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.
Question: For a new lighting design installation, how long in man-hours does it take a lighting controls contractor to program each light fixture to its addressable point into the lighting control software?
Richard Vedvik: For a recent project, it took the contractor less than a day to program an entire 10,000-sq-ft building.
Question: What about heat aspects of LED specifications? LEDs don’t radiate the heat so it gets trapped in the device.
Richard Vedvik: This is where the LM80 and TM21 test data and extrapolation are of interest because they include thermal performance. Fixtures with better heat dissipation and improved thermal management can perform better and last longer, which the test data should reveal.
Haley Darst: LEDs produce a significant amount of heat and it is essential to have proper thermal management. Many manufacturers use heat sinks on their products to move heat away from the junction. Optimizing the surface area and using materials that have a high thermal conductivity is necessary.
Question: LED manufacturers are claiming 100,000 hours for an average life of their lamps. Is there any research to confirm or refute that? How long can realistically be expected for and LED lamp?
Richard Vedvik: The projected lifetime can be calculated with the TM21 standard using LM80 test data
Question: Is there a life expectancy de-rating scheme for fixtures in poor environments—high heat or vibration—as is often the case in industrial settings?
Richard Vedvik: Yes, industrial applications can affect projected lifetimes. Refer to the manufacturer data for temperature de-rating. Cleaning of heat sinks may also be a good recommendation for the client to ensure proper heat dissipation.
Question: What are best control design tips for LED dimmable fixtures to match room lighting levels with daylighting opportunities?
Richard Vedvik: There are dimmable daylighting controllers that gradually adjust lighting levels. Thanks to addressable controls, multizone daylighting using multiple sensors is much easier than before. Daylight sensor placement is very important and the IES Handbook has good standards to reference.
Question: LEDs and associated fixtures have a long lifetime, in some case likely to outlive buildings or interior designs. Are used and refurbished fixtures acceptable in modern specifications?
Richard Vedvik: It is common to reuse fixtures due to aesthetics in public spaces, such as corridors. Remodel projects may benefit from fixture reuse.
Question: Do the LED comply with Federal Communications Commission (FCC) requirements for radio frequency interference (RFI)/electromagnetic interference (EMI)? What parts of the LED do and what parts do not?
Haley Darst: I would always check with the manufacturer of the product you’re questioning. Not just "any" LED product can go into a magnetic resonance imaging (MRI) suite. Manufacturers will list if a product is suitable for MRI rooms or if maybe a separate MRI filter is still needed. Always ask about the integrity and construction of the product—materiality of the housing, no gaps in construction (leaving circuitry vulnerable), and the driver design.
Question: What is the difference between 0 to 10 V and DALI?
Haley Darst: A 0 to 10 V dimming protocol essentially dims the product down to 10% of the original light output before it shuts completely off. 0 to 10 V dimming is typically the standard protocol for LED dimming on manufacturer’s cutsheets, also known as specification sheets. It’s low-voltage and has simple wiring. DALI is digitally addressable lighting, meaning each fixture can be individually controlled in a group. These fixtures can also give feedback to maintenance staff about energy savings, intensity, ballast info, etc.
Question: With regard to emergency lighting, I do not believe they should be dimmable.
Richard Vedvik: When dimming lights that are also used for emergency egress, controls need to be integrated which drive emergency egress luminaires to 100% output. Traditionally, this was achieved with a relay that bypassed the switch leg when we allowed luminaires to be turned off (such as conference spaces and performance spaces). Modern addressable controls allow for bypass as well.
Question: Can exit lights come with LEDs?
Richard Vedvik: Most exit signs available these days are LED. There are also LED bulb retrofit kits but I typically recommend replacing the entire sign since older signs may not meet modern requirements for visibility and letter size.
Question: Can the L-70 value be used to determine when the LED fixture will reach end of life?
Haley Darst: Yes, this value essentially means the "end of life" for the LED fixture. When you start adding in controls (daylight dimming, dimming, occupancy sensors, etc.), these mechanisms will start to increase the life of the system.
Question: Which standards for LEDs should be referenced by local government to develop an ordinance that limits sky glow, cumulative impact of light, and impacts to wildlife/human health (International Dark-Sky Association and other dark sky initiatives)?
Richard Vedvik: Dark sky compliance is the standard to reference and the IES Handbook covers this topic well. Note that even with full cutoff optics, reflectance off the pavement contributes to light pollution.
Haley Darst: Always ask about local ordinances and codes in the area. Some will have specific requirements for wildlife, too.
Question: In walk-in freezers and coolers, inspectors require 10 or 20 footcandles. Can it be provided by LEDs?
Richard Vedvik: Absolutely. Enclosed IP65 LED strips can easily achieve recommended lighting levels
Question: Have you heard about any issues with LEDs creating harmonic distortion?
Haley Darst: If looking to specify any light source, including LEDs in an area where harmonic distortion is a concern, it’s always best to look for information on the cutsheet and ask your lighting representative. Typically it’s the driver in particular that you would be concerned about.
Question: For dimming LEDs, what do customers want in terms of color correlated temperature (CCT)? Do they want the dimmed light to be shifted to a lower temperature, the same, or higher?
Richard Vedvik: Recent products have been available to shift color temperature lower (warmer) when dimming. I see the health care market embracing this in patient rooms and waiting areas
Haley Darst: This totally depends on the client. Some clients do want dim-to-warm—health care, restaurants, and high-end residential to name a few.
Question: What are the efficacy requirements for health care facilities? What are acceptable values?
Richard Vedvik: I don’t see requirements for efficacy; but instead, meeting necessary lighting levels while complying with energy code will naturally drive efficacy needs. I haven’t had problems meeting energy code and recommended lighting levels with efficacy above 100 lumens/watt.
Question: Are there any design programs available online? For example, I want 2 footcandles in a church parking lot. How do I design with LEDs?
Richard Vedvik: There are several programs available, some are sponsored by manufacturers and available at no cost. Each luminaire should have .ies files that include photometric performance. Note that there is a separate .ies file for each possible configuration. When considering outdoor lighting, pole height, optical distribution, and lumen output are all taken into consideration. The IES Handbook has an entire section on outdoor lighting recommendations for both level and uniformity. The design process using LED is the same as high-intensity discharge (HID), except designers now have more options.