LED Surgical Task Lighting
Total Page：16
File Type：pdf, Size：1020Kb
BUILDING TECHNOLOGIES PROGRAM Technical Guidance Document: LED Surgical Task Lighting The U.S. Department of Energy’s (DOE) Hospital Energy Alliance (HEA) brings together leading hospitals and national associations in a strategic alliance designed to improve energy efficiency and reduce greenhouse gas emissions of healthcare systems throughout the country. By lever- aging access to advanced technologies emerging from the national laboratories, HEA members are creating a national forum for the industry to share evidence- based technology solutions and influence the energy performance of medical equip- ment and systems. In October 2010, acknowledging rapid LED surgical task light. Photo credit: Steris Corp. improvements in light-emitting diode (LED) technology, the HEA Lighting Project Team selected LED surgical task not require such filtering media, and their gical task lights. LED technology lighting as a project to explore in 2011. A higher efficacy can allow for reductions in may offer additional benefits, including scoping study was completed in January connected load of 50 percent or more, with enhanced mitigation of shadows cast 2011, characterizing the energy-savings potential for additional energy savings by surgical staff, as demonstrated in potential of currently available LED prod- through constant-color dimming and Figure 1.ii Some products even allow for ucts relative to tungsten-halogen (halo- reduced cooling load in the operating room. color adjustment. At present, however, gen) and high-intensity discharge (HID) Furthermore, while halogen lamps are typi- independent test data are generally not benchmarks.i This fact sheet was subse- cally rated for just 1,000 to 3,000 hours and readily available, performance in the later quently developed to provide objective fail catastrophically (sudden and without years of the product’s lifetime can only guidance to hospital owners and manag- warning), LED surgical task lights are be estimated, and products are relatively ers seeking to acquire high-performance generally rated for 25,000 to 40,000 hours expensive on a first-cost basis. Thorough LED surgical task lights. and are expected to “fail” by gradually product specification and evaluation are fading in brightness. Table 1 summarizes essential for a successful LED surgical Why Use LEDs for Surgical some of the primary benefits of LED sur- task lighting project. Task Lighting? LED technology is advancing into new cat- Table 1. Potential Advantages of LEDs egories of white light applications, including Parameter Benefit surgical task lighting, where early indica- tions suggest significant potential for energy Efficacy LEDs require less wattage to produce equivalent light levels. savings and reduced maintenance. The Heat in Beam Substantial thermal energy must be conducted away from LEDs, but halogen lamps typically used in surgical they radiate relatively little ultraviolet (UV) or infrared (IR) energy. task lights suffer from relatively low lumi- Dimmability Although system compatibility must be verified on a case-by-case basis, nous efficacy (lumens of light output per LEDs may offer dimming without color shift or flicker, thereby yielding watt of input power), which is only wors- additional energy savings. ened by filters that must be used to reduce the amount of non-visible radiation they Maintenance LEDs promise significantly greater life and a non-catastrophic failure mechanism. emit. LED surgical task lights typically do TECHNICAL GUIDANCE DOCUMENT: LED SURGICAL TASK LIGHTING 2 the second edition of the standard. Many to supplement CCT, thereby limiting such product datasheets have not been updated color variation.vii since the standard was revised, so com- parison between product ratings must be The NEMA/ANSLG standard simplifies performed with care to ensure manufac- specification of chromaticity, with allow- turers are consistently reporting depth of able measured Duv values ranging from illumination based on the current edition. -0.006 to 0.009 as a function of nominal CCT. Table 2 demonstrates that the NEMA/ Some IEC criteria provide fixed minimum ANSLG criteria are more stringent than the requirements or maximum restrictions, IEC criteria. The red text indicates five of 2 Figure 1. Shadow Dilution such as the 1000 W/m limit for total irra- the six IEC boundary points fall well out- diance. Other criteria provide ranges of side NEMA/ANSLG tolerances for white Photo credit: Cleveland Clinic acceptable values. For example, major light, suggesting the need for evaluation Industry Standard surgical luminaires (task lights or lamp- of Duv in addition to the IEC criteria for Performance Metrics heads) and surgical luminaire systems CCT and chromaticity coordinates. (having multiple lamp-heads) must pro- The U.S. Food and Drug Administration duce 40,000 to 160,000 lux of central illu- Similarly, the General Color Rendering (FDA), which grants marketing clearance minance. Because the value required by Index (CRI or Ra) may not provide an for medical devices, issued product testing surgical staff may fall anywhere within adequate measure of the ability of a light iii guidance in 1998 for surgical task lights. this wide range, specifications should source to enable color discrimination. This guidance encouraged adherence to the establish a set of narrower sub-ranges, CRI measures color fidelity of the test International Electrotechnical Commission where each sub-range is tailored to the source when lighting a set of pastel- (IEC) draft standard 60601-2-41, the second requirements of the associated surgical colored objects, relative to a reference iv edition of which was published in 2009. procedure. The number of lamp-heads source (incandescent or daylight depend- Many of the IEC criteria closely resem- should be determined in advance, since ing on CCT). Supplementing CRI, the ble criteria offered by the Illuminating together they must not exceed 160,000 lux. Special Color Rendering Index R9 evalu- Engineering Society of North America ates the ability of a source to render a (IESNA or IES) in Section 4.11 of its Color Characteristics saturated red object (having peak reflec- American National Standard, which have tance from 745 to 805nm), but it is not remained essentially unchanged since 1995.v The IEC criteria for correlated color tem- clear whether these two metrics together perature (CCT) and chromaticity coordi- provide an adequate measure of color The IEC criteria are currently used by FDA nates also require greater specificity. Two rendition in surgical lighting applications. Accredited Persons performing third- light sources of equivalent CCT are gen- party inspection of surgical task lights.vi erally expected to have equivalent color The Color Quality Scale (CQS) was devel- Considering existing protocol and the rel- appearance, with both being yellowish- oped by the National Institute of Standards atively high cost of testing products in this white, bluish-white, or something in and Technology (NIST) as an alternative category of medical equipment, it is rec- between. But if their chromaticity coordi- to CRI, after studies found CRI did not ommended that the IEC criteria continue to nates do not lie near the Planckian locus, correlate well with color preference for serve as the basis for product specifications. they can appear greenish or pinkish in color. some light source types, including LEDs.viii However, the IES recommendations merit The National Electrical Manufacturers CQS is largely modeled after CRI, with consideration, and surgical staff should be Association (NEMA), in cooperation with one major difference being the use of satu- surveyed to identify any refinements needed the American National Standard Lighting rated colors in lieu of pastels. Surgical staff to satisfy the requirements of various sur- Group (ANSLG), defined the Duv metric may wish to perform field investigations gical procedures. Additionally, in retrofit or upgrade applications, existing equipment 1 should be audited to provide an accurate Table 2. IEC Chromaticity Boundaries measure of baseline performance. Such an IEC point x coord. y coord. CCT (K) Duv audit could uncover any deterioration of A 0.310 0.375 6355 0.026 the UV-IR filters used for halogen products. B 0.310 0.307 6886 -0.007 The IEC standard provides definitions for a C 0.341 0.307 5006 -0.023 number of terms used herein. Note that D 0.420 0.370 3008 -0.012 “depth of illumination” was originally E 0.445 0.422 3010 0.006 defined by the IEC as the combined dis- tance upward and downward to points at F 0.380 0.422 4289 0.020 20 percent of the central illuminance, but this value was changed to 60 percent in 1Software allowing calculation of CCT and Duv from chromaticity coordinates is available upon request from Yoshi Ohno at NIST. TECHNICAL GUIDANCE DOCUMENT: LED SURGICAL TASK LIGHTING 3 to determine whether CQS offers any output should be established with an under- • Depth of illumination shall be no less advantages over the CRI and R9 metrics. standing of benchmark (halogen) lumen than [specify value] and no greater than maintenance. For example, if a given [specify value], or adjustable across Another potential concern is that some sur- LED light-head initially produces this range. gical task lights may produce color varia- 125,000 lux and its rated useful lifetime • Rated useful lifetime, defined as the tion across the surgical field. This would is based on the hours of operation to 80 not be evident from test data, and could hours of operation at greater than 80 percent of initial output (L80), then it would occur when an LED surgical task light percent of initial light output, shall be be a suitable replacement for a halogen no less than [specify value] hours. incorporating LEDs of more than one nom- light-head initially producing 105,000 lux. inal CCT is partially obstructed by surgi- • Dimming, if implemented, shall not cal staff. Ultimately, the color quality of a Specifying Products compromise the above criteria or cause surgical task light is best judged visually by excessive flicker, harmonic distortion, surgical staff, and in a mock-up scenario Requirements will vary between hospitals or electromagnetic interference.