The Basics of LED Lighting

Transcription

1 LEDs versus Conventional Sources: What are the differences? AATCC Conference 2017, Cleveland Ohio Naomi Miller, FIES, FIALD, LC Pacific Northwest National Laboratory Portland OR 1 The Basics of LED Lighting Very long life (25,000 hours up to 250,000 hours, defined by light output decay of chip) Most white LEDs are blue-pump or violet-pump chips, plus phosphor that converts blue energy to yellow and other colors Some LEDs are RGB or RGBA or RGBW, with 3 to 5 clustered narrow-band emitters VERY low failure rate in chips. Driver failure rate about the same as electronic ballasts. Requires a driver for current and voltage control, unless it s an AC LED Can be dimmed, but not always straightforward Luminaire energy efficiency ( efficacy ) around lumens-per-watt (lm/w) in white. 2 1

2 The LED Lingo The LED Die ( chip ) The LED Package or Device The LED Module or Array The LED Light Engine Source: Lumileds 3 The LED Lingo The LED luminaire Finelite.com Landscapeforms.com Lightingservicesinc.com hew.com 4 2

3 LED Efficiency is the sum of the parts + LED package/module efficacy + Thermal solution Gelighting.com Courtesy: Journee Resultant Full luminaire Luminaire efficiency efficacy Fixture/optical design efficiency + Power supply (Driver) efficiency 5 What s different? Lamp/ballast vs. Luminaire Efficacy X = 32 lm/w system efficacy Lamp and ballast efficacy = 64 lm/w 1800 lumens Fixture efficiency = 50% 900 lumens delivered You can t compare CFL lamp lm/w to LED luminaire lm/w = 86 lm/w system efficacy LED system efficacy = 86 lm/w 1025 lumens 6 6 3

4 Calculations What s different? Relative photometry (for luminaires with conventional sources, based on selected lamp and ballast) Absolute photometry (for LEDs, based on specific luminaire selected Photometric reports for LED luminaires are called IES LM-79 reports Sphere data is color information, lumen output, and efficacy (lm/w) Gonio data is candlepower distribution data, for directional light intensity. This also yields lumen output and efficacy (lm/w) 7 7 LED Life What s different? Conventional lamp life is point in time where 50% of sample lamps have burned out. (MH, HPS, FL, INC, HAL, etc.) LED life is defined as when the initial light output of sample LEDs has decayed to 70%. Called L70 life. LED decay rate depends on ambient operating temperature and thermal design of luminaire. IES LM-80 test runs provide data on expected light decay under specific conditions. A luminaire manufacturer uses that data to predict life at L70 or L90, for example. L70 life may overestimate longevity due to continuous burn testing 8 8 4

5 Light Loss Factors What s different? Conventional lighting: LLF = LLD X LDD X BF X RSDD Where LED lighting: LLF = Light Loss Factor LLD = Lamp Lumen Depreciation LDD = Luminaire Dirt Depreciation BF = Ballast Factor RSDD = Room Surface Dirt Depreciation LLF = LLD x LDD X RSDD Where LLF = Light Loss Factor LLD = Luminaire Lumen Depreciation LDD = Luminaire Dirt Depreciation RSDD = Room Surface Dirt Depreciation 9 9 Light Loss Factors What s different? What does the IES say about LLD values? Use L70 (that is, LLD = 0.70) That means you are overlighting by 40% when new. Consider using LLF of 0.85 instead Specify LEDs with replaceable LED modules Providing dimming to the system Document your assumptions and reasoning Document your calculations There is no IES-sanctioned alternative yet. Reputable luminaire manufacturers may provide L70 life information on their spec sheets to help you. If it says L70 is 150,000 hours then you can be more confident it will maintain its lumens a long time

6 Interchangeability of components What s different? You re outa luck!! There are few standards for LED modules LED linear modules Drivers Client must get replacements from original manufacturer Interchangeability of components What s different? How about T-LEDs? Some are interchangeable But it s TRICKY Many different wiring options Some have remote drivers Tubes that operate on fluorescent ballasts are probably interchangeable Try them out before buying a bunch of them

7 Specifying color What is different? LED color spectrum is not standardized Spectral Power Distributions (SPDs) vary widely Color rendering properties vary widely 3000 K LED, Phosphor Violet Pump Specifying color What is different? CCT is still as useless as ever 2700K 3000K 4000K 5000K

8 Specifying color What is different? CRI is still a poor metric. Color Rendering Index (CRI or R a ) was developed as a fidelity metric Developed in the 60s to describe color rendering of fluorescent lamps Metric based on 8 pastel colors Does not include saturated colors, does not evenly represent all areas of color space It s the average of the relative ability of a light source to render those 8 colors, compared to a reference source at same CCT Ranges from 100 to below 0 in scale (LPS has CRI of -44) CRI can over or under-estimate color rendering ability compared to human perception Some lamp manufacturers have learned to game the system R9 value used in addition to CRI to give better estimate of color rendering ability in red hues, but values are skewed because of distorted color space New IES TM-30 color metrics are much better for all sources Developed by IES Task Force of color scientists, manufacturers, and designers. R = Rendering f = fidelity g = gamut Based on 99 object colors more evenly distributed in color space Fidelity and gamut are still compared to a reference source (Blackbody or daylight or a mix of the two) Color fidelity of a single color sample ranges between 0 and 100. Specific information about chroma shift in specific hue bins can help you predict preference. 16 8

9 Is color fidelity always the goal? No. Sometimes a little boost in color saturation draws your eye, makes that apple look more appetizing, makes your skin look healthier. This is described through color gamut. A boost in color saturation necessarily reduces CRI values. Photo: GE Lighting Reference Source Test Source 17 Examples of chroma shift in red Desaturated (e.g. R cs,h1-10%) Normal saturation (e.g. R cs,h1 = 0%) Read, chroma shift of hue angle bin 1 = 0% Highly saturated (e.g. R cs,h1 +10%) 18 9

10 How to use TM metrics in your practice Look at tables of CRI, R f, R g values for familiar light sources to develop your own scales of acceptability for different applications Use R f just as you used to use R a where 80 = good; 90 = excellent (except R f is more reliable) Use R g to look for wonky color sources Use R cs, h1 chroma shift values to look for red rendering (-1% to 15% preferred) Source Type Description CCT CRI(R a ) R f R g R cs, h1 Tungsten Filament MR16 Halogen 12V % Tungsten Filament A-lamp 75W Halogen % Tungsten Filament A-lamp Neodymium Incand % LED Phosphor Blue Pump LED module 3000 K % LED Phosphor Blue Pump MR K 12V % LED Phosphor Blue Pump MR K 12V % LED Phosphor Violet Pump MR K 12V % LED Phosphor Violet Pump MR K 12V LED Hybrid Phosphor blue pump + Red LED % Fluorescent Broadband F32T8/ % Fluorescent Broadband F40T12/C K % Fluorescent Broadband F34T12/ES Lite White % Fluorescent Broadband F34T12/ES Cool White % Fluorescent Broadband F40T12 Cool White Deluxe % Fluorescent Broadband F34T12/ES Warm White % Fluorescent Narrowband F32T8/ % Fluorescent Narrowband F32T8/ % Fluorescent Narrowband F32T8/ % Fluorescent Narrowband F32T8/ % HID (Mercury Vapor) 100W Deluxe phosphor % HID (Quartz Metal halide) Standard MH 100W 4K Clear % HID (Ceramic Metal Halide) 100W MH 4K Protected % HID (High Pressure Sodium) Standard HPS % HID (High Pressure Sodium) White HPS % Daylight model CIE D % Daylight model CIE D % Equal energy model Flat SPD - no spectral differences % 19 Dimming What s different? Be careful using incandescent dimmers with LEDs Apparent load. Repetitive peak currents from LED/driver system may affect apparent load to the driver, so you may overload a 600W dimmer with a mere 150W LED load! Minimum load. Dimmed LEDs may not draw enough power for the dimmer to recognize it. No persistence. LEDs exhibit no luminous persistence, so flicker can be a problem. Switch ~75% dimmer ~25% dimmer Check LED compatibility with dimmer, or goofy things can happen

11 LED lamps Dimming compatibility report For a specific LED/driver product: Tells you which makes/models of dimmers work Min # of lamps or luminaires on dimming circuit Max # of lamps on dimming circuit What low end of dimmed output is (%) Whether flicker or other instability is noted 21 Dimming What s different? LED Dimming Drivers and their dimming techniques: PWM (pulse-width modulation) CCR (constant current reduction) Hybrid of the two Drivers are paired with a dimmer that sends a signal such as: Phase cut (forward or reverse) 0 10V DALI DMX Wireless signal (Zigbee, Bluetooth, etc.) 22 11

12 Maintaining dimming compatibility Move away from phase-cut and 0-10V dimming protocols to DALI, DMX, or wireless signal Substitutions of dimmer, luminaires, lamps, transformers can affect compatibility.. Avoid mixing light sources on single dimming circuit (different LED drivers, mixed halogen and LED, mixed LV and 120V.) Effect of time on specifications: Project delays LED/driver generation changes Dimmer evolution Luminaires discontinued or changed design Do mockups. Be careful with substitutions of lighting or dimming products on your projects. You may lose compatibility 23 Flicker 24 12

13 Flicker Terminology Repetitive change in magnitude over time, or modulation, of the luminous flux of a light source Light source modulation (all light sources flicker to some degree) Visible, invisible, perceptible, detectable (sensation) Sensation: External conditions are detected; neurons respond Visible flicker = Luminous modulation is sensed and perceived Invisible flicker = Luminous modulation is sensed, but not consciously perceived Flicker factors for both Visible and Invisible Flicker Modulation Frequency Modulation Amplitude Average output (also known as DC Component ) Duty Cycle 25 Flicker Flicker plots from magnetic ballast fluorescent and electronic ballast fluorescent No flicker (smooth fan of light from rod) Flicker (stripes of bright and dark in fan) 26 13

14 Flicker Implications Problems include Headaches and migraines Malaise Photosensitive epilepsy Short exposure to 3 70 Hz flicker (i.e., visible modulation) may cause seizures in sensitive people Also static repetitive geometric patterns 1 in 4000 people Onset around puberty; 75% remain sensitive for life Autistic children are more sensitive to flicker. It may increase agitation and autistic behaviors. (Rates of autism are approximately 1 in 68, per the CDC.) Industrial accidents due to stroboscopic effects Reductions in reading speeds and comprehension Distraction 27 LED products more likely to flicker Many AC LED products Some vintage-look filament decorative LED lamps LEDs with simple/inexpensive drivers LEDs dimmed with some Phase-Cut dimmers LEDs dimmed with some Pulse Width Modulation (PWM) drivers 28 14

15 Application - Where Flicker Matters General lighting Hospitals/clinics Classrooms Task lighting Industrial spaces Offices Application - Where Flicker Matters TV studios/videoconferencing Videoconference facilities (Anywhere video cameras are used)

16 Where flicker is less important Roadways/parking lots/pathways Non-professional sports and industrial lighting on 3-phase electrical system Very low intensity holiday lighting? Flicker Avoidance Recommendations Flicker Limit Proposal from IEEE P1789 Committee: Hand-held flicker meters are now available. Test to determine the flicker frequency of the SSL product (It should always be > 100Hz) Test to determine the % Flicker of the SSL product over the full dimming range Multiply the frequency by 0.08 to get the Allowable %Flicker If % Flicker of the SSL product is LOWER than the Allowable Flicker, then the product is acceptable for all but the most unusually sensitive individuals. If frequency is difficult to determine, % Flicker shall not exceed 10%. Specifiers: If flicker test data is not available, do mockup with actual products (especially drivers) and actual dimmers, over full dimming range. Use finger wave method to check for flicker

17 How LEDs are changing the design of lighting Stuff LEDs can do that conventional technologies can t do easily or efficiently: Smaller form factors of luminaires Color change (SPD, CCT) Visual pizzazz Retail seasons Alertness or relaxation Matching daylight Circadian rhythm support LED Downlights that dim to warm Dimming of streetlights, outdoor lighting, industrial fixtures, in response to occupancy or time of night Much better color than available from metal halide or HPS lamps Improved optics for almost everything USAI Lighting Stanford University campus, Ken Rice Photography 33 Thanks for your lively attention! Thanks for your kind attention! Naomi Miller, FIES, FIALD, LC Naomi.Miller@pnnl.gov Pacific Northwest National Laboratory Portland OR 34 17