LED LIGHTING Do LEDs measure up to the hype
WHO, WHAT, WHY WHO David Wren, managing director of Passmark Software Pty Ltd (Sydney) Background in Science from UNSW Specialising in performance measurements of SW & HW systems WHAT Started looking at LEDs as a hobby while building my own lights Now run a comparison web site and (somewhat ad hoc) LED measurement lab. WHY Absence of reliable unbiased technical information Make bucket loads of money (not, as it turns out). So continue to run it as a hobby.
LED HISTORY LED is a Light-Emitting Diode Low power LEDs have been around in electronics since 1962. Invention was in 1927 Early high brightness LEDs available since 1994 Rapid development over 3 decades More colours Higher brightness Are now on the brink of replacing all other forms of residential lighting but they aren t perfect.
MAIN TYPES OF (RESIDENTIAL) LEDS High voltage retrofit. 230V AC input GU10, B22, E27, E15 fittings In-built driver electronics Low voltage retrofit 12V AC input MR16 / GU5.3 fitting only Still contain some driver electronics. Use existing halogen transformer Kits Sold as external driver + LED No electronics in the LED itself Often a 3-pin plug on driver
LED DEFICIENCIES #1 - OVERHEATING Heat has two major effects Shorter life (esp. for built in drivers) Reduced output Consequence is that you can't get high wattage in small package Have been cases of 100% failure in enclosed fittings. Some LEDs throttle down when hot Source: Cree Xlamp Xm-l Datasheet Case temp ( C) Lumen Maintenance @ 6000 hours Time to L90 (permanent 10% drop in output) 45 98.0% 28,400 hours 55 97.2% 19,500 hours 85 94.5% 11,100 hours Source: Cree LM-80 testing results - Xlamp MX-6 White leds
LED DEFICIENCIES #2 CRI Colour rendering index (CRI) Measure of how close light is to natural light Ra is average of R1 to R8 CRI is not a great system, but is in common use Source: NIST CQS simulation 7.4 - Yoshi Ohno & Wendy Davis
LED DEFICIENCIES #2 POOR COLOUR EXAMPLES Typically ~CRI 80 Ra with a few at 90-95. Non uniform colour on cheapest LEDs. e.g. purple & yellow dots Poor binning, giving colour variation between batches CRI 95 LED Warm white Very close to an incandescent bulb CRI 72 LED Cool white Deficient in pinks and reds & excess blue
LED DEFICIENCIES #3 - FLICKER Various types of flicker & strobing High frequency flicker, but above fusion threshold, from driver / transformer. Low frequency flicker / strobing When dimming On ripple current at 10pm each night On lightly loaded transformers On incompatible dimmers & transformers Badly firing Clipsal 32E450LM Leading Edge dimmer causing strobing Yellow = input to dimmer. Green = output. Source: Gotolighting Brilliant brand GU5.3-MR16 100Hz flickering light output
LED DEFICIENCIES #4 MEDIOCRE DIMMING Don t dim to yellow / orange like halogens Sometimes flicker as they dim Don t allow full range dimming (0-100%). Is a lucky dip at the moment Other solutions (1-10V, DALI, etc.. are expensive and complex)
LED DEFICIENCIES #5 - EMI Some poorly designed LED lights cause radio interference to TV reception DAB Radio WiFi internet Garage door remotes Lots of other stuff Mirabella 5W MR16 LED purchased from Bunnings
LED DEFICIENCIES #6 VENDOR FRAUD (*) 20.3% of vendors claimed lower Watts than measured 14.4% of vendors claimed higher Watts than measured 5.4% of vendors claimed lower Lumens than measured 51.9% of vendors claimed higher Lumens than measured 50% of vendor have incorrect angle No way to verify safety claims in general No policing or audits by government Industry bodies are weak and have no teeth. (*) Based on measurements of 256 different LED globes. Only claims wrong by more than 10% are included. Includes cases where vendor had no specification or light failed before measurement was complete. In many cases it might be vendor ignorance & apathy, rather than fraud.
LED DEFICIENCIES #6 VENDOR TRICKS Vendor tricks used to inflate specifications Quote cold lumens (rather than at operational temp.) Sending golden samples for testing Quote cool white lumens (not the less efficient warm white LED colours) Vague meaningless language, Similar to 50W output Ignore power usage of drivers Ignore output losses from reflectors, diffusers & lens Comparing MR16 LEDs to extremely inefficient GU10 Halogens. Should compare MR16 LEDs to MR16 Halogens There is also a significant problem of fake components & mislabelling.
WHAT WE TEST Watts Power factor (PF) Lumens Angle & light distribution Flicker percent & index Spectrum, Colour & CRI Dimming Estimate running costs Efficiency (technically, efficacy) Running temperature All the above data gets turned into a web page on the site. http://www.ledbenchmark.com/
HOW WE TEST #1 WATTAGE AND PF Cheap power meters don t work at low wattages and poor PF levels Power-mate was a significantly more accurate Claimed accuracy is 0.2% with a voltage and current sample rate of 4800 / sec High PF (power factor) is desirable. Less power generation required So Less CO2, so greener. US Dept of Energy requires > 0.7
HOW WE TEST #2 LUMENS & ANGLE Home built Goniophotometer Freescale microcontroller & custom PCB Stepper motor PC with custom software Extech HD450 Lux meter Lumens is total light output in all directions. (not to be confused with Lux or Candelas) Angle is measured at 50% of max intensity
POLAR DIAGRAMS Polar diagram showing intensity of LED s output. Example shows a downlight with an angle of 101 (±50.5 from bottom) Maximum lux: 658 at 0 Total lumens: 420 Graph produced as output from the Goniophotometer.
TEMPERATURE MEASUREMENTS Low temperature = increased life. Use Testo 875 thermal camera Check if heatsink works & max temp. Generally the bigger the heatsink the better. Some first generation LEDs contained a tiny fan. Compact MortBay 6W MR16 LED Globe, case acts as heatsink Compact no name Ebay 3W MR16 LED Globe. No effective heat sink. Light failed after 1 h
SPECTRUM DATA & CRI UPRtek MK350 Spectrometer was used for colour measurements (CCT & CRI). Simple point and shoot device Also supplies CIE data graphically to determine how white the light appears
FLICKER DATA TAOS TSL257 high sensitivity light to voltage converter IC paired with a DPO2012b Oscilloscope. Can measure flicker up to ~10KHz Two measurements Percent flicker Flicker index Most flicker is invisible to most people (100hz) as it is above fusion threshold.
WHAT TO LOOK FOR IN A LED Kits are better than GU10 / MR16, but more expensive Drivers don t need to be so compact Electronics don t get cooked Heat sinks can be larger Wattage can be higher (and thus brighter) CRI 80 is minimum. Power factor > 0.9 if you want to be green Long warranty period Safety standards (SAA, C-Tick) Prefer vendors with a dimmer / transformer compatibility list. Test one or two units, before a large purchase Low running temperature (50C is excellent, > 90C is poor design) Efficiency of > 60lm / watt 5 times rule. To replace 50W of incandescent you need about 10W of LED. Don t spend too much, as there will be better cheaper gear next year Check that you have space in the ceiling or fixture (some LEDs are oversized) Low flicker (why have it if you don t need to) Unless you have a strong preference, use warm white (2700K 4000K)
FUTURE Intelligent LEDs Individual dimming Daylight sensing Occupancy & proximity sensing Smart phone controlled via wireless & APIs Marketing & Costs Running costs approach zero ($1 / globe / year) CFL & incandescent disappear Prices falling = Commodity item Long life = Less sales Only few large vendors survive More niche products Colour change / tuneable LEDs LEDs + cameras + speakers Better LED chips Brighter LED Less power usage Higher CRI 303 Lm / watt in the lab (March 2014, but only in lab conditions with low power) OLED Laser diodes Form factors Larger panels & ceiling panels Flexible panels Curtains, Carpets, Ribbons Slow death of the light socket Better driver electronics Better dimming Less flicker Better PF
HAITZ LAW Source: "Solid State Lighting", Phys. Status Solidi A 208(1), 17-29 (2011) "The story of a new light source", Nature Photonics, 1, 25 (2007). http://en.wikipedia.org/wiki/light-emitting_diode
QUESTIONS? Website: www.ledbenchmark.com Twitter: @PassMarkInc