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Luminaires based on Secondary Phosphors

Dr Jim Methven , Dr Philip Pickering, Mr Ahmad Makkaoui School of Mechanical Aerospace and Civil Engineering Dr Huw Owen School of Materials. Luminaires based on Secondary Phosphors. Acknowledgements.

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Luminaires based on Secondary Phosphors

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  1. Dr Jim Methven, Dr Philip Pickering, Mr Ahmad Makkaoui School of Mechanical Aerospace and Civil Engineering Dr Huw Owen School of Materials Luminaires based on Secondary Phosphors

  2. Acknowledgements • The authors express thanks to the Joule Centre in The University of Manchester for financial support in the early stages of this work and to the Higher Education Innovation Fund (HEIF) for a recent award • We also express thanks to the following for the provision of materials and facilities : Andrew Murray of the Photon Science Institute in The University of Manchester; David Nauth of Intematix; Paul Ripley of Phosphor Technology UK; Caroline Prior and Paul Eustace of Lucite, JuhaRoyhkio and Simon Aldred of Ledil, Cheryl Owen and Mark Slonker of Perrite, Nicola Horan of Future Lighting , Peter Thorns of Thorn Lighting and Morton Graham of Innovations in Light. • The authors also wish to acknowledge the Excel work-up of the CIE plots used here which was described originally by Donald Schelle, of Texas Instruments (http://www.edn.com/design/led/4375668/Accurately-Plot-Colors-from-Power-Spectrum-Data) LuxLive, November 20, 2013

  3. Scope The LED group in School of Mechanical Aerospace and Civil Engineering (MACE) in The University of Manchester has been involved with high brightness LEDs for more than 5 years Over the past two years the group has focused on the manufacture of remote phosphor optical elements by injection moulding The presentation provides an overview of both the manufacture and characterisation of remote phosphors and focuses on measurements of light transmission, chromaticity and excitation Designs for luminaires which incorporate remote phosphors are also considered LuxLive, November 20, 2013

  4. Background (You know this!) The vast majority of white LEDs owe their existence to the invention of a commercially viable process for manufacture of blue HBLEDs by ShujiNakamura in the mid-1990s from strongly p-type GaN Blue LEDs can be down-converted to longer wavelengths by using commercially available phosphors By using one or more phosphors in separate layers, LED manufacturers can produce a range of white lamps which range in colour temperature from 2500K (warm) to over 6000K (cool) and hence target different markets The more common phosphors include Cerium Doped Yellow Garnets [YAG:Ce3] and Red Nitrides LuxLive, November 20, 2013

  5. Phosphor Action lmax500-600nm lmax430-470nm Cool White Blue Source Yellow Phosphor lmax> 600nm Warm White Red Phosphor LuxLive, November 20, 2013

  6. Conformal Phosphor Arrangement (Schematic) Silicone or Epoxy Lens Silicone Encapsulant Typically < 3mm Conformal Phosphors Junction Solder Connection (2) Slug Pad for External Heat Sink LuxLive, November 20, 2013

  7. Remote Phosphors • Phosphors which are not applied directly to the LED junction have become known as remote phosphors lmax> 600nm Yellow Phosphor Red Phosphor Blue Source White Light lmax430-470nm lmax500-600nm SP Distance? PP Distance? Losses? Quality? Cost? Material (Efficiency)? Composition? Host? Material (Efficiency)? Composition? Host? LuxLive, November 20, 2013

  8. Manufacture of Remote Phosphor Elements • Casting • Poor Reproducibility, Non uniform dispersion, Separation • Injection Moulding • Inexpensive, many host materials are available, aluminium tooling is relatively cheap A simple diffusion plate 85mm by 85mm by 2mm was used as the vehicle for the remote phosphor The mould was made in Aluminium. Aluminium Mould LuxLive, November 20, 2013

  9. Preparation of Phosphor Mouldings • Each composition was made by tumble blending the phosphor with the host polymer and then injection moulding the composition on an Easimould T7/30 injection moulding machine • The plates weigh roughly 18g and hence a 1% loading is equivalent to 18/100 = 0.18g = 180mg • Taking the cost of a phosphor as £5/g, this is equivalent to an additional 90p per plate with the bonus of beneficial diffusion 3% YAG:Ce in PS 1% LWR in PS LuxLive, November 20, 2013

  10. Vacuum/Plug/Free Forming • Vacuum forming typically requires a sheet precursor • Vacuum formed mouldings have non-uniform thickness • Nonetheless it is possible to vacuum form a simple shape such as a hemisphere from an injection moulded plate LuxLive, November 20, 2013

  11. Range 2% Gal 535 2% Gal 550 1% LWR 6831 NYAG 4355 + LWR GAL 535 + LWR 1% YAG:Ce 2% YAG:Ce 2.5% YAG:Ce 3% YAG:Ce 2% NYAG 4355 LuxLive, November 20, 2013

  12. Illumination: Light Box (SPE) • The light box is a closed light mixing chamber that acts as a simple Scattered Photon Extraction (SPE) device • The internal walls of the chamber are lined with a microcellular reflective sheet (MCPET) • The source is clamped in a fixed location at one end of the box • The phosphor-containing plates are secured by means of a spring-loaded sliding clamp at a location with the box and in front of the source LuxLive, November 20, 2013

  13. Experimental Set-Up for SPD Measurements Light Box Variable Constant Current Source LED Source Plate YAG:Ce Phosphor Plate Spectrascan PR-655 Complete Rig LuxLive, November 20, 2013

  14. Does it get warm? • Simple equilibrium heat balance using a 1W source term in an acrylic plate the same size as that used for the phosphor • Nominal 8W/m2K film coefficient on all exposed surfaces • Maximum temperature rise of 9oC • So the answer is yes and no LuxLive, November 20, 2013

  15. Source LED: Philips Lumileds Radiance, W/sr/m2 (Radiometric) The curves are SPDs of the outputs from the two different source LEDs though a 3% YAG:Ce plate Royal Blue: LXML-PR01-0500 Blue: LXML-PB01-0023 Wavelength, nm LuxLive, November 20, 2013

  16. Spectral Power Distributions (Spectrascan PR-655) Conversion to photometric data requires manipulation with standard CIE calibration curves By introducing the red phosphor the SPD is stretched into the red end of the spectrum (>750nm) LuxLive, November 20, 2013 Blue

  17. Typical SPD Trend YAG:Ce + LWR 2% YAG:Ce 2.5% YAG:Ce 3% YAG:Ce We’ll come back to this! LuxLive, November 20, 2013

  18. Emission Measurements: Fluorolog3-22 (Horiba) • This device is a tuneable monochromator which is powered by a Xenon 450W lamp • It allows the excitation wavelength to be set at a fixed value and records the resulting response SPD via a a cooled R928P photomultiplier tube which operates in photon-counting mode LuxLive, November 20, 2013

  19. Binning: Luxeon Blue and Rebel ES LUXEON Rebel Colour Portfolio Datasheet DS68 20130718 LuxLive, November 20, 2013

  20. Response to Monochromatic Excitation 3% YAG:Ce Excitation Wavelength, nm Within experimental error the peak for ALL excitation frequencies is 530nm LuxLive, November 20, 2013 Blue

  21. R Routine - This is just for interest! chromxy<-function(CF,SPD) { ProdX<-SPD$Count*CF$XX[CF$WL %in% SPD$WL] ProdY<-SPD$Count*CF$YY[CF$WL %in% SPD$WL] ProdZ<-SPD$Count*CF$ZZ[CF$WL %in% SPD$WL] sums<-sum(ProdX,ProdY,ProdZ) x<-sum(ProdX)/sums y<-sum(ProdY)/sums return (c(x,y)) }  > coords<-chromxy(CIE1931ML,YP3) > coords [1] 0.3776349 0.3390774 The Calibration (Observer) functions are contained in a text file with five columns: XX, YY, ZZ, Count and WL(Wavelength). The SPD has two columns: Count and WL The X, Y, Z tristimulus values are obtained by piece-wise integration of the spectral power distribution (SPD) with the observer functions CF$XX, CF$YY and CF$ZZ over the range 380 nm to 780 nm The chromaticity coordinates are given by LuxLive, November 20, 2013

  22. Illuminance Measurements: Goniophotometer • Illuminance measurements were taken with a Glen Spectra PR-525 • All measurements were made along the lamp azimuth and at a distance of 1m • The LED was run from a bespoke constant current source at 1.45W and was allowed to run for 10 minutes before any measurements were taken Glen Spectra 625 Backboard Slot Inclinometer Lock Nut Arm Slot Rotating Arm Pivot Phosphor Plate LED LuxLive, November 20, 2013

  23. CIE Plots - ALL Data • The cluster at the bottom left with chromaticity co-ordinates x<=0.2 and y<=0.2 comprises single red phosphors and some GAL phosphors • The majority of the points lie on two approximately straight lines which emanate from the chromaticity co-ordinates of the source • The yellow and yellow/green phosphors lie on the steeper of the two lines while combinations of yellow/green and red phosphors lie on the shallower line • The shallower the slope the warmer is the white output 520 540 560 580 2.5 3 4 600 6 2 1.5 620 10 490 700 480 470 LuxLive, November 20, 2013

  24. CIE - YAG:Ce Loading in Polystyrene • The extremum of the YAG:Ce has chromaticity co-ordinates x=0.41 and y=0.58 • The addition of the long wavelength red (LWR) plate rotates the extremum to x=0.49 and y=0.51 • The locus of the YAG:Ce + LWR line crosses the Planckianlocus above 3000K YAG:Ce 0.5%-4% 520 YAG:Ce 0.5%-4% + LWR@1% 540 560 580 2.5 3 4 600 6 2 1.5 620 10 490 700 480 470 LuxLive, November 20, 2013

  25. CIE: YAG:Ce Loading in PMMA (Acrylic) • The extremum of the YAG:Ce has chromaticity co-ordinates x=0.41 and y=0.58 • The addition of the long wavelength red (LWR) plate rotates the extremum to x=0.5 and y=0.5 • The locus of the YAG:Ce + LWR line crosses the Planckian locus just below 3000K • Both phosphors appear more effective in PMMA compared with PS YAG:Ce 1%-3% 520 YAG:Ce 1%-3+ LWR@1% 540 560 580 3 2.5 4 600 5 2 6 1.5 620 10 490 700 480 470

  26. YAG: Stacked Plates (PMMA) • The YAG:Ce stack is slightly convex with extremum chromaticity co-ordinates at x =0.42 and y=0.58 • The addition of the long wavelength red (LWR) plate rotates the extremum to x=0.5 and y=0.51 • The locus of the YAG:Ce + LWR line crosses the Planckian locus above 3000K 1% YAG:Ce x1-x3 520 2% YAG:Ce x1-x3 540 1% YAG:Ce x1-x3 +1% LWR 560 2% YAG:Ce x1-x3 + 1% LWR 580 3 2.5 4 600 2 6 1.5 620 10 490 700 480 470 LuxLive, November 20, 2013

  27. Other Phosphor Stacks 2% NYAG x1-x3 • The GAL 535 response is not linear and with the LWR crosses the Planckian locus above 6000K • The NYAG and GAL 550 points lie roughly on the same line with the extremum at x=0.4 y=0.6. The addition of the LWR plate rotates the extremum to x=0.48 y= 0.52 • The locus of the YAG:Ce + LWR line crosses the Planckian locus well above 3000K 2% NYAG x1-x3 + 1% LWR 2% GAL 535 x1-x3 560 2% GAL 535 x1-x3 + + 1% LWR 2%GAL 550 x1-x3 580 3 2.5 2%GAL 550 x1-x3 +1% LWR 4 600 5 6 2 1.5 620 10 490 700 480 470 LuxLive, November 20, 2013

  28. More Red … 520 3% YAG:Ce 540 3% YAG:Ce + 1x 1% LWR 3%YAG:Ce + 2x +1% LWR 560 • The extremum of the YAG:Ce has chromaticity co-ordinates x=0.41 and y=0.58 • The addition of the long wavelength red (LWR) plate rotates the extremum to x=0.49 and y=0.51 • The addition of an additional red (LWR) plate rotates the extremum to x=0.545 and y=0.455. This crosses the Planckian locus well below 3000K at roughly 2200K 580 2.5 600 6 2 1.5 3 620 4 10 490 700 480 470 LuxLive, November 20, 2013

  29. Red Phosphor Interpolation Data from Previous Slide Target area requires roughly 1.6 “plates” of LWR LuxLive, November 20, 2013

  30. Add a Red Source 520 540 • Points reflect the step-wise (100mA) increase in current (L-R) from a red LED located alongside the blue source • The phosphor plate contains 3% YAG:Ce 560 580 3 2.5 4 600 2 6 1.5 620 10 490 700 480 lsource=627nm 470 LuxLive, November 20, 2013

  31. SPD for Phosphors with a Red Source Current through additional red source at 627nm 0mA 100mA 300mA 400mA LuxLive, November 20, 2013

  32. L-Prize: Philips 423244 - $50.00 LuxLive, November 20, 2013

  33. Typical SPD Trend YAG:Ce + LWR 2% YAG:Ce 2.5% YAG:Ce 3% YAG:Ce We’ll come back to this! LuxLive, November 20, 2013

  34. … or is it? Remember all the SPDs are for stacks of a YAG: Ce plate (at various loadings) and a 1% LWR plate Note the shape of the 1% Yag: Ce 1% YAG:Ce LuxLive, November 20, 2013

  35. Phosphor Emission Profiles for 1%LWR • The graphs show the emission profiles of the 1% LWR when excited with 445 nm (blue) and 530 nm (yellow) wavelengths • The relative areas under the peaks at 445nm and 530nm is about 2.5. • Hence at low levels of yellow phosphor there is enough of the blue source to excite the LWR phosphor directly • At higher levels of yellow phosphor the overall red conversion is reduced since the predominant wavelength for excitation is now around 530nm LuxLive, November 20, 2013

  36. Light Output • Around half the light output is lost in the transformation of the blue source to a CCT around 3000K • Another half is lost in the transformation from 3300K to 2200K YAG:Ce in PS CCT =5236 YAG:Ce in PMMA CCT =4671 YAG:Ce in PS + 1% LWR YAG:Ce in PMMA + 1% LWR CCT =3377 YAG:Ce in PS + 2x 1% LWR CCT =3046 CCT =2200 LuxLive, November 20, 2013

  37. YAG:Ce (3%) in XPS LuxLive, November 20, 2013

  38. Conclusions • This work has shown clearly that secondary optics which incorporate phosphors (garnets and nitrides) can be manufactured by injection moulding • These optical elements are effective as remote phosphors in the design of luminaires and may be simply stacked together in the correct sequence to produce white light output in the CCT range between 8000K and 2200K • While the results are in broad agreement with other sources, it is difficult to establish a direct comparison since the loading of the phosphor and the method of application is not clear in these reports • Nonetheless, by way of comparison, a 3% loading by weight represents a surface loading of roughly 6mg.cm-2 • Binning control by remote phosphor is restricted to intensity (thickness) rather than frequency LuxLive, November 20, 2013

  39. Remote Phosphor Design Configurations B A C A: Simple B: Separated C: Separated Secondary Optic D: Capped E: Capped Secondary Optic Variable Geometry D E LuxLive, November 20, 2013

  40. Questions? LuxLive, November 20, 2013

  41. Binning Issues: Uniformity? LuxLive, November 20, 2013

  42. NYAG 2% Acrylic LuxLive, November 20, 2013

  43. LWR Acrylic LuxLive, November 20, 2013

  44. Control? • The Fluorolog measurements embrace the bin extremes • The Fluorolog measurements show ALL the excitation frequencies are down-converted to around 530nm • It follows that binning control by remote phosphor is restricted to intensity rather than frequency • Intensity can be controlled by the phosphor thickness LuxLive, November 20, 2013

  45. CIE 1931 Chromaticities Optic #5 (3% YAG:Ce) Optic #11 (3% YAG:Ce + 1% LWR6931) The chromaticity co-ordinates of both systems are shown on a 1931 CIE diagram along with the Planckianlocus. Optic #11 (x=0.377, y=0.339) is just off the locus while optic #5 (x=0.283 y=0.289) lies on the locus Both are within the range of white light as represented on a CIE 1931 diagram and in effect optic #5 produces a cool white light while optic #11 produces a warm white light. LuxLive, November 20, 2013 Blue

  46. Illuminance and CCT LuxLive, November 20, 2013

  47. Raw Measurements (Goniophotometer) Outside the range of the instrument • The YAG:Ce phosphor is effective at loadings between 3% and 4% (optics #5 to #7) • At 3% loading (optic #5), produces a realistic efficacy (lumen output per unit power) and a cool white light • When the red phosphors are introduced optics (optics #8 to #11), there is a measurable shift to longer wavelengths, making the light warmer although at the cost of a reduced output Source Illumination: Philips Luxeon Rebel LXML-PR01-0500 LuxLive, November 20, 2013

  48. Design Opportunities • It is relatively straightforward to create a multi-layer moulding with each layer containing a different phosphor providing the relatively high tooling cost is acceptable (A) • Only the moulding farthest from the source LED has to be the shape of the required optic (C,E) • The source LED can be “capped” by a hemispherical (or other geometry) moulding which contains the phosphor with the highest excitation energy (lowest wavelength) and a second phosphor with a lower excitation energy (higher wavelength) can be moulded into the shape of the target optic. The size of the cap need only be a few millimetres larger than the source LED and its only requirement is that it does not affect the output luminosity distribution (D,E) LuxLive, November 20, 2013

  49. Findings • Figure 4 shows the spectral power distribution curves of optic #5 and optic #11 from Table 1. Note that the ordinate in Figure 4 is a radiometric measure of the light output rather than a photometric measure. Conversion to photometric data requires manipulation with standard CIE calibration curves [15]. Optic #5 produces an intense blue peak from the source LED and phosphorescence to around 650nm. By introducing the red phosphor in optic #11 the large blue peak from the source LED is reduced and the SPD is stretched towards the red end of the spectrum (>700nm). LuxLive, November 20, 2013

  50. Findings • From Table 1 it would appear that as the loading of the YAG:Ce phosphor increases so too does the light transmitted through the plate (#1-#7). Obviously this would contradict Beer’s law. In fact as the loading of the phosphor increases so too does the amount of blue light converted by Stokes’ effect to longer wavelengths. Since the light meter cannot detect short wavelengths, the measurable output increases as the longer wavelengths are created by the phosphorescence effect. Note that the YAG:Ce phosphor is effective at loadings between 3% and 4% (optics #5 to #7). At 3% loading (optic #5), the YAG:Ce phosphor produces a realistic efficacy (lumen output per unit power) and a cool white light. When the red phosphors are introduced optics (optics #8 to #11), there is a measurable shift to longer wavelengths, making the light warmer although at the cost of a reduced output. LuxLive, November 20, 2013

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