Using the zemax software complex to form photometricmodels of LED illuminator devices

Using the ZEMAX software complex to form photometric models of LED illuminator devices P.S.Chechurov a)and G.E.Romanova b)St.Petersburg National Research University of Information Technologies,Mechanics,and Optics,St.Petersburg(Submitted October13,2011)Opticheski˘ıZhurnal79,57–60(May2012)This paper discusses a method for formingfiles in the IES and LDT formats for LEDilluminator devices,based on the use of the ZEMAX modelling medium.Thefile structure andthe means of modelling the components of the optical part of the device are considered.Aprocess is demonstrated for forming IES and LDTfiles,using as examples an industrial-typelightingfixture and afloodlight projector.The results of calculations carried out in theillumination-engineering program DIAL UX are compared with the use of models obtained byphotometric measurements and modelling in ZEMAX.c 2012Optical Society of America.Today’s illumination-engineering market is undergoing active growth because a large number of LED illuminator devices are appearing in it.As the efficiency of LED illumination increases,such devices become more and more widespread in architectural,street,technical,and interior lighting.It is impossible today to develop lighting projects without using specialized illumination-engineering programs, the calculations in which use computerized photometric models of illuminator devices.These models are currently based on photometric measurements carried out in specialized laboratories.This method makes it possible to obtain the needed information with a fairly high degree of accuracy,but it has substantial drawbacks:the small number offirms that provide such services,and the high cost of offering them.1Some of the most widely used formats for describing photometric characteristics are the IES and LDT formats.The photometric data of illuminator devices are recorded in the form of text data.The general assumptions and recording rules are stipulated by the IESNA:LM-63-1995standards and the EULUMDAT Photometric Data File Format,respectively.Thefile contents for describing the characteristics of a lighting device can be broken down into three blocks.The first block indicates information on the manufacturer,name, description,and purpose of the device,with supplementary and reference information.The second block indicates the number of radiation sources in the device,its luminousflux, the multiplication factor,the number of polar and azimuthal angles to be described,the overall dimensions of the emitting surface,and the power of the device.The third block describes the distribution and value of the device’s luminous intensity.It indicates the luminous intensity for all the polar angles at each azimuth.2,3The luminous intensities can be determined by using the ZEMAX software5in the nonsequential mode of the ray path.This regime is the most suitable for calculations of illuminator optics.It is obvious that the luminous-intensity distribution of the device will be affected by its optical part,consisting of the light source and the illumination-engineeringfittings used to form the required light distribution.Thefittings in17.614.41.37883.27.612.1yout of reflector(sizes in centimeters).LED devices ordinarily use optics that consist of lenses, reflectors,and scatterers.It is these components that need to be modelled to obtain the necessary information.Let us consider the modelling process in more detail,using as an example an industrial-type LEDfixture(ITLF)and an LEDfloodlight projector(LEDF).The ITLF uses two arrays of thirty Cree MX-6LEDs each. Reflectors mounted on each LED are used in thefixture to form the necessary luminous-intensity distribution.The layout of an individual reflector is shown in Fig.1.To determine the illumination-engineering characteristics of the device,it is necessary to model the light sources,the reflectors,and the protective glass.Figure2shows the component editor for modelling a lightingfixture.The models represented on the manufacturers’Web sites can be used to model the LEDs.As a rule,they have DAT, LDT,and IES formats.The DAT format is used in our case. When the sources are being modelled,it is necessary to indicate their parameter set:the coordinates,the number of rays to be mapped and analyzed,and the luminousflux.The number of rays to be analyzed affects the ray-tracing time and the accuracy of the result.The specified parameters can be seen in Fig.2.The illumination-engineeringfittings can be modelled in various ways.For example,if secondary optics are involved,it is convenient to use technicalfiles of format STEP and IGES or to use LDT and IESfiles,which describe the photometric characteristics of the LED–lens system.If reflectors or scatterers are involved,standard methods for modelling inponent editor for modelling a lightingfixture.509840783059203910200L u m i n o u s i n t e n s i t y , c d–90–72–54–36–1801836547290Angle, degFIG.3.Graph of the luminous-intensity distribution of a lighting fixture.ZEMAXcan be used.In an ITLF,the illumination-engineeringfittings are formed by reflectors.Structurally,these are two truncated cones (Fig.1).To model them,we use two standard “cone”objects.To obtain the necessary shape of the reflector,its structural parameters are determined:the properties of the object include its reflectance.The protective glass of an illuminator device is specified by the standard resources of the ZEMAX package.Its main parameters are the material and the length,height,and thickness.The parameters of the protective glass are shown in Fig.2.The last object of the modelling is the radiation detector.It makes it possible to estimate the luminous-intensity distribution of the device or the illuminance at various distances.To do this,we specify the following parameters:the distance to the system,the size,and the number of pixels (seeFig.2).The number of pixels affects the accuracy and time of the tracing.After the illuminator device is modelled,ray tracing is carried out.The tracing time depends on the number of objects in the system,the number of rays to be analyzed,the number of pixels on the detector,and the computer throughput.Figure 3shows a graph of the luminous-intensity distribution,obtained as a result of ray tracing through the modelled system.The ZEMAX software complex supports the introduction of the results into files of IES and LDT formats.These results and the necessary data are supplemented in accordance with the standards IESNA:LM-63-1995and EULUMDAT Photometric Data File Format.2–4Secondary lenses are very often used in LED devices to form the necessary radiation distribution.Let us consider the modelling of such a device,using a projector as an example.An LEDF is intended for outdoor lighting of territories or objects.A subassembly of XP-G LEDs is mounted in it,each of the LEDs being equipped to form the required luminous-intensity curve with a secondary CXP SQUARE SMOOTH SPOT lens.6To determine the illumination-engineering characteristics of the projector,it is necessary to model the light sources,the secondary lenses,and the protective glass.Figure 4shows the component editor for modelling a projector.In this case,technical files of LDT format were used to model the LEDs and the secondary lenses.These files were obtained from the lens manufacturer and describe the light distribution of the Cree XP-G LED with a CXP-SS lens.As when modelling a lighting fixture,theircoordinates,ponent editor for modelling a projector.3.416.811.021.361.70L u m i n o u s i n t e n s i t y , c d–90–72–54–36–1801836547290Angle, degFIG.5.Graph of the luminous-intensity distribution of an LEDF.luminous flux,number of reflectors,and rays to be analyzed were specified.The protective glass and the radiation detector were specified in the same way as in the preceding case.After the rays are traced,we get the luminous-intensity distribution of the projector shown in Fig.5.These results and the necessary data are supplemented in accordance with the standards IESNA:LM-63-1995and EULUMDAT Photometric Data File Format.2–4During the modelling and formation of the IES and LDT files of the lighting fixture and the projector,a question arises concerning the accuracy of this modelling.To answer it,photometric measurements were made in a certification laboratory.IES files were obtained from these measurements.Figure 6shows a comparison of the calculations carried out in the DIAL UX illumination-engineering program,using the IES files of the lighting fixture and the projector,obtained by modelling in the ZEMAX program and by photometric measurements.The results of the calculation using the IES files obtained by modelling in ZEMAX and by photometric measurements are virtually identical;consequently,the error of the method is small.This article has discussed a method of forming com-puterized photometric models of LED illuminator devices by modelling in the ZEMAX medium.It allows files of IES and LDT format to be formed with a description of the illumination-engineering characteristics of the device without55555555555555101010101010101010101010101010101010105050505050505050505050505050505050505050505010010010010010010010010010010010010010010010010010010010010010015015015015015015015015015015015015015015015015015015015015015015015015015015015015010101010101010101010101010102020202020202020202020202020202020202020203030303030303030303030303030303030303030303035353535353535354020ITLF (mounting height 20 m)ModellingModelling MeasurementsMeasurementsLEDF (mounting height 5 m)parison of the results of calculations (program DILAL UX and field measurements for an ITLF and an LEDF.The region of measurements is on a 10×10-m illuminated surface.making photometric measurements.This method has small error and can be used by LED lighting manufacturers.a )Email:ChechurovPS@b )Email:romanova g e@mail.ru1Yu.B.A˘ızenberg,ed.,Illumination Engineering Handbook (Znak,Moscow,2006).2Standard IESNA:LM-63-1995.3ELUMDAT Photometric Data File Format.4ZEMAX Users’Knowledge Base [Electronic resource],ZEMAX:SoftwareFor Optical System Design Down-loads/Support/Knowledge Base.Access to file /kb/.5ZEMAX Optical Design program:User’s Guide,2009.6DataSheet CXP-G [Electronic resource],Access to file /datasheets/DataSheet CXP-G.pdf .。