A theoretical comparison between batwing and lambertian distributions of power LEDs related to an interior lighting system

Transcription

1 A theoretical comparison between batwing and lambertian distributions of power LEDs related to an interior lighting system GABRIEL ISPAS Electrical and Lighting Department Faculty of Building Services Engineering Technical University of Civil Engineering Bucharest Bd. Pache Protopopescu nr. 66, sector 2, cod ROMANIA Abstract: - This papers deals with power LEDs used as individual luminaires in order to create proper interior lighting systems for fulfilling normal activities. This approach takes into account the fact that, at least for some of the power LEDs on the market, manufacturers provide not only one, but two or even three different luminous intensity distributions. Thus, depending on the type of the luminous intensity distribution, lighting system features will vary from case to case, allowing the choice of the optimal solution for a given situation. Key-Words: - power LEDs, batwing, lambertian, emitter, luminous flux, luminous intensity 1 Introduction An important feature of power LEDs from various manufacturers is that some constructive types of such LEDs can be supplied to the market in many types of distribution of luminous intensity. [1], [2] Based on this idea, the author thinks that the built-in power LED geometry allows the designer to consider power LED itself to be a real luminaire which is part of a lighting system configuration. Thus, using some lighting software, it is possible to make a theoretical analysis of lighting system equipped with various types of power LEDs, highlighting the advantages and the disadvantages involved by a certain solution in relation to another one and to assess what type of lighting system (and what type of distribution of the power is most favorable for a given situation. In order to be allowed to use lighting computer programs, it is necessary for each type of power LED to be stored within a standardized database. Thus, the Eulumdat and IESNA files related to the two types of power LEDs were established as shown in [2]. Luminous intensity distribution curves in polar coordinates corresponding to the above mentioned power LEDs are given in fig. 1 and fig Problem Formulation The paper suggests to use for this study two types of Luxeon power LED emitters range, as follows: - a perfect diffuse (lambertian) distribution type (code LXHL-PW02); - a batwing distribution type (code LXHL-BW02). For a junction temperature of 25 0 C, the nominal luminous flux emitted is the same for both power LEDs, namely 45 lm. Besides, both of them emit a white color of 5500 K nominal color temperature (cool white). Fig. 1 Luminous intensity distribution curve for LXHL-PW01 lambertian Luxeon emitter (power ISBN:

2 Working plane will be also considered at 0,85 m up the floor. For this section the Dialux Professional will be used as lighting software and the normalized lighting files will be of IESNA format. [2] Fig. 2 Luminous intensity distribution curve for LXHL-BW02 batwing Luxeon emitter (power 2.1 General and uniform lighting system, based on power LEDs uniformly and symmetrically distributed. Illuminance levels variation Running the Relux Professional lighting software (using the Eulumdat files of the power LEDs), it is possible to get the required number of individual power LEDs for reach the average illuminance levels from 10 lx to 200 lx, with incrementing steps of 10 lx. For this purpose, the author takes into account a rectangular room with dimensions LxWxH = 5 m x 4 m x 2,7 m and reflectances of the ceiling, walls and the floor are considered to be 0,70, 0,50 and 0,20 respectively. Working plane shall be deemed located at a height of 0,85 m from the floor. [2] 2.2 General and uniform lighting system, based on power LEDs concentrically and symmetrically distributed. Illuminance levels variation In this case the power LEDs are not positioned individually, but equidistantly on a circular contour, forming a fictional luminaire of 20 cm diameter and consisting of 10 power LEDs. The computation room will keep its shape and size (rectangular room with dimensions LxWxH = 5 m x 4 m x 2,7 m and reflectances of the ceiling, walls and the floor are considered to be 0,70, 0,50 and 0,20 respectively). 2.3 General and uniform lighting system, based on power LEDs uniformly and symmetrically distributed. Illuminance uniformity in relation to reflectances Within this chapter the photometric files will be of Eulumdat type, and the proper software will be Dialux Professional. In this case the reflectance values will not be kept unchanged, but they will become variable. It aims to establish how variation of this reflectances affects illuminance uniformity. During calculations, the room geometry keeps unchanged. [2] 3 Problem Solution 3.1 General and uniform lighting system, based on power LEDs uniformly and symmetrically distributed. Illuminance levels variation In order to achieve tangible results, a total number of 80 Relux files were processed. First, it must be established the dependence between average values of the illuminance (horizontal on the workplane - Emh, vertical on the longitudinal Emvl and transversal walls Emvt) and the total number of power LEDs, as shown in figures 3 and 4. The illuminance level increases with the number of power LEDs, but this growth is more pronounced for the Emh than for Emvl or Emvt, which have both approximately the same slope. Meanwhile, the slopes are more pronounced for lambertian distribution than those for the batwing one. Regarding the illuminance level on the workplane (Emh), in order to achieve an average value of 177 lx, a number of 144 power LEDs with batwing distribution are required, compared to 169 power LEDs with lambertian distribution which are required to obtain 188 lx. According to the data of [2], it can be concluded that, at least for illuminance levels over 150 lx, the batwing distribution is more efficient than the lambertian one, in terms of Emh. ISBN:

3 Further analysis (whose graphical representations are shown in fig. 5 and fig. 6) refers to the dependence of the uniformity of the illuminance (by considering the coefficients g1h, g2h, g1vl, g2vl, g1vt and g2vt as defined below) on the total number of power LEDs. For the workplane: g1h=eminh/emh (1) and g2h=eminh/emaxh (2), where Eminh represent the minimum and Emaxh, the maximum values of the horizontal illuminance on the workplane. For the longitudinal wall: g1vl=eminvl/emvl (3) and g2vl=eminvl/emaxvl (4), where Eminvl represent the minimum and Emaxvl, the maximum values of the vertical illuminance on the longitudinal wall. Fig. 3 Variation Em=f(N) for LXHL-BW02 batwing Luxeon emitter (power Fig. 4 Variation Em=f(N) for LXHL-PW01 lambertian Luxeon emitter (power Fig. 5 Variation g1h,g2h,g1vl,g2vl,g1vt,g2vt=f(n) for LXHL-BW02 batwing Luxeon emitter (power For the longitudinal wall: g1vt=eminvt/emvt (5) and g2vt=eminvt/emaxvt (6), where Eminvt represent the minimum and Emaxvt, the maximum values of the vertical illuminance on the transversal wall. ISBN:

4 Thus, the minimum/maximum values on this range are: for g1vl 0,69/0,52, for g2vl 0,55/0,37, for g1vt 0,69/0,54 and for g2vt - 0,55/0,38. Another important observation is that variations in vertical uniformity are lower than those for batwing distribution. The graphics representing the dependence between the electrical power consumption and the total number of power LEDs are shown in fig. 7 and 8. Fig. 6 Variation g1h,g2h,g1vl,g2vl,g1vt,g2vt=f(n) for LXHL-PW01 lambertian Luxeon emitter (power For batwing distribution, it can be noted that on the workplane, the two coefficients of uniformity values are practically constant (g1h 0,50, respectively g2h 0,36). Regarding the longitudinal and transversal walls, the graphical representations are roughly similar; although up to average proposed illuminance levels on the workplane of 60 lx (corresponding to N=49 power LEDs) there are significant variations (it can be observed two areas of minimum and maximum), above these values the two uniformity coefficients are continuously increasing, following approximately the same slope - g1vl from 0,37 to 0,72, g2vl from 0,28 to 0,56, g1vt from 0,40 to 0,65 and g2vt from 0,30 to 0,49. For lambertian distribution, the two values for the uniformity coefficients on the workplane are practically constant (average values being g1h 0,51, g2h 0,41). Unlike the batwing distribution, graphics for vertical uniformity coefficients on the longitudinal and transversal walls do not stabilize on the entire range (0-200 lx). Fig. 7 Variation P=f(N) for LXHL-BW02 batwing Luxeon emitter (power Based on [2], the conclusion is that each of these two power LEDs consumes, individually, the same electrical power. This means the total electrical consumption will depend only on the total number of LEDs. Thus, taking into account all the observations from Em = f (N) graphics (fig. 3 and 4), in order to achieve the desired values of illuminance, the following electrical power consumption values will be considered: - for batwing distribution, 144 power LEDs will consume a total electrical power of 575 W; - for lambertian distribution, 169 power LEDs will consume a total electrical power of 675 W, i.e. an increase of 17,4% in energy consumption compared to batwing distribution. ISBN:

5 Fig. 8 Variation P=f(N) for LXHL-PW01 lambertian Luxeon emitter (power Fig. 9 Variation Emh=f(N, number of fictional LEDs power luminaires) for LXHL-BW02 batwing Luxeon emitter (power 3.2 General and uniform lighting system, based on power LEDs concentrically and symmetrically distributed. Illuminance levels variation In order to achieve tangible results, a total number of 44 Dialux files were processed. The calculation algorithm is as follows: the Dialux software calculates the illuminance levels and the corresponding uniformity coefficients values on workplane and on ceiling surfaces for each of the two situations (batwing and lambertian distributions), taking into account that the lighting system consists of : 1, 2, 4, 6, 8, 9, 12, 16, 20, 25 and respectively 30 fictional luminaires as described in chapter 2.2, which are placed symmetrically on the ceiling. Thus, for batwing distribution, figure 9 shows that the Emh on the workplane increases approximately constant up to 122 lx (corresponding to a total of 90 power LEDs grouped within 9 luminaires); after this threshold, the average illuminance value is more pronounced increasingly, reaching 402 lx for 300 power LEDs grouped in 30 luminaires. Fig. 10 Variation Emh=f(N, number of fictional LEDs power luminaires) for LXHL-PW01 lambertian Luxeon emitter (power ISBN:

6 By comparison, for lambertian distribution, figure 10 shows that the average horizontal illuminance value on the workplane increases approximately constant up to 113 lx (corresponding to a total of 90 power LEDs grouped within 9 luminaires); after this threshold, the average illuminance value is more pronounced increasingly, reaching 370 lx for 300 power LEDs grouped in 30 luminaires. For batwing distribution, illuminance uniformity increases significantly up to 56 lx (corresponding to 40 power LEDs), the values of the two uniformity coefficients being g1h=0,68, respectively g2h=0,40; further, g2h coefficient remains practically constant - average value, 0,42, and g1h drops to the corresponding value of 82 lx (6 fictional luminaires), then keeps a constant average value, around 0.59 (fig. 11). representations flatten - g1h = 0,62, respectively g2h = 0,50 (fig. 12). Fig. 12 Variation g1h,g2h=f(n, number of fictional LEDs power luminaires) for LXHL-PW01 lambertian Luxeon emitter (power Fig. 11 Variation g1h,g2h=f(n, number of fictional LEDs power luminaires) for LXHL-BW02 batwing Luxeon emitter (power For lambertian distribution, illuminance uniformity increases significantly up to 52 lx (corresponding to 40 power LEDs), the values of the two uniformity coefficients being g1h=0,60, respectively g2h=0,48; then, both g1h and g2h coefficients are slightly descending, down to 199 lx (which corresponds to 16 fictional luminaires); after that, both graphical Regarding the batwing distribution, in terms of average horizontal illuminance on ceiling plane (fig. 13), it increases approximately constant up to a value of 27 W (corresponding to a total of 90 power LEDs grouped in 9 fictional luminaires); after that, its increasing is more pronounced, reaching 92 lx for 300 power LEDs (grouped within 30 fictional luminaires). On the other hand, the two graphs of variation of the uniformity coefficients (fig. 13) have a similar slope, allowing the identification of four distinct areas: two areas of constancy (from 0 to 2 and from 4 to 9 fictional luminaires), a pronounced increase area (from 2 to 4 such luminaires) and a less pronounced increase area (from 9 to 30 fictional luminaires, mentioning that from 20 luminaires away, the graphical representation of both uniformity coefficients tend flattening). The maximum / minimum values of these uniformity coefficients are: for g1hceiling 0,86 / 0,62 and for g2hceiling 0,79 / 0,50. ISBN:

7 Fig. 13 Variation Emhceiling=f(N, number of fictional LEDs power luminaires) for LXHL-BW02 batwing Luxeon emitter (power Concerning the lambertian distribution, in terms of average horizontal illuminance on ceiling plane (fig. 15), it increases approximately constant up to a value of 30 lx (corresponding to a total of 90 power LEDs grouped in 9 fictional luminaires); after that, its increasing is more pronounced, reaching 48 lx for 160 power LEDs (grouped within 16 fictional luminaires). Within third area, between 16 and 30 luminaires, the slope of the illuminance increases is even more pronounced, so that at the end of this range the corresponding value of the average horizontal illuminance on ceiling is 104 lux. Unlike batwing distribution, the two graphical representations of the variation of the uniformity coefficients (fig. 16) are very different. Thus, g2ceiling is continuously increasing, from 0,02 up to 0,45 at the end of the range, while g1ceiling increases from minimum (0,62, corresponding to 10 power LEDs) up to the corresponding value of 120 power LEDs, grouped in 12 fictional luminaires (0,87), then remains nearly constant or even decreases slightly (0,86 for 300 power LEDs, grouped in 30 fictional luminaires). Fig. 14 Variation g1hceiling,g2hceiling=f(n, number of fictional LEDs power luminaires) for LXHL-BW02 batwing Luxeon emitter (power Fig. 15 Variation Emhceiling=f(N, number of fictional LEDs power luminaires) for LXHL-PW01 lambertian Luxeon emitter (power ISBN:

8 of (minimum value, 0,44, for 10 lx and maximum value, 0,50, for 200 lx), (minimum value, 0,48, for 10 lx and maximum value, 0,55, for 150 and 200 lx) and (minimum value, 0,48, for 10 lx and maximum value, 0,57, for 150 lx). On the contrary, the maximum values for g1h coefficient occur, regardless the illuminance level, for triplets ρceiling-ρwalls-ρfloor of (0,60 constant value), (minimum value, 0,56, for 10 lx and maximum value, 0,61, for 100 and 150 lx) and (minimum value, 0,58, for 10 lx and maximum value, 0,61, otherwise). Fig. 16 Variation g1hceiling,g2hceiling=f(n, number of fictional LEDs power luminaires) for LXHL-PW01 lambertian Luxeon emitter (power 3.3 General and uniform lighting system, based on power LEDs uniformly and symmetrically distributed. Illuminance uniformity in relation to reflectances In order to achieve tangible results, a total number of 120 Dialux files were processed. The calculation algorithm is as follows: For each of the illuminance values of 10, 50, 100, 150 and 200 lx, the reflectances of ceiling, walls, floor (mandatory in that order) will be changed, as a percentage, in this way: , , , , şi The goal is to calculate the uniformity coefficients on the workplane (g1h, g2h) for both distributions: batwing and lambertian. In terms of batwing distribution, regarding the uniformity coefficient of the illuminance on the workplane - g1h figure 17 shows that, generally, its values increase with illuminance levels. Its minimum values occur, regardless the illuminance level, for triplets ρceiling-ρwalls-ρfloor Fig. 17 Variation g1h=f(e,ρceiling-ρwalls-ρfloor) for LXHL-BW02 batwing Luxeon emitter (power Fig. 18 Variation g2h=f(e,ρceiling-ρwalls-ρfloor) for LXHL-BW02 batwing Luxeon emitter (power ISBN:

9 Regarding the uniformity coefficient of the illuminance on the workplane g2h figure 18 shows that its values also generally increase with illuminance levels. Its minimum values occur, regardless the illuminance level, for triplets ρceiling-ρwalls-ρfloor of (minimum value, 0,29, for 10 lx and maximum value, 0,34, for 200 lx), (minimum value, 0,33, for 10 lx and maximum value, 0,39, for 150 and 200 lx) and (minimum value, 0,35, for 10 lx and maximum value, 0,40, for 150 lx and 200 lx). On the contrary, the maximum values for g2h coefficient occur, regardless the illuminance level, for triplets ρceiling-ρwalls-ρfloor of (minimum value, 0,40, for 10 lx and 0,44, otherwise), (minimum value, 0,39, for 10 lx and 0,44, otherwise) and (minimum value, 0,40, for 10 lx and maximum value, 0,45, for 100 and 200 lx). In terms of lambertian distribution, regarding the uniformity coefficient of the illuminance on the workplane - g1h figure 19 shows that, generally, its values increase with illuminance levels. Its minimum values occur, regardless the illuminance level, for triplets ρceiling-ρwalls-ρfloor of (minimum value, 0,47, for 10 lx and maximum value, 0,55, for 200 lx), (minimum value, 0,56, for 10 lx and maximum value, 0,60, for 200 lx) and (minimum value, 0,57, for 10 lx and maximum value, 0,60, for 150 and 200 lx). On the contrary, the maximum values for g1h coefficient occur, regardless the illuminance level, for triplets ρceiling-ρwalls-ρfloor of (minimum value, 0,59, for 10 lx and maximum value, 0,64, for 50 lx), (minimum value, 0,62, for 10 lx and maximum value, 0,64, for 100 lx) and (minimum value, 0,63, for 50 and 200 lx and maximum value, 0,64, otherwise). Regarding the uniformity coefficient of the illuminance on the workplane g2h figure 20 shows that its values also generally increase with illuminance levels. Its minimum values occur, regardless the illuminance level, for triplets ρceiling-ρwalls-ρfloor of (minimum value, 0,37, for 10 lx and maximum value, 0,41, for 200 lx), (minimum value, 0,42, for 10 lx and maximum value, 0,46, for 150 and 200 lx) and (minimum value, 0,44, for 10 lx and maximum value, 0,46, for 100, 150 and 200 lx). On the contrary, the maximum values for g2h coefficient occur, regardless the illuminance level, for triplets ρceiling-ρwalls-ρfloor of (minimum value, 0,50, for 10, 150 and 200 lx and 0,51, otherwise), (minimum value, 0,49, for 10 lx and 0,51, for 50 and 100 lx) and (minimum value, 0,51, for 10, 100, 150 and 200 lx and maximum value, 0,52, for 50 lx). Fig. 19 Variation g1h=f(e,ρceiling-ρwalls-ρfloor) for LXHL-PW01 lambertian Luxeon emitter (power Fig. 20 Variation g2h=f(e,ρceiling-ρwalls-ρfloor) for LXHL-PW01 lambertian Luxeon emitter (power ISBN:

10 4 Conclusion As a synthesis, it can be concluded that: - power LEDs characterized by batwing distribution are more economical and the illuminance uniformity on the workplane is good (although g1h and g2h values are, however, lower than the corresponding values for lambertian distribution); vertical illuminance uniformity is good (especially at high illuminance levels) and illuminance uniformity on the ceiling is better than the lambertian one. - power LEDs characterized by lambertian distribution are less economical than the batwing distribution ones; instead, vertical uniformity is better, even at low illuminance levels; illuminance uniformity on the workplane is better, but it becomes worse in terms of ceiling illuminance uniformity. Table 1 summarizes the main advantages and disadvantages (by comparison) between power LEDs characterized by batwing, respectively lambertian distributions of the luminous intensity. Table 1. Main advantages and disadvantages of power LEDs characterized by batwing, respectively lambertian distributions of the luminous intensity (by comparison) References: [1] Bianchi, C., Mira, N., Moroldo, D., Moroldo, H., Ispas, G., ş.a, Enciclopedia tehnică de instalaţii electrice, ed. a II-a, Editura Artecno, Bucureşti, [2] Ispas, G., Contribuţii la studiul sistemelor de iluminat interior specializate echipate cu diode electroluminescente ( teză de doctorat, Universitatea Tehnică de Construcţii Bucureşti, Facultatea de Instalaţii, [3] Philips Lumileds., Inc., Application Brief AB07, Lumen Maintenance of White Luxeon Power Light Sources. [4] Philips Lumileds., Inc., Application Brief AB08, Optical Testing for SuperFlux, SnapLED and LUXEON Emitters. [5] Philips Lumileds., Inc., Application Brief AB10, LUXEON Emitter Assembly Guide. [6] Philips Lumileds., Inc., Application Brief AB11, Electrical Drive Information for Luxeon Products. [7] Philips Lumileds., Inc., Application Brief AB15, LUXEON Benefits Over Competitive LED Products. [8] Philips Lumileds., Inc., Application Brief AB17, Benefits of Lumileds Solid State Solutions vs. Conventional Lighting. [9] Philips Lumileds., Inc., Application Showcase AS03, Architectural Detail Lighting. [10] Philips Lumileds., Inc., Application Showcase AS13, LED Retrofit Lamps. [11] Philips Lumileds., Inc., Brochure BR02, Lumileds Application Overview. [12] Philips Lumileds., Inc., Brochure BR04, 10 Myths About LEDs, and the Luxeon Difference. [13] Philips Lumileds., Inc., Environmental Data ED16, Luxeon I Star Batwing Materials Declaration Form (IPC ). [14] Philips Lumileds., Inc., Environmental Data ED17, Luxeon I Star Lambertian Materials Declaration Form (IPC ). [15] Philips Lumileds., Inc., Reliability Data RD25, LUXEON Reliability. [16] Philips Lumileds., Inc., Technical Datasheet DS23, Luxeon Star Technical Datasheet. [17] Philips Lumileds., Inc., Technical Datasheet DS23A, Luxeon Star Option Code Selections. [18] Philips Lumileds., Inc., Technical Datasheet DS25, Power Light Source Luxeon Emitter [19] Philips Lumileds., Inc., Technical Datasheet DS25A, Luxeon Emitter Option Code Selections [20] Philips Lumileds., Inc., Technical Presentation TP35, White Lighting (Illumination) with LEDs ISBN: