Dependence of the Color Rendering Index on the Luminance of Light Sources and Munsell Samples

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1 Australan Journal of Basc and Appled Scences, 4(10): , 2010 ISSN Dependence of the Color Renderng Index on the Lumnance of Lght Sources and Munsell Samples 1 A. EL-Bally (Physcs Department), 2 M.M. EL-Ganany, 3 A. AL-Kamel (Photometry Department- NIS) Abstract: In ths work, the relaton between the lghtng levels (lumnance) and the color propertes (color renderng) for both the source and the surroundng represented by the Munsell's sample has been obtaned. From the analyss of the expermental and calculated data one can show that to obtan good vsual performance assocated wth good color renderng, one must choce lamps wth hgher lumnance value n partcular n the case of fluorescent lamp. Key words: Lumnance, Illumnance, specal and general Color renderng, color appearance INTRODUCTION The qualty of any lghtng scheme depends on the vsual performance caused by the llumnaton of the lghtng scheme whch satsfes the followng vsual task requrements. To effectvely reveal the task and the general surroundng by consderng the factors represented n study work as presented by (Prtchard. D.C, 1985) taken (CIBS 1984 lghtng Code) shows how these factors can be related. Such dagram relates vsual performance to llumnance levels for three specfc contrast (C) and angular szes (S). The vsual performance scale s relatve. The prefered color appearance of both source and objects s mportant n connecton wth lghtng level n an nteror. Researches show that atmosphere created n an nteror s generally nfluenced by both the color of the lght used and the brghtness mpresson created by the lght. The color renderng propertes of a source are partcularly mportant n some specal purposes lghtng applcaton. The annual total cost of the lghtng scheme conssts of: The captal cost of the lghtng scheme whch comprses the sum of prces of all the components buldng the scheme (lamps, ballasts, lumnares) addtonal to the runnng cost ncludng electrc power prce, cleanng and mantenance of the scheme per year. MATERIALS AND METHODS Frst: Lghtng levels: When plannng an nteror lghtng nstallaton, the lghtng level should be determned. Such lghtng level can be expressed n terms of the llumnance (E) whch s the lumnous flux ncdent on unt area of a surface, or lumnance (L) of the llumnated surface area, therefore both E&L are closely nterrelated. In the case of dffusely reflectng surface, the equaton connectng these two quanttes s L E (1) s the coeffcent of dffused reflecton of the llumnated surface. So the quanttes E and L are referred as lghtng level Dfferent types of nteror needed dfferent lghtng levels sutable to valdate vsual performance or vsual satsfacton crteron. Correspondng Author: M.M.EL-Ganany, (Physcs Department), E-mal. alkamel_ns@yahoo.com 4609

2 Fg. 1: The relaton between vsual performance and llumnance for task szes Prefered Illumnance Values: The results of frst nvestgatons whch have been carred out by dfferent workers wth the object of establshng preferred horzontal llumnance levels are lsted n Table. 1 (J.B.de Boer& D.Fscher, 1978) Table 1: Horzontal llumnance levels Auther and reference year Number of observer Range of llumnance Balder Muck and Bodman Investgaton (a) Muck and Bodman Investgaton (b) Sollner Remenschneder Investgaton (a) Remenschneder Investgaton (b) Westhoff and Horeman Boeey Bodmann. Sollner and Vot The Color Appearance: The CIE techncal commttee on general color renderng ndex R a therefore developed a method that rates lamps n terms of general color renderng ndex R a (CIE 1965 and 1974) (CIE, 1965,). The method s based on the average color shft of a number of test colors samples for whch the color appearance wll change when changng from test to reference llumnant. It was concluded that a seres of eght test colors could be consdered suffcent for use n descrbng the general color renderng ndex of the lamps. The eght fnally selected test colors are that of the Munsell samples whch has the notaton as n Table. 2. (CIE, 1965,). Table 2: The eght fnally selected test colors are that of the Munsel samples No. Munsell notaton Color appearance under daylght 1 10P6/8 Lght reddsh purple 2 2.5P6/ 8 Lght volet 3 5PB6/ 8 Lght blue 4 10BG6/ 4 Lght blush green 5 2.5G6/ 6 Moderate yellowsh green 6 5GY6/ 8 Strong yellow green 7 5Y6/ 4, Dark graysh yellow 8 7.5R 6/ 4 Lght graysh rednote: Such colored samples could be representng the colors of the surroundng n an nteror. 4610

3 To calculate the color shft E of the Munsell samples that take place when changng from test to reference llumnant, one should calculate tr-stmulus values and the color coordnates for both the source and Munsell samples. The specal color renderng ndex R for each Munsell sample s gven by formula (2) (CIE, 1964). R E Where E s the color shft of th Munsell sample The general color renderng ndex s calculated from the frst eght R values as ther arthmetc mean (2) R a R 1 (3) Expermental: The Ocean optcs HR200 Spectroradometer used for determnng the spectral power dstrbuton and color parameters need for calculatng the color renderng ndces for dfferent lght sources. The lumnance of dfferent lamps used n lghtng has been measured usng Mnolta CS-1000A lumnance meter. The measured lamps are that mentoned n table 3. The accuracy of measurements used such meter s + 2 %. The expermental values of the lumnance for dfferent lamps are llustrated n table 3. The system structure for measurng lumnance llustrated n Fg.2. Table 3: The expermental values of the lumnance for dfferent lamps Lamp type Lumnance Color renderng 100 W ncandescent lamp W ncandescent lamp W daylght fluorescent lamp W warm whte fluorescent lamp WSupper tr-phosphor Fluorescent lamp W warm whte savng energy lamp Fg. 2: The system structure for measurng lumnance Calculatons: Determnaton of the tr-stmulus values X k,, Y k,, Z k, for the test color Samples llumnated by the lght source to be tested k. X k, =K S l (l) (l) (l)dl (4) x 4611

4 Y k, =K S l (l) (l) (l)dl (5) y Z k, =K S l (l) (l) (l)dl (6) z Where K s the maxmum spectral effcacy = 683 lm /watt (V.V. Meshkove, 1981), S () s the relatve spectral power of an llumnant. () s the spectral reflectance or transmttance of the th sample, y z (l), (l) are the color matchng functon (CIE,1931) Note: the value of the Y k, s expressed n percent and s the photometrc transmttance or reflectance of the sample (Casmer De Cusats, 1997). Hence consderng certan value of llumnance (E), the value of lumnance for each Munsell sample L can be gven by the formula L. EY k, In ths work we consder E = 500 Lux, then usng the above mentoned equaton for calculatng R and L, the results of calculaton llustrated n Table 4. Table 4: The lumnance of the Munsell samples Source type Sample1 Sample2 Sample3 Sample4 Sample5 Sample6 Sample7 Sample8 150w ncandescent lamp L R Daylght 40w Fluorescent lamp L R Warm whte Fluorescent lamp L R Supper trphosphor lamp L R Energy savng Fluorescent lamp L R W blended lamp L R Dscusson: More recent research (Bellchambers) has shown that the color renderng of the lamp s lnked wth llumnance n determnng what has been called the vsual clarty of our surroundng whch descrbes the satsfacton of appearance; But the lnk between the color renderng ndex and the lumnance s absent n lterature n spt of the fact that both R a and L dependng on the spectral power dstrbuton of the sources and the spectral reflectance of llumnated surroundngs. An observer's feld of vew n an nteror may nclude some or all of followng: (faces, a task area, walls, celng, sky seen through a wndow), lumnares. As the Munsell sample represents the surroundng of dfferent color, then from Table.4.and referrng to (J.B.de Boer&.D.Fscher, 1978) one can conclude the followng: - The mnmum values of L can be acheved for all objects under all type of lamps. - The optmum values of L for wall and celng and for the task area can be acheved usng super trphosphor lamp only n the case of E = 500 Lux. - The optmum value for human features can be acheved f the llumnance s greater than 600 Lux usng the supper trphosphor lamp. - When referrng to the lumnance of sky, the value 2000 cd/m 2 marks the begnnng of glare from the sky or lumnares. - From Table.4. the lumnance of the Munsell samples are relatvely hgh n the case of supper trphosphor lamps. Ths means that the number of such lamps correspondng certan llumnance level wll be relatvely less x (l), (7)

5 Concluson: The data llustrated n Table.3. show that the general color renderng ndex R a of the lght source ncrease wth ts lumnance. As R a s not affected by ncreasng the llumnance, then to acheve good vsual performance assocated wth good color renderng, the ncrease of lghtng level must be obtaned by ncreasng both L and E.e. choosng the sources of relatvely hgh L n the nteror. In the case of fluorescent lamp, t s preferred usng supper trphosphor as L s relatvely hgh. REFERENCES Casmer De Cusats, Optcal Socety of Amerca, Handbook of Appled Photometry, pp: Meshkove, V.V., Fundamentals of llumnaton engneerng, pp: Prtchard, D.C., Lghtng, pp: Prof. J.B.de Boer and Prof. Dr. D. Fscher, Interor Lghtng, pp: The Internatonal Commsson on Illumnaton (CIE) publcaton, Determnaton of the color renderng of lght sources, pp: The Internatonal Commsson on Illumnaton C.I.E publcaton, Color renderng of lght sources The Internatonal Commsson on Illumnaton CIE publcaton, Color matchng functon. 4613

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