University of Santo TomasCOLLEGE OF ARCHITECTURE

A Report Submittal on

BUILIDING UTILITIES 3ACOUSTICS AND LIGHTING SYSTEMS

Module No. 1A.) AVERAGE ILLUMINANCE1.) Zonal Cavity by Approximation2.) Pont Source Method3.) Line Source MethodB.) AVERAGE LUMINANCE

By:Group No. 16Bautista, KielBriones, Ashley KeiVillalobos, Jayra28 October 2014

TABLE OF CONTENTS1. AVERAGE ILLUMINANCE1.1. Zonal Cavity Calculation by Approximation1.2. Point Source Method1.3. Line Source Method2. AVERAGE LUMINANCE3. GLOSSARY OF TERMS4. BIBLIOGRAPHY

Zonal Cavity Calculation by Approximation For a first approximation, make the following assumption:

Assume all rooms are square. To do this for a rectangle take one-third the difference in dimensions and add to the smaller dimension to obtain equivalent width. Then for square rooms:RCR = Where:RCR = Room Cavity RatiohRC = Height of Room CavityW = width

Example:A regular classroom whose length is six meters (6.00m), its width eight meters (8.00m), and its height three and seven tenth meters (3.70m) has an initial ceiling reflectance of eighty percent (80%); initial wall reflectance of fifty percent (50%); an initial floor reflectance of twenty percent (20%). Find the room cavity ratio using zonal cavity by approximation.Solve:cc (percent effective ceiling cavity reflectance) = 70w (percent wall reflectance) = 50fc (percent floor reflectance) = 20RCR =(10 x 1.95)/(6+2/3) = 2.93Note: 1.95 (hRC) is derived by subtracting the sum of the floor cavity and ceiling cavity from the total height of the room. Because the room is rectangular, one must add a third of difference of width eight meters (8.00m) and length six meters (6.00m) to the shorter dimension which is six meters (6.00m). This explains the denominator 6 + 2/3 From the table containing coefficients of utilization for typical luminaires with suggested maximum spacing ratios, one arrives at a CU of 0.52 (RCR 3 is used because an RCR of 2.93 is rounded-off).

Solve for the number of fixtures UsingNo. of Luminaires = to get:No. of Luminaires = 753.2 (6mx8m)/ 2(3725)(0.52)(0.55)= 16.96 ~ 17 fixturesCavity Reflectance and IlluminanceIt is important to note that the reflectance of different room cavities have bearing on the coefficient of utilizationFor obvious reasons, ceiling cavity reflectance has more substantial effect with the indirectly distributed light, while floor reflectance has a more profound effect on directly distributed lightsThis especially calls for careful consideration in choosing the interior finishes as unexpected scenarios may require prricy renovations or alterations.LIgthing Calculation - Point Source Method Point Source Method The Point Method is applicable to light emitting from small point sources. The general rule of thumb is the Point Method can be used if and only if the distance from the source is AT LEAST five times the maximum dimension of the source. The latter dimension includes any associated reflector or diffuser

The Point Method makes use of below formula:

HORIZONTALVERTICAL

Using DE = cosE =

Using HE = E =

It is important to note that when several luminaires contribute light to the point of interest, they must be computed for separately and then added together to obtain the net illuminance level.ADVANTAGES: Easily applicable to areas in which point sources, such as incandescents and HID, are involved and no surface reflectance are accounted for.DISADVANTAGE: This cannot be applied to area luminaires such as fluorescent lamps

SAMPLE PROBLEM1. An accent fixture recessed into a 10 ft. ceiling directly above a plate that is on a table at 3 ft. above the floor. If that accent fixture has a center beam candle power (CBCP) of 10,000 candelas, what illuminance level can we expect at the brightest point on the plate?Unknown Value: Illuminance (E)Given Values: Luminous Intensity (I); Distance (D); Note: If surface of interest (the plate) is directly below the source, the angle of incidence may be omitted.2. An accent fixture recessed into a 10 ft. ceiling aimed to light a bust resting on a pedestal 3 ft. from the floor. To accent the bust, the luminaire is aimed at an angle. Aiming the luminaire creates an angle of 30o between the aiming line of the luminaire and the line perpendicular to the plate. If we want to illuminate the plate to 100 foot-candles, what kind of center-beam value would we need from the luminaire?Unkown Value: Luminous intensity (I)Given Values: Illuminance Level (E); Distance (D);Angle ;

Line Source MethodBecause the point method is applicable to light sources whose over-all dimension is less than one-fifth of the distance to the surface, quite a few light sources will be rendered difficult to compute, especially in practical applications.For instance a fluorescent lamp (approximately 4 ft. in length) or a 4 x 4 ft. diffuser fixture would require a 20 ft. distance from a source. For obvious reasons, not all scenarios meet this standard. The Line Method is conducted to compute for the Illumination level of fluorescent fixtures and luminaires alike.Generally, manufacturers provide data regarding the distribution of fluorescent lighting in a room. An illustration below is an example.

However, if one wishes to compute for illuminance level E himself, the below formula must be used:

fc = Illumination at distance D in foot candlesfL = Source brightness in footlambertsD = Distance in feetW = Width of source

Average Illuminance It is important to know the average luminance of, say, the ceiling cavity, in order to identify the contrast between luminous objects and its ceiling background.Make use of the formula: For average initial wall luminance(cd/m2),

Lw

For average initial ceiling cavity luminance(cd/m2) Lcc

Sample Problem:Refer to the given data from the sample problem under zonal cavity method by approximation. Find the average initial wall luminance.Solve:

*value of as well luminance coefficient 0.22 is normally stated by manufacturers.

GLOSSARY OF TERMSAverage Illuminance average the luminous flux incident on unit area of a surface.Average Luminance average luminance of a body, apart from its hue or saturation, that an observer uses to determine the comparative luminance of another body.Point Method Method of finding average illuminance in which a sources maximum dimensions are at most 20% of the distance to the surface.Line Method Method of finding average illuminance in which light source assumes the form of a line instead of a single point.Coefficient of Utilization is a measure of the efficiency of a luminaire in transferring luminous energy to the working plane in a particular area.

BIBLIOGRAPHYhttp://books.google.com.ph/books?id=60MgT86MVvlC&pg =PA515&DQ=calculation+for+line+sources+ illuminance&hl=en&sa=X&ei+ubZDVNixMubSmAWZ4YGYCA&ved=9CCUQ6AEwAA#v=onepage&q=calculation%20for%20line%20sources%20illuminance&f=falsehttp://books.google.com.ph/books>id=ZldvdyPMhl8C&pg=PA660&dq=calculation+for+line+sources+illuminance&hl=en&sa=X&ei=ubZDVNixMubSmAWZ4YGYCA&ved=0CCwQ6AEwAQ#v=onepage&q&f=falsehttp://eilv.cie.com.at/term/583http://www.kodak.com/cluster/global/en/consumer/products/techInfo/am105/am105kic.shtmlhttp://www.schorsch.com/kbase/glossary/luminance.htmlhttp://books.google.de/books?id=ykk1xQc25c0C&pg=PA449Mechanical and Electrical Equipment for Buildings by Stein, Kwok, Gronzdik