PRESENTATION

LIGHTING ILLUMINATION CALCULATION Prepared by : Kunarta D.

1.0 INTRODUCTION The purpose of this presentation is to give a figure how to calculate the illumination level and how many lighting fixtures is required. 2.0 PROCEDURE To select the right lighting fixture for a specific job there is a simple Four-step procedure. The four-step are: 1. 2. 3. 4.

Determine Area Lighting needs Select type of Lamp Select type of lighting fixture Calculate number of lighting fixtures required

3.0 DETERMINE AREA LIGHTING NEEDS To select the proper lighting fixture and determine number of lighting fixture required, the following aspects need to be addressed. A. Determine Illumination quantity required. The Illuminating Engineering Society in the current IES Lighting handbook gives a comprehensive listing of footcandle levels recommended for all types of industrial Lighting.

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TYPE OF ACTIVITY Public spaces with dark surroundings Simple orientation for short temporary visits Working spaces where visual task are only occasionally performed Performance of visual tasks of high contrast or large size

ILLUMINANCE CATEGORY A

RANGES OF ILLUMINANCE LUX FOOTCANDLES 20-30-50 2-3-5

B

50-75-100

5-7.5-10

C

100-150-200

10-15-20

D

200-300-500

20-30-50

Table 1. Interior Categories and Footcandle ranges (From Hubbell Catalog) B. Area Code Depending on materials or atmosphere within an area, the choice of lighting fixture and lamp is therefore somewhat restricted if the area is classified as hazardous. C. Maintenance considerations Atmospheric conditions: Lighting fixture for use in extremely wet location should be enclosed and gasketed. 4.0 SELECT TYPE OF LAMP The following guide can be used in selecting the proper lamp: A.

Illumination level High (30 FC or more): High intensity discharge (HID) lamps are generally the most economic choice. Low (less than 30 FC): all light source can be considered At medium to high mounting, high intensity discharge is generally best. B. Accessibility High intensity discharge lamp should be used where lighting fixtures are relatively inaccessible because of long life and the need for frequent relamping.

C.

Burning hours At more than 2,000 burning hours per year, high intensity discharge and fluorescent lamps generally yield the lowest system cost.

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LAMP ADVANTAGES 1. High Pressure Sodium Long lamp life (24,000 hrs). Highest lamp output. 2. Metal Halide Moderately long lamp life (7,500 hrs). High light output. Makes colors look close to natural. 3. Mercury Long lamp life (24,000 hrs). High light output. 4. Fluorescent Long lamp life (7,500~24,000hrs). High light output. Low brightness. 5. Incandescent Low initial cost.

DISADVANTAGES High initial cost. High initial cost.

High initial cost. High initial cost. Low light output, short lamp light (500~2,000 hrs).

Table 2. Lamp characteristics (From Crouse-Hind catalog) 5.0 SELECT TYPE OF LIGHTING FIXTURE A. Choice of reflector Mounting Height Above Floor Up to 19’ 20’ or more

Reflector Dome High bay

Table 3. Reflectors (From Crouse-Hind catalog) B. Environment Environment Corrosive Explosive Vapors (Cl. I Div 1) Combustable Dusts (Cl II Div 1) Moisture, Non-combustable Dusts or Potential for Hazard vapors Cl I Div 2 Non Hazardous

Non Metallic Enclosed & gasketed Explosion proof Dust Ignition-proof Enclosed & gasketed Enclosed & gasketed

Table 4. Environment (From Crouse-Hind catalog) PRESENTATION OF LIGHTING CALCULATION

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6.0 CALCULATE THE NUMBER OF LIGHTING FIXTURES REQUIRED For uniform lighting of a specific area, the Lumen method is used to calculate the number of lighting fixtures required. This method takes into account not only the direct light from the lighting fixture, but also that which is reflected from the ceiling, walls and floor. The higher the reflectivity of the surfaces, the fewer number of lighting fixtures required. The coefficient of Utilization as used in the calculation makes allowances for light absorbed by walls, floors and ceiling must be estimated. When supplementary lighting(highlighting) or floodlighting is needed use the Point by Point method to determine footcandles at the specific point or points on the work plane. 6.1

LUMEN METHOD

Basic steps in the Lumen method are: a.

Determine Cavity Ratios There are three Cavity Ratios that should be determined, Ceiling Cavity Ratio Room Cavity Ratio Floor Cavity Ratio Each of these ratios can be found through tables from vendor catalog. hcc Fixture plane hrc Work plane hfc

Room Cavity Ratio, 5 hrc (L + W) RCR = -----------------------LxW PRESENTATION OF LIGHTING CALCULATION

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Ceiling Cavity Ratio, 5 hcc (L + W) CCR = -----------------------LxW

Floor Cavity Ratio, 5 hfc (L + W) FCR = -----------------------LxW If we assume hfc and h cc is zero, than we just take RCR in the calculation. b.

Determine Reflectances Effective reflectances of different room cavities are determined in the table from vendor catalog. Typical approximate reflectances: CEILING Standard White Paint Rough White Paint Rough Light Paint

WALLS 80% White paint 50% 30% Rough Light Paint

FLOORS 80% 30%

Dark concrete Carpet average

20% 15%

Table 5. Typical approximate Reflectance. (From Hubbell Lighting catalog) c.

Determine Coefficient of Utilization Coefficient of Utilization(CU) is portion of lamp lumens which reach the work plane. Affected by room proportions and room-surface reflectances. The coefficient of utilization is determined from the CU table.

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Coefficients of Utilization for 20% effective floor cavity reflectance Effective 80 70 50 30 10 ceiling cavity reflectance Wall 50 30 1 5 3 1 5 3 1 50 30 10 50 30 10 reflectance 0 0 0 0 0 0 0 ROOM COEFFICIENTS OF UTILIZATION-ZONAL CAVITY CAVITY 1 75 71 6 7 6 6 6 6 6 65 63 61 62 61 59 8 3 9 6 9 6 4 2 64 59 5 6 5 5 6 5 5 57 53 50 54 51 48 4 3 8 3 0 5 1 3 56 49 4 5 4 4 5 4 4 49 45 41 47 43 40 4 4 8 3 2 7 2 4 48 41 3 4 4 3 4 3 3 43 38 34 41 36 33 6 7 0 5 5 9 5 5 42 35 3 4 3 2 3 3 2 37 32 28 36 31 27 0 1 4 9 9 3 9 6 37 30 2 3 3 2 3 2 2 33 28 24 32 27 23 5 6 0 5 5 9 4

0

0

57 47 38 31 26 22

Table 6. Coefficient of Utilization (From Hubbell Lighting catalog) d.

Determine Light Loss factor Light Loss Factor is depreciation of initial lighting level due to Lamp Lumen Depreciation and accumulation of dirty on lamp and fixture surface. LAMP AND LIGHTING FIXTURE Incandescent Mercury Metal Halide High Pressure Sodium Fluorescent

CLEAN 0.74 0.70 0.64 0.77 0.71

AVERAGE 0.69 0.65 0.59 0.71 0.66

Table 7. Suggested Total Light Loss Factor (From Crouse-Hind catalog) e.

Calculate Lamp Lumens Required Formula: PRESENTATION OF LIGHTING CALCULATION

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DIRTY 0.64 0.60 0.55 0.66 0.61

.1

Total Lamp Lumens = Footcandles x Area of room(sq.ft) Coefficient of Utilization x Light Loss Factor

f.

Calculate Number of Lighting Fixtures Required Formula: Lighting Fixtures = Total Lamp Lumens Total Lamp Lumens per lighting Fixture Example Calculation A 60’ x 60’ x 9’ room with task illumination objective of 25 footcandles average at 2.5’ work plane has been specified using 2 x 36 Watt Fluorescent recessed type lighting fixture, 6000 Lumens. RCR = 5 x 6.5’ (60’ + 60’) 60’ x 60’ =

1. 083

FCR = 5 x 2.5’ (60’ + 60’) 60’ x 60’ = 0.41 From the table given by vendor at the catalog, CU = 0.75 (just sample) LLF = 0.66 (From Suggested Total Light Loss Factor above)

Lighting fixtures required = 25 x 3600 ( 0.75 x 0.66 ) x 6000 PRESENTATION OF LIGHTING CALCULATION

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= 30.3 Rounded become 30.

6.2

POINT-BY-POINT METHOD This method use to determine the footcandle value at a point on a surface that is illuminated by direct light from a lighting fixture or more.

ө

d

O

P

Formula: Footcandles = Candlepower x cosine of angle ө --------------------------------------- x Light Loss Factor d 2 (distance)

6.2.1 Example Calculation

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An area with task illumination objective of 2.0 Footcandles at the Floor level has been

specified using 200 Watt Incandescent. Lighting Fixture Lamp mounting height (h) Photometric curve

: 2 00 watt Incandescent : 12’ above grade level : As given below (adopted from Crouse-Hind Catalogue)

LLF

: 0.69

At O point, FC = 715 x 1.0 122

x 0.69 = 3.4 FC

At P point Candlepower at 30 degree d = 13.9’ FC = 779 x 0.866 x 0.69 = 2.4 FC 13.9

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