Sample

Sample Illumination Calculation

Outdoor Calculation

(Illuminance at a Point-Direct Component)

Inverse Square Law

P A

w

Light Source

Solid Angle

Plane

D

i

s

t

a

n

c

e

d

E = I/ d2

I

Inverse Square Law

E = I/ d2

Where:

E = Illuminance on the surface

I = Luminous intensity of the source in the direction

of the surface

d = Distance from the source to the surface

Example: A point light source has an intensity of 1,000 candela and the light falls perpendicularly on a surface. Calculate the illuminance on the surface if its distance from the surface is: (i) two metres, (ii) four metres and (iii) six metres.

Cosine Law

P

Light Source

Plane

Distance, d

I E = I / d2 cos

Example: A point light source has an intensity of 2,000 candela in all directions and is mounted 4 metres above a surface. Calculate the illuminance on the surface directly underneath (Ea) and at a distance of 3 metres to the side (Eb).

Sample Illumination Calculation

Average Illuminance

1.

As per assignment

37 2 lamp diffuse wraparound General diffuse 2 lamps

Perimeter: Area:

2.

Figure 9-5 Figure 9-4 (5 degrees of dirt conditions) 12 hrs/day 12 months

3.

0.0 m 3.5 m 1.0 m

4.

0 6.135 2.454

4.

Effective Ceiling Cavity Reflectance Computation Refer to Figure 9-11. Since CCR = 0, ρcc = 80%

Effective room surface reflectance

NOTE: STATE ACTUAL REFLECTANCES OF THE ROOM

80% 18%

4.

Effective Floor Cavity Reflectance Computation From Figure 9-11, @ ρf = 20%, ρw = 50%, FCR = 2.454

Effective room surface reflectance

NOTE: STATE ACTUAL REFLECTANCES OF THE ROOM

FCR ρcc

2.4 18

2.454 X1

2.6 18

X1 = 18.0 = ρfc

80% 18%

4.

Initial Coefficient of Utilization (CU1) From Figure 9-12, @ ρcc = 80%, ρw = 50%, CN = 37 RCR = 6.135

X1 = 22.73 = CU initial

RCR CU1

6 23

6.135 X1

7 21

4.

Multiplying Factor (MF) From Figure 9-13, @ ρfc = 10%, ρcc = 80%, ρw = 50%, CN = 37 RCR = 6.135

X = MF @ ρfc = 0.10 = 0.9695

RCR ρfc

6 0.969

6.135 X1

7 0.973

4.

Multiplying Factor (MF) From the obtained value, @ ρfc = 18

X = MF = 0.9939

ρfc MF

20 1

18 X

10 0.9695

4.

CU = CU1 X MF CU = 22.73 x 0.9939

CU = 22.5913

5.

Lamp Lumen Depreciation Computation From Table IV (LLD), @ 12 hours per start and rapid start 430ma standard colors, LLD = 0.866

0.86 0.90 0.88 0.6494

Lamp Burnout Factor Computation Assumed to be 0.90

Light Loss Factor

Room Surface Dirt Depreciation Computation From Figure 9-7, given an area atmosphere of very clean and a cleaning cycle of 12 months, % expected dirt depreciation = 12%.

Luminaire Dirt Depreciation Computation From figure 9-5 (Category II), given an area atmosphere of very clean and a cleaning cycle of 12 months, LDD = 0.97

Light Loss Factor Computation LLF = LLD*LBO*LDD*RSDD

RSDD Factors

6. total initial lamp lumens (TILL)

7. Select practical lay-out for the luminaire.

8. Determine luminaire spacing based on the luminaire orientation chosen.

9. Draw plan of the room and indicate the locations of luminaires.

10. Compute for the actual minimum maintained lighting level.

Eactual = 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 (𝑎𝑓𝑡𝑒𝑟 𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒 𝑠𝑝𝑎𝑐𝑖𝑛𝑔 𝑐𝑜𝑛𝑠𝑖𝑑𝑒𝑟𝑎𝑡𝑖𝑜𝑛)

𝑙𝑢𝑚𝑖𝑛𝑎𝑖𝑟𝑒𝑠 (𝑒𝑞𝑢𝑎𝑡𝑖𝑜𝑛 𝑏𝑎𝑠𝑒𝑑)

Reference:

Philippine Efficient Lighting Market Transformation Project (PELMATP). Lighting Calculations.

Kelly, Kevin and O’ Connell, Kevin. Interior Design Lighting: A Student’s Guide.