Lighting calculations

=Luminous Flux / area of the sphere surface The Illuminance: (E) شدة الإضاءة =Luminous Flux / area of the sphere surface E=Φ/A E= I/ r2 = lumen/ m2 = lux

The luminance (Luminous Intensity) (I)شدة الاستضاءة I= Φ/ω cd Where: ω = solid angle = (Φ/A)* r2 = E* r2 Candela

Inverse square law Inverse square law: Double the Radius: Surface area bounded by a solid angle of 1 sr now increases to 4m2 Luminous flux remains Φ = 1lm Illuminance E drops from 1 lux to ¼ lux

What can we do with this? It’s the basic building lighting We can find the illuminance on a desk from a incandescent light bulb overhead: Bulb: 60W * 20 lm/W = 1200 lm 1200/4π ≈ 100 cd if point source Desk : E = 100/22 = 25 lux LUMINOUS EFFICACY Is the ratio of the luminous flux emitted by a lamp to the power taken by it. (unit: LUMENS PER WATT, lm/W)

Calculation of point illuminance level: Ep Which are generated by individual light source: E = I/r2 But, r = h/ cos (∞) So, Where, Luminous Intensity(I) Hieght (h) Light Incidence Angle (∞) E p = I /h2 cos3 ∞

Factors affected on illuminance calculations Room Reflectance The room is considered to consist of three main surfaces: (a) the ceiling cavity, (b) the walls, and (c) the floor cavity (or the horizontal working plane). The effective reflectances of the above three surfaces affect the quantity of reflected light received by the working plane.

Factors affected on illuminance calcuations Luminaire maintenance factor (LMF) is the proportion of the initial light output from a luminaire after a set time to the initial light output from a lamp after a set time. Three factors must be considered in its determination: (a) the type of luminaire, (b) atmospheric conditions, and (c) maintenance interval. Room surface maintenance factor (RSMF) is the proportion of the illuminance provided by a lighting installation in a room after a set time compared with that occurred when the room was clean. Utilization factor (UF) is the proportion of the luminous flux emitted by the lamps which reaches the working plane. Factors that affect the value of UF are as follows: (a) light output ratio of luminaire (b) flux distribution of luminaire (c) room proportions (d) room reflectance (e) spacing/mounting height ratio

Lumen Method Calculations  

i.e. initial bare lamp luminous flux Where: E = average illuminance over the horizontal working plane     n = number of lamps in each luminaire     N = number of luminaire     F = lighting design lumens per lamp, i.e. initial bare lamp luminous flux      UF = utilisation factor for the horizontal working plane      LLF = light loss factor      A = area of the horizontal working plane  

The Luminous Flux (Φ)= EA/MU

The Luminous Flux (Φ)= EA Calculate the utilization factor Calculate the Room Factor: K = 0.8W + 0.2L he Where: W= width of the room L = length of the room From the table find “η” The Luminous Flux (Φ)= EA η

Room Factor It depends on room dimension is the proportion of the initial light output from a luminaire after a set time to the initial light output from a lamp after a set time. It depends on room dimension