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Lighting calculations

Lighting calculations. The Illuminance: (E) شدة الإضاءة = Luminous Flux / area of the sphere surface E= Φ/ A E= I/ r 2 = lumen/ m 2 = lux. The luminance (Luminous Intensity) (I) شدة الاستضاءة I= Φ/ω cd Where: ω = solid angle = (Φ/A)* r 2 = E* r 2 Candela.

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Lighting calculations

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  1. Lighting calculations

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

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

  4. 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 luxto ¼ lux

  5. 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)

  6. 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 (∞) Ep= I /h2 cos3 ∞

  7. 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 reflectancesof the above three surfaces affect the quantity of reflected light received by the working plane.

  8. Factors affected on illuminance calcuations • Room surface maintenance factor(RSMF) is the proportionofthe 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 • 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.

  9. Lumen Method Calculations

  10. 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

  11. The Luminous Flux (Φ)= EA/MU

  12. 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

  13. Room Factor 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

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