Calculations of illumination


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Calculations of illumination

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Calculations of illumination

  1. 1. Chapter 16 Calculations of Illumination
  2. 2. Quantity and Quality of Illumination In lighting design, several tentative selections and equipment layouts may have to be made prior to achieving an optimum solution. Experienced designers can often shorten this process. Quantity and quality of illumination are inseparable. High-quality lighting compensates for a lack of quantity. Poor lighting requires higher lighting quantity.
  3. 3. Basis for Illumination Illumination calculations are based on the principle of luminous flux transfer from the light source or sources to a surface. Normally, the transfer is through clean air and is assumed to have no loss. Calculating Illuminance: (Chapter 14) Lumen Method: E = F / A Point Method: E = I / d2 These definitions MUST be modified when applying in actual lighting design.
  4. 4. Basis for Illumination Why? Not all luminous flux coming from the light source can be aimed totally on the surface. Light flux of lamps will depreciate with age How? By including several correction factors or coefficients Applicability of the two methods: Lumen Method: only practical method to use manually if the light source is large or is diffused Point Method: almost exclusively for sports lighting design, especially for outdoor athletic fields.
  5. 5. The Zonal Cavity Method Application of the lumen method to determine the horizontal illuminance on a working plane in an interior space. Introduces two simple modification factors: Coefficient of Utilization (CU): percentage of total lamp lumens that can be utilized in the room based on the room size, configuration, surface reflectance and performance characteristics of fixtures. Light loss factor (LLF): accounts for light losses due to depreciation. E = (F/A) x CU x LLF
  6. 6. The Zonal Cavity Method Light loss factor (LLF): represents the components of light loss of a lighting system initially as well as during normal operations. These components may be divided into two groups, with each group containing several factors: Group 1: Nonrecoverable light loss factors: inherent in the installed system and cannot be corrected through routine maintenance. Voltage Factor Temperature Factor Tilt Factor Ballast Factor Fixture surface depreciation factor
  7. 7. The Zonal Cavity Method Light loss factor (LLF): Group 2: Recoverable light loss factors: can be changed by regular maintenance, such as cleaning relamping, and painting of room surfaces. Lamp lumen depreciation factor Fixture dirt depreciation factor Room surface depreciation factor Lamp burnout factor
  8. 8. Point Method Initial Illuminance: (Chp 14) Eih=(I/d2 ) x cos Θ Eih =I x (cos3 Θ) / h2 Eiv=(I/d2 ) x sin Θ Eiv =I x (cos2 Θ) x (sin Θ) / h2 Maintained Illuminance: Emh = Eih x LLF Emv = Eiv x LLF