EET-314 Lighting Design and Technology Week 2 PDF

EET-314 LIGHTING DESIGN AND TECHNOLOGY Week # 2 School of Engineering Technology & Applied Science (SETAS) LIGHTING METRICS AND CALCULATIONS Objectives Learn the different photometric measurements a...

EET-314 LIGHTING DESIGN AND TECHNOLOGY Week # 2 School of Engineering Technology & Applied Science (SETAS) LIGHTING METRICS AND CALCULATIONS Objectives Learn the different photometric measurements and units Perform basic lighting design calculations using standard lighting units. SETAS - AMAT: EET-314 Week #2 2 Lighting Metrics: Light Measurements Standard units in physical science do not take into consider human sensitivity to light radiation Watts, standard scientific unit for power does not accurately describe light output (e.g. A 100W tubular fluorescent lamp gives almost seven times as much light as an ordinary 100W filament lamp! Special set of measurements and units have been adopted for specifically for lighting Human eye is more sensitive to certain wavelengths of visible light SETAS - AMAT: EET-314 Week #2 3 Lighting Metrics: Spectral Eye Sensitivity Spectral luminous efficiency or spectral eye sensitivity (Vλ ) is the method used to measure power (emitted in Watts) over a series of narrow wavebands. This luminosity curve gives the relative eye sensitivity (Vλ) as a function of wavelength Scotopic Photopic Vision Vision Spectral luminous efficiency (Vλ ) is used to determine the output of a lamp in lumens SETAS - AMAT: EET-314 Week #2 4  Lighting Metrics: Luminous Flux Quantity Unit Abbreviation Luminous Flux (Φ) lumen lm Output of a lamp is measured in lumens and the quantity is Luminous Flux Luminous Flux is proportional to the power emitted by the light source times the Spectral luminous efficiency SETAS - AMAT: EET-314 Week #2 5  Lighting Metrics: Luminous Efficacy Quantity Unit Abbreviation Luminous efficacy (η) Lumen per watt lm/W Luminous efficacy is the ratio of luminous flux to power consumption (lm/W) Used to measure the energy efficiency of a lamp Efficacies vary with type and size of lamps  A typical incandescent lamp may be around 10 lm/W,  A modern T8 lamp with electronic ballast has about 100 lumens per watt http://www.build.com.au/luminous-efficacy SETAS - AMAT: EET-314 Week #2 6 Lighting Metrics: Luminous Efficacy To calculate the efficacy for a lamp that requires a ballast, you must add the ballast power to the lamp power to get the correct total wattage input. The higher the lumen per watt rating of a lamp the better -- meaning greater light output for a fixed wattage input. http://www.build.com.au/luminous-efficacy SETAS - AMAT: EET-314 Week #2 7 Lighting Metrics: Luminous Efficacy Examples 1. A 60 watt incandescent lamp has an output of 1100 lumens. What is the efficacy? 2. A fluorescent fixture contains two 40 watt lamps and a ballast that draws 20 watts. If each lamp produces 3000 lumens, what is the efficacy of the lamps and the fixture? SETAS - AMAT: EET-314 Week #2 8  Lighting Metrics: Solid Angle A solid angle is the three-dimensional A 1-steradian solid angle removed from a equivalent to a two-dimensional angle sphere. A solid angle is measured in steradians, the three-dimensional equivalent of radians the solid angle subtended at the centre of a sphere by an area on its surface numerically equal to the square of the radius A solid angle that measures 1 steradian, A = r2. A  r2 Ex: a one-steradian section of a sphere that has a 1-meter radius subtends a surface area of one square meter. 9  Lighting Metrics: Luminous Intensity Quantity Unit Abbreviation Luminous Intensity (I) candela cd Luminous intensity is the quantity of light emitted per second in a specific direction I is defined as the luminous flux (Φ )in a specified direction, radiated per unit of solid angle ω Luminous intensity information for luminaires can be obtained  I from manufacturers candela curve/chart  Center Beam Candle Power, CBCP = intensity at 0⁰ Beam Angle = 50% of max CBCP Φ Field Angle = 10% of max CBCP Phillips: Theory of Light and Lighting http://www.pveducation.org/pvcdrom/properties-of-sunlight/properties-of-light SETAS - AMAT: EET-314 Week #2 10 Lighting Metrics: Luminous Intensity SETAS - AMAT: EET-314 Week #2 11  Lighting Metrics: Illuminance Quantity Unit Abbreviation Illuminance (E) lux lx (lm/m2) (lumens per sq. meter) fc (lm/ft2) footcandle (lumens per sq. ft.) Illuminance is the amount of light or luminous flux falling on a surface area  E A light meter NOTE: 1 fc ≈ 10 lx Phillips: Theory of Light and Lighting http://www.pveducation.org/pvcdrom/properties-of-sunlight/properties-of-light SETAS - AMAT: EET-314 Week #2 12  Lighting Metrics: Luminance Quantity Unit Abbreviation candelas per sq. meter Luminance (L) cd/m2 candelas per sq. ft cd/ft2 Luminance (L) is the luminous intensity (I) emitted per unit area (A) traveling in a given direction. Related to the physical sensation of brightness Can be light emitted from lamp or reflected from surface I L A Phillips: Theory of Light and Lighting luminance meter http://www.pveducation.org/pvcdrom/properties-of-sunlight/properties-of-light SETAS - AMAT: EET-314 Week #2 13 Lighting Calculations: Inverse-Square Law (for Illuminance) The inverse square law relates the quantities of illuminance and luminous intensity with the radius of a projected light source We know: φ φ Inner surface of a sphere E  being illuminated by a A ωr 2 small light source Since:  I   Therefore: I E r2 © 2014 Robert Bean. Courtesy Routledge Publishing SETAS - AMAT: EET-314 Week #2 14  Lighting Calculations: Inverse-Square Law We can rearrange the equation such that the radius (r) of the surface of the sphere is the distance (d) between the light and the illuminated point I E d2 Example 3: If luminous intensity if a light source is 100 cd, calculate illumance for: 1 m, 2 m and 3 m Phillips: Theory of Light and Lighting http://www.pveducation.org/pvcdrom/properties-of-sunlight/properties-of-light SETAS - AMAT: EET-314 Week #2 15  Lighting Calculations: Point Method, Perpendicular If the light source is perpendicular to the surface, the inverse square law can be used to calculate E directly I E d2 Example 4: d If a lamp with a CBCP of 6000 cd is pointed towards a table below, how many fc would hit the surface 10 ft directly below? SETAS - AMAT: EET-314 Week #2 16 Lighting Calculations: Pont Method, Horizontal Illuminance (Cosine Law) Practical calculations require more than the inverse-square law relationship The angle (θ) that the direction of light incidence makes with the normal must be taken into account when the light incidence of the light source is not perpendicular to the point (P2) I cos  E d2 h © 2014 Robert Bean. Courtesy Routledge Publishing SETAS - AMAT: EET-314 Week #2 17 Lighting Calculations: Pont Method, Horizontal Illuminance (Cosine Law) Example 5: A light source provides a luminous intensity of 36,000 cd at an angle of 40⁰. Calculate the horizontal illuminance (in foot candles) at a point, 20 feet distance from the source. SETAS - AMAT: EET-314 Week #2 18 Lighting Calculations: Pont Method, Vertical Illuminance If light is directed towards a vertical display, we will need to calculate vertical illuminance. This can be calculated using the following formula: I sin  E d2 θ Example 6: What is the vertical illumance if a candlepower of 6000 cd is pointed at 30⁰ towards a vertical surface 10 ft away? Note: You can still apply the cosine law if you modify the viewers reference point SETAS - AMAT: EET-314 Week #2 19 Lighting Calculations: Point Method Example 7: a) Calculate the illuminance at a point on a church tower clock which is 8m above the ground. The floodlight is sited directly beneath the clock and 4m from the base of the tower. It is aimed so that its peak intensity of 10,733 cd is directed at the clock © 2014 Robert Bean. Courtesy Routledge Publishing SETAS - AMAT: EET-314 Week #2 20 Lighting Calculations: Point Method b) Repeat calculation assuming floodlight must be displaced 3m parallel to the front of the tower to be opposite the right-hand side of the tower, as shown below © 2014 Robert Bean. Courtesy Routledge Publishing SETAS - AMAT: EET-314 Week #2 21 Lighting Calculations: Cylindrical Illuminance (Mean Vertical Illuminance) The average cylindrical illuminance over an infinitely small cylinder can be expressed as: I Ecyl  sin  cos 2  h 2 Another form of the equation relating angle to distance is: I sin  Ecyl  d 2 This angle is also equal to θ (alternate angles) Referring to figure, sinθ=N/d, Therefore: Note: This is not IN  3 the symbol for flux, Ecyl d this is for angle © 2014 Robert Bean. Courtesy Routledge Publishing SETAS - AMAT: EET-314 Week #2 22  Lighting Calculations: Cylindrical Illuminance (Mean Vertical Illuminance) The concept of cylindrical illuminance is used to check if objects in a room such as people and wall get enough light. Optimal lighting for facial features requires a ratio of cylindrical illuminance to horizontal illuminance between 0.3 and 0.6 https://glamox.com/uk/en-12464 SETAS - AMAT: EET-314 Week #2 23 Lighting Calculations: Cylindrical Illuminance (Mean Vertical Illuminance) SETAS - AMAT: EET-314 Week #2 24 Lighting Calculations: Cylindrical Illuminance (Mean Vertical Illuminance) Example 8: Calculate the value of cylindrical illuminance in Figure below given that I = 700 cd, H = 2, N = 2. Also calculate the ratio of cylindrical to horizontal illuminance at the same point. SETAS - AMAT: EET-314 Week #2 25  Summary 1. Spectral luminous efficiency or spectral eye sensitivity (Vλ ) is the method used to measure power (emitted in Watts) over a series of narrow wavebands 2. Luminous flux is a measure of the total quantity of visible light emitted by a source. 3. Luminous Efficacy is the ratio of luminous flux to power consumption (lm/W) 4. A solid angle is the three-dimensional equivalent to a two-dimensional angle 5. Luminous intensity is the quantity of light emitted per second in a specific direction SETAS - AMAT: EET-314 Week #2 26  Summary 6. Spectral luminous efficiency or spectral eye sensitivity (Vλ ) is the method used to measure power (emitted in Watts) over a series of narrow wavebands 7. Illuminance is the amount of light or luminous flux falling on a surface area 8. Luminance is the luminous intensity emitted per unit area traveling in a given direction 9. Inverse Square Law - illuminance on a surface is inversely proportional to the distance-squared of the light source SETAS - AMAT: EET-314 Week #2 27  Summary 10. Cosine Law takes into account the angle of incidence of the light rays striking the surface when measuring illuminance 11. Cylindrical Illuminance - calculate illuminance over an infinitely small cylinder to check if objects in a room such as people and wall get enough light. SETAS - AMAT: EET-314 Week #2 28 Summary SI Photometric Quantities SETAS - AMAT: EET-314 Week #2 29