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16469 Low Energy Building Design Lighting Cameron Johnstone Department of Mechanical Engineering

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Presentation on theme: "16469 Low Energy Building Design Lighting Cameron Johnstone Department of Mechanical Engineering"— Presentation transcript:

1 16469 Low Energy Building Design Lighting Cameron Johnstone Department of Mechanical Engineering

2 16469 Low Energy Building Design: Lighting Three tasks of a lighting system: -Ensure safety environment illuminated enabling hazard identification -Facilitate performance enable tasks to be undertaken in optimum illumination -Create a Visually Comfortable Environment avoid contrast in luminous intensity

3 16469 Low Energy Building Design: Lighting Lighting Sources -Natural (sunlight, direct and diffuse) -Artificial (crude approximation to the above) Natural =>380 nm nm wavelengths Artificial =>consists of a combination of wavelengths within the above spectrum.

4 16469 Low Energy Building Design: Lighting Natural =>380 nm nm wavelengths

5 16469 Low Energy Building Design: Lighting Choosing Lamp Type -Highest efficacy (Best Practice) Lamp Efficacy = / P -where: = luminous flux (lm) P= lamp power - Domestic applications: compact fluorescent - Industrial applications: Low pressure sodium

6 16469 Low Energy Building Design: Lighting - Colour rendering Street lighting: low quality, highest efficacy (Na based) Social: towards red end of the spectrum to create right ambiance (warm) Commercial: towards blue end of the spectrum to create alertness (cool)

7 16469 Low Energy Building Design: Lighting Light is delivered from two source paths: i)Diffuse: e.g. Upward lighting reflected of ceiling ii) Direct: e.g. Downward lighting from a spot lamp Classification of any direct light distribution expressed to the nearest BRITISH ZONAL (BZ) number.

8 16469 Low Energy Building Design: Lighting Design Methods -Most precise part of lighting specification. Need to consider illumination at a point from i)Direct flux ii)Direct plus reflected flux Direct illuminance Illuminance at a point directly below a source can be determined by the INVERSE SQUARE LAW:

9 16469 Low Energy Building Design: Lighting I B C E = I o /H 2 where:Io = Intensity towards point H = Height of light above plane A H I0I0 L

10 16469 Low Energy Building Design: Lighting By introducing an angle between lamp and point of illumination, results in the following: i) measuring distance (H) has increased ii) the intensity has changed from I 0 to I iii) the illuminated plane has increased The resulting illumination is calculated from the COS 3 LAW of ILLUMINATION

11 16469 Low Energy Building Design: Lighting A BL From previous, we can state that: Cos = LA / LB and the illuminance at point B falls by a factor of Cos to become: E = I Cos LB 2 I B C A H I0I0 L

12 16469 Low Energy Building Design: Lighting A BL From the initial diagram, we can deduce that Cos = H / LB LB = H / Cos Substituting for LB in the equation previously, becomes E = I Cos 3 H2H2

13 16469 Low Energy Building Design: Lighting Average Illuminance Source illuminated via light from: -Direct -Defusing surfaces -Reflective surfaces Lumen Method adopted where: E = service illuminance (lx) A = area of working plane (m 2 ) U.F. = Utilisation Factor L.L.F. = Lamp Loss Factor

14 16469 Low Energy Building Design: Lighting Utilisation Factor (UF) Determined from Room Index (Kr) Lamp Loss Factor (LLF) LLF = Lamp lumen MF x Luminaire MF x Room surface MF

15 Floor area Window Low Energy Building Design: Lighting Lighting System Layout 1- Calculate number of lamps required 2- Maintain uniformity in installation 3- Always increase the number of lamps used to achieve 2

16 16469 Low Energy Building Design: Lighting Daylight Reduce:Energy demands Displace artificial lighting requirements Daylight Factor (DF) - % of light received from a sky of known illuminance. DF components:Direct through window Reflected of internal surfaces Window component consists of: i)Sky ii)Externally reflected

17 16469 Low Energy Building Design: Lighting Simplified BRE DF calculation DF > 5Excellent potential 2 < DF < 5Potential with good design DF < 2Limited potential Where: C G = Gazing obstruction coefficient (dirt/ barriers totransmission) A G = Area of glazing = Angle of visible sky = Glazing transmission factor A is = Area of internal surfaces b = area weighted reflectance of room surfaces

18 16469 Low Energy Building Design: Lighting Daylight Penetration Limited penetration =>Illumination contrast => cause of Glare Caused by: Room depth > Limiting depth BRE limiting Depth Asymmetric rooms with windows on opposite sides, limiting depth = 2D Where: w = room width parallel to window h = height of window above floor b = area weighted reflectance in half of roomopposite the window

19 16469 Low Energy Building Design: Lighting Control and wiring: to maximise use of daylight and minimise electricity consumption - Daylight responsive luminaire with integral photocell - Common wiring of luminaires at windows and those deeper in the room - Calibration of daylight sensor to representative illuminance at the point of installation Floor area Window


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