16469 Low Energy Building Design Lighting

1. 16469Low Energy Building Design Lighting Cameron Johnstone Department of Mechanical Engineering cameron@esru.strath.ac.uk

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 - 760 nm wavelengths Artificial => consists of a combination of wavelengths within the above spectrum.

4. 16469 Low Energy Building Design: Lighting Natural => 380 nm - 760 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: • Diffuse: e.g. Upward lighting reflected of ceiling • 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. L  C I0 H I A B 16469 Low Energy Building Design: Lighting E = Io/H2 where: Io = Intensity towards point H = Height of light above plane

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 I0 to I iii) the illuminated plane has increased The resulting illumination is calculated from the COS3 LAW of ILLUMINATION

11. L  A C   I0 L B H I A B 16469 Low Energy Building Design: Lighting 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  LB2

12. A   L B 16469 Low Energy Building Design: Lighting From the initial diagram, we can deduce that Cos  = H / LB LB = H / Cos  Substituting for LB in the equation previously, becomes E = ICos3  H2

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 (m2) 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 lumenMF x LuminaireMF x Room surfaceMF

15. Floor area Window 16469 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 Where: CG = Gazing obstruction coefficient (dirt/ barriers to transmission) AG = Area of glazing  = Angle of visible sky  = Glazing transmission factor Ais = Area of internal surfaces b = area weighted reflectance of room surfaces Simplified BREDF calculation DF > 5 Excellent potential 2 < DF < 5 Potential with good design DF < 2 Limited potential

18. Where: w = room width parallel to window h = height of window above floor b = area weighted reflectance in half of room opposite the window 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

19. Floor area Window 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