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16469 Low Energy Building Design Lighting. Cameron Johnstone Department of Mechanical Engineering cameron@esru.strath.ac.uk. 16469 Low Energy Building Design: Lighting. Three tasks of a lighting system:   - Ensure safety environment illuminated enabling hazard identification

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16469 low energy building design lighting
16469Low Energy Building Design Lighting

Cameron Johnstone

Department of Mechanical Engineering

cameron@esru.strath.ac.uk

16469 low energy building design lighting2
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

16469 low energy building design lighting3
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.

16469 low energy building design lighting4
16469 Low Energy Building Design: Lighting

Natural => 380 nm - 760 nm wavelengths

16469 low energy building design lighting5
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
16469 low energy building design lighting6
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)

16469 low energy building design lighting7
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.
16469 low energy building design lighting8
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:
16469 low energy building design lighting9

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

16469 low energy building design lighting10
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

16469 low energy building design lighting11

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

16469 low energy building design lighting12

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

16469 low energy building design lighting13
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

16469 low energy building design lighting14
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

16469 low energy building design lighting15

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

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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

16469 low energy building design lighting17
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

16469 low energy building design lighting18

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

16469 low energy building design lighting19

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