Study Notes on Electrical Building Services: Lighting

Electrical Building Services for Residential Buildings

Overview of Lecture

• Lecturer: Susan

• Focus: Electrical lighting within power systems for residential buildings.

• Course Outcome Alignment: The lecture relates to describing various services including energy and power.

Building Code Reference

• Clause G7:

  • Requirement: Safeguard occupants from illness or loss of amenity due to isolation from natural light.

  • Mandates presence of windows in buildings.

• Clause G8:

  • Objective: Prevent injury due to inadequate lighting.

  • Specifies minimum light requirements for inhabited spaces.

  • Necessitates a minimum of 30 lux for natural light and 20 lux for artificial lighting on the floor.

Understanding Light

• Types of Light Waves:

  • Microwaves, x-rays, radio waves are invisible forms of the electromagnetic spectrum.

• Visible Light:

  • Only portion visible to the human eye; encompasses wavelengths from violet ($ ext{approximately } 380 ext{ nm}$) to red ($ ext{approximately } 780 ext{ nm}$).

• Ultraviolet Light:

  • Wavelengths below violet, invisible.

• Infrared Radiation:

  • Wavelengths above red, invisible.

Spectral Power Distribution

• Graph Representation:

  • Each light source has a unique spectral power distribution curve.

  • Example: LED light source shows peaks in blue and yellow regions, producing white light by combining various colors.

• Response of Human Eyes:

  • Eyes respond differently to different wavelengths and light levels; peak sensitivity of human vision at $ ext{555 nm}$ (yellow-green region).

Units of Measurement in Lighting

• Luminous Flux:

  • Definition: Measures the total light output of a source.

  • Symbol: Greek letter phi (Φ).

  • Unit: Measured in lumens (lm).

  • Example: A bulb may emit 500 lumens.

• Luminous Efficacy:

  • Definition: Measures the efficiency of a light source based on lumens produced per watt of electricity consumed.

  • High efficacy examples: LEDs with $ ext{over } 100 ext{ lm/W}$.

  • Calculation Example: For $ ext{500 lm}$ output at $ ext{5.5 W}$, efficacy = $ rac{500 ext{ lm}}{5.5 ext{ W}} ext{ approximately } 91 ext{ lm/W}$.

• Illuminance:

  • Definition: The amount of luminous flux arriving on a surface, indicating how well an area is illuminated.

  • Unit: Measured in lux (lx).

  • Illuminance Calculation:

  • Given by the formula: ext{Illuminance} = rac{ ext{Intensity}}{ ext{Distance}^2}.

  • Real-world application: If 1 lux is at 1 meter, then at 2 meters it is $ rac{1}{2^2} = rac{1}{4}$ lux.

  • Building Code Requirements:

  • 30 lux on the floor for 75% of the standard year from natural light (Clause G7).

  • Minimum of 20 lux for artificial lighting (Clause G8).

Illuminance Requirements for Spaces

• Residential Spaces:

  • Generally no strict illuminance requirements unless specified (e.g., G7 and G8).

• Commercial Spaces:

  • Stricter specifications: example, at least 320 lux in office spaces.

• Impact of Room Colors:

  • Dark colors absorb more light and require additional lighting; reflective percentages:

  • Quarter Pavlova reflects 70% light,

  • Pavlova reflects 51%,

  • Triple Pavlova reflects 35%.

Color in Lighting

• Correlated Color Temperature (CCT):

  • Definition: Measures the color appearance of a light source, presented in Kelvin (K).

  • Low values (e.g., 2700K): indicate warm, yellowish light.

  • High values (e.g., 6500K): indicate cool, bluish light.

  • Example: Typical household bulbs often rated at 2700K for a warm environment.

• Circadian Rhythm:

  • Function of light: affects sleep cycles influenced by light colors and intensity, with blue light being impactful at night.

Color Rendering in Lighting

• Color Rendering Index (CRI):

  • Definition: Measures the ability of a light source to reveal the colors of various objects accurately.

  • Scale: Ranges up to a maximum of 100 (not percentage); higher values indicate better performance.

  • Impact of Lighting on Perception:

  • Different light colors can obscure the true appearance of objects depending on the lighting conditions.

Types of Light Sources

• Incandescent Lamps:

  • Functioning: Light produced by heating a filament inside a glass envelope.

  • Color Temp: Commonly around 2700K to 2800K.

  • Efficiency: Generally low, primarily produces heat rather than light; not commonly used in homes today except for accent lighting.

• Halogen Lighting:

  • A type of incandescent lighting with improved efficiency; varies in voltage (e.g., GU10 for 230V, MR16 for 12V).

• Fluorescent Lamps:

  • Gas discharge lamps utilizing low-pressure gas and phosphor coating to convert UV radiation to visible light.

  • Usage: Often found in garages and workshops.

• Compact Fluorescent Lamps (CFL):

  • Similar technology to fluorescent lamps but with a compact form for various applications.

  • Spectrum characterized by multiple peaks based on gas and coatings.

• LEDs (Light Emitting Diodes):

  • Produce light via electronic processes; phosphor coating used to create white light from blue outputs.

  • Compact form factor allows integration into fixtures; once dead, entire unit requires replacement due to integration.

Additional Considerations in Lighting

• Durability and IP Rating:

  • IP (Ingress Protection) rating defines the resistance to dust and moisture. Example: An IP65 rating indicates total dust ingress protection and water resistance from jets.

• Heat Dissipation:

  • Heat management is crucial; overheating can diminish light output and lifespan, necessitating heat sinks for devices like LEDs.

• Safety Concerns:

  • Highlighting risks, such as potential fire hazards when lighting interacts improperly with materials (e.g., curtains).

Conclusion

• This lecture encompassed crucial aspects of electrical building services with a focus on lighting, touching upon lighting types, design considerations, unit measurements, and the relationship of lighting to health and safety within residential environments.