Lighting Design Terminology Quiz

Definition of Terms

• Illumination: The intensity of light per unit area.
• Electric Illumination: Light production using electricity, aiming for efficient, comfortable, and safe vision.
• Lighting Design: The art and science of creating lighting schemes.
• Quantity of Light: The amount of illumination (luminous flux) per unit area.
• Quality of Light: The distribution of brightness in a lighting installation.
• Brightness: The light perceived from an object.
• Contrast: The difference in brightness between an object and its background.
• Glare: Strong, steady, dazzling light or reflection.
• Diffuseness: Control of shadows cast by light.

Estimating Illumination and Brightness

• Illuminance Meters: Devices measuring illumination levels.

  • Comparator Type: Requires subjective judgment of brightness equivalence.
  • Direct Reading Type: Uses a hooded cell to measure illumination directly.
  • Accurate Laboratory Instruments: Unsuitable for fieldwork.

• Units of Illumination:

  • Footcandle (fc): Light flux density, measured in lumens per square foot. Used to describe the amount of light in a room.
  • Footlambert (fl): Luminance of a surface, measured in lumens per square foot of area viewed.

Illustration 1

• A 40-watt fluorescent lamp (120 cm long) produces 3,200 lumens in a 10 ft. x 20 ft. room.
• To determine the illumination on the floor:
  • Calculate the area of the room (200 square feet).
  • Divide the total lumens (3,200) by the area (200 sq. ft.) to get the illumination (16 footcandles).

Points to Remember

• Rule of Thumb Illumination Levels:
  • 10 footcandles for halls and corridors.
  • 30 footcandles for spaces between workstations (e.g., office areas except desks).
  • 50 footcandles for office work areas with desks.

Illustration 2

• To calculate luminance, using the reflectance factor of the wall:
  • Footlambert = Footcandle x Reflectance factor
  • Example: 16 footcandles x 40% = 6.4 footlamberts

Lighting units in Metric Measures

• Lumens : remains the same unit for luminous flux.
• Lux: The unit used for illumination or light flux density in the metric system.

Table 1: Approximate Reflectance Factor

• This table provides approximate reflectance factors for various surfaces commonly found in buildings. Understanding these factors is crucial for accurate lighting calculations.

Table 2: Table of Comparison

• This table compares various units of measurement used for illumination and brightness.

• Millilambert: A practical unit of luminance because lamberts are typically large values.

Illustration 3

• Calculation of Illumination (English and Metric)
  • English: using footcandles.
  • Metric: using lux.

Another Solution

• Provides a different method for calculating illumination using the same example as Illustration 3.

Illustration 4

• Calculation of Brightness of a Fixture:
  • Given a 1' x 4' plastic diffuser with transmittance of 0.6 illuminated by two 3,200 lumen lamps.
  • Using the formula: Brightness = (Total lumens x Transmittance) / Area

Coefficient of Utilization and Maintenance Factor

• Coefficient of Utilization (CU): Represents the efficiency of a luminaire in transferring light to a working plane in a specific area.
• Maintenance Factor (MF): Accounts for the depreciation of lamps and reflective surfaces over time, affecting illumination levels.
• Usable Initial Footcandle: The footcandle produced by the coefficient of utilization (CU).

Table 3: Coefficient of Utilization

• This table provides CU values for different types of luminaires and room configurations, essential for lighting calculations.

Illustration 5

• Calculating Initial and Maintained Illumination:
  • Example: A classroom illuminated with 10 fluorescent lamps, given CU and MF values to calculate initial and maintained footcandles (English) and lux (Metric).

Conclusion

• Understanding the definitions, units, and calculation methods for illumination is important for effective lighting design in various settings.
• Using the provided tables, illustrations, and formulas, you can determine appropriate illumination levels and design lighting systems that meet specific requirements for comfort, safety, and visual performance.