Lighting Design Terminology Quiz

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Questions and Answers

What is the relationship between Footlambert and Footcandle?

Footlambert equals Footcandle divided by Reflectance factor.

Footlambert equals Footcandle multiplied by Reflectance factor. (correct)

Footlambert equals Footcandle plus Reflectance factor.

Footlambert equals Footcandle minus Reflectance factor.

Which unit is used to express illumination or light flux in metric measures?

Lux (correct)

Luminance

Lumens

Footcandle

What does the Coefficient of Utilization (cu) measure?

The efficiency of a luminaire in transferring luminous energy. (correct)

The amount of lumens produced per watt of energy used.

The ratio of maintained illumination to initial illumination.

The total amount of light produced by a lamp.

What does the Maintenance Factor (mf) account for in lighting calculations?

Depreciation of lamps and reflective surfaces. Signup and view all the answers

How do you compute the initial footcandle in a lighting scenario?

Lumens times Coefficient of Utilization times Maintenance Factor divided by Area. Signup and view all the answers

What is the approximate reflectance factor given in the provided content?

40% Signup and view all the answers

What is the formula for converting 10 ft. x 20 ft. to metric dimensions in meters?

7.32 m x 9.14 m Signup and view all the answers

Why is millilambert preferred over lambert in certain situations?

It is a smaller unit and more commonly encountered. Signup and view all the answers

What is the unit of measure used to describe the amount of light in a room?

Footcandle Signup and view all the answers

Which term refers to the distribution of brightness in a lighting installation?

Quality of Light Signup and view all the answers

What does the term 'contrast' signify in lighting design?

The brightness ratio between an object and its background Signup and view all the answers

What is the recommended illumination level in footcandles for office work areas?

50 Signup and view all the answers

Which type of illuminance meter requires the operator to make a brightness equivalence judgment?

Comparator Type Signup and view all the answers

What does 'diffuseness' refer to in lighting principles?

Control of shadows cast by light Signup and view all the answers

Which of the following is NOT a factor that affects illumination?

Color Temperature Signup and view all the answers

When calculating illumination on the floor from a 40-watt fluorescent lamp, what is the total lumen output?

3200 lumens Signup and view all the answers

Study Notes

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.

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Description

Test your knowledge on key terms related to lighting design and illumination. This quiz covers definitions, concepts, and techniques essential for understanding lighting dynamics. Perfect for students and professionals in the field of design and architecture.