Lighting Design in Offices and Education

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Questions and Answers

What is the recommended range for the height of the working plane in offices?

  • 0.90m to 1.00m
  • 0.60m to 0.70m
  • 1.05m to 1.15m
  • 0.75m to 0.85m (correct)

What should the ratio of the minimum to average illuminance for general lighting be?

  • 0.8 (correct)
  • 0.7
  • 1.0
  • 0.5

What is the minimum illuminance level for non-working areas relative to working areas?

  • 90% of working areas
  • 70% of working areas
  • 30% of working areas
  • 50% of working areas (correct)

Why is it important to allow individual control over lighting in office environments?

<p>To accommodate varying visual requirements (B)</p> Signup and view all the answers

What can excessively large differences in luminance cause in an office setting?

<p>Visual adaptation problems (C)</p> Signup and view all the answers

What is the recommended minimum illuminance for an office working area?

<p>350 lux (C)</p> Signup and view all the answers

If the average illuminance between two adjacent areas has a ratio greater than 5:1, what is most likely to happen?

<p>Dark areas will become more noticeable (D)</p> Signup and view all the answers

What type of color appearance is preferred at higher lighting levels?

<p>Cool (bluish white) (A)</p> Signup and view all the answers

Which color rendering index (Ra) is recommended for offices?

<p>At least 80 (B)</p> Signup and view all the answers

In cooler climates, what type of color temperature is generally preferred?

<p>Warm (reddish white) (A)</p> Signup and view all the answers

What is a key consideration in minimizing reflections on VDU screens?

<p>Positioning of VDU workstations and light sources (D)</p> Signup and view all the answers

What lighting system is suggested to eliminate bright spots on VDU screens?

<p>Good indirect lighting (A)</p> Signup and view all the answers

Which of the following statements about color temperature is true?

<p>Higher color temperatures are preferred in warmer climates. (D)</p> Signup and view all the answers

What is the effect of reflections from light sources on VDU screens?

<p>They can deteriorate character legibility. (A)</p> Signup and view all the answers

Which lighting approach is effective for creating an even brightness in a room?

<p>Indirect lighting with uplighters (D)</p> Signup and view all the answers

Which color temperature range is classified as intermediate?

<p>3300 - 5300 K (C)</p> Signup and view all the answers

What is a potential consequence of mixing light sources with different color appearances?

<p>Deterioration in color consistency (A)</p> Signup and view all the answers

What is a disadvantage of indirect lighting?

<p>It can cause the luminaires and ceiling to become dirty sooner. (D)</p> Signup and view all the answers

How does direct lighting compare to indirect lighting in terms of cleanliness?

<p>Direct lighting does not get dirty as quickly as indirect lighting. (A)</p> Signup and view all the answers

What effect does direct lighting usually have on illuminated objects?

<p>It produces strong shadows and highlights on the objects. (A)</p> Signup and view all the answers

What type of luminaires is suggested for coated, light-screened VDUs?

<p>Minor or prismatic luminaires. (A)</p> Signup and view all the answers

In environments with high ceilings, what type of lighting is recommended?

<p>A combination of direct and indirect lighting. (B)</p> Signup and view all the answers

What is critical to examine when using direct lighting with dark screens?

<p>The brightness level of the ceiling. (D)</p> Signup and view all the answers

What is the impact of very uniform lighting provided by indirect lighting?

<p>It avoids creating any shadows. (A)</p> Signup and view all the answers

Why is the illuminance level at the workstation important?

<p>It impacts visibility and comfort during tasks. (D)</p> Signup and view all the answers

What is a characteristic of indirect lighting in low-ceilinged areas?

<p>It leads to uneven ceiling brightness. (C)</p> Signup and view all the answers

What should the luminaire screening provide when using dark-screen monitors?

<p>A very directional downward light distribution. (D)</p> Signup and view all the answers

What is the minimum recommended luminance ratio for effective visual tasks?

<p>1:1 (C)</p> Signup and view all the answers

What is the permissible glare index for an office space?

<p>19 (C)</p> Signup and view all the answers

Which surface has the highest recommended reflectance for optimal lighting?

<p>Ceiling (A)</p> Signup and view all the answers

How does glare affect visual comfort?

<p>It causes discomfort or reduces the ability to see. (C)</p> Signup and view all the answers

What is the luminance range for task areas recommended for effective lighting?

<p>100-300 cd/m2 (A)</p> Signup and view all the answers

Which factor does NOT affect the choice of lamp colour appearance in an office?

<p>Room temperature (A)</p> Signup and view all the answers

What is the recommended reflectance for floors to ensure adequate lighting conditions?

<p>0.1-0.3 (A)</p> Signup and view all the answers

What happens to the glare index when it increases?

<p>It increases discomfort glare. (D)</p> Signup and view all the answers

Which of the following luminance levels is NOT recommended for walls?

<p>300 cd/m2 (B)</p> Signup and view all the answers

What can occur if the luminance is too low in an office environment?

<p>Reduced visual performance for conventional work (B)</p> Signup and view all the answers

What is the optimum illuminance for dark screens in an office setting?

<p>250 lux (B)</p> Signup and view all the answers

What type of lighting arrangement is best for general offices with changing layouts?

<p>Surface or recessed luminaires in a fixed pattern (A)</p> Signup and view all the answers

Which type of desk lamps are considered unsuitable for office environments?

<p>Incandescent lamps with high heat emission (D)</p> Signup and view all the answers

How should desk-mounted reflector luminaires be positioned for optimal lighting?

<p>Higher than 0.6m above the desk-top (A)</p> Signup and view all the answers

What should be the primary focus when designing office lighting?

<p>Meeting individual visual requirements without disturbing others (B)</p> Signup and view all the answers

Which luminance characteristic is crucial for preventing visual adaptation issues?

<p>Controlling excessive differences in luminance (B)</p> Signup and view all the answers

What is the recommended average illuminance for non-working areas compared to working areas?

<p>Not less than 50% of working area levels (B)</p> Signup and view all the answers

How should lighting be adjusted to ensure an environment conducive to productivity?

<p>Allowing individual control over lighting levels from workstations (A)</p> Signup and view all the answers

What is the key consideration to avoid glare in office settings?

<p>Minimizing the use of reflective surfaces (A)</p> Signup and view all the answers

What illuminance ratio must not exceed 5:1 between two adjacent areas?

<p>The average illuminance of a corridor and an office (B)</p> Signup and view all the answers

What effect might excessively large differences in luminance have in an office?

<p>Lead to discomfort and glare for occupants (D)</p> Signup and view all the answers

What is the primary advantage of installing a system of general lighting in offices with flexible layouts?

<p>It ensures consistent illumination regardless of furniture arrangement. (A)</p> Signup and view all the answers

Which lighting option is least effective for achieving an even luminance distribution over a task area?

<p>Incandescent lamps in decorative desk lights. (A)</p> Signup and view all the answers

What should be considered when planning the layout of luminaires in an office designed for future partitioning?

<p>The potential modular structure of the building. (A)</p> Signup and view all the answers

What is an important characteristic of the recommended T5 luminaires for general office lighting?

<p>They require less maintenance compared to conventional lighting options. (B)</p> Signup and view all the answers

Why is it important to maintain consistent luminance between documents and screens?

<p>To prevent adaptation problems and ensure visual performance. (A)</p> Signup and view all the answers

What is the preference for colour temperature in warmer climates?

<p>High colour temperatures for a cool appearance (C)</p> Signup and view all the answers

Which color rendering index (Ra) is recommended for optimal office lighting?

<p>Ra of 80 (D)</p> Signup and view all the answers

What is the recommended colour temperature range for an intermediate appearance?

<p>3300 - 5300 K (B)</p> Signup and view all the answers

How can reflections on VDU screens be minimized effectively?

<p>By careful planning of light source positions (A)</p> Signup and view all the answers

What is a potential drawback of mixing light sources with different colour appearances?

<p>Decreased visual performance (B)</p> Signup and view all the answers

What type of lighting is suggested for achieving equal brightness on walls and furniture?

<p>Good indirect lighting with uplighters (C)</p> Signup and view all the answers

What colour appearance is indicated for color temperatures less than 3300 K?

<p>Warm (reddish white) (D)</p> Signup and view all the answers

Which statement correctly describes the relationship between lighting levels and color temperature preferences?

<p>Higher lighting levels prefer higher colour temperatures (A)</p> Signup and view all the answers

What effect does good indirect lighting have on VDU workstations?

<p>Allows for flexible positioning of workstations (B)</p> Signup and view all the answers

What is an additional feature to consider when planning lighting for VDU workstations?

<p>Position of VDU screens relative to light sources (C)</p> Signup and view all the answers

What disadvantage is associated with using indirect lighting in a workspace?

<p>It leads to uneven ceiling brightness. (C)</p> Signup and view all the answers

Why is direct lighting considered more efficient compared to indirect lighting?

<p>It requires less maintenance. (B)</p> Signup and view all the answers

What is a critical requirement for luminaire screening when using dark-screen monitors?

<p>It should ensure a very directional downward light distribution. (D)</p> Signup and view all the answers

What visual effect is commonly produced by direct lighting on illuminated objects?

<p>High contrasts creating highlights and deep shadows. (B)</p> Signup and view all the answers

In office settings with high ceilings, why might pendant luminaires be chosen?

<p>They combine direct and indirect lighting effectively. (D)</p> Signup and view all the answers

What might be a consequence of using indirect lighting in terms of maintenance?

<p>Quicker accumulation of dust on luminaires and ceilings. (A)</p> Signup and view all the answers

Which lighting arrangement is most likely to create a sombre impression in a workspace?

<p>Direct lighting with high contrasts. (B)</p> Signup and view all the answers

How does indirect lighting impact the efficiency of a lighting installation?

<p>It reduces the overall brightness in the space over time. (C)</p> Signup and view all the answers

What factor influences the degree of freedom in the placement of VDUs under direct lighting?

<p>The type of monitors used. (B)</p> Signup and view all the answers

What is a potential visual drawback of very uniform lighting?

<p>It can create a visually monotonous environment. (C)</p> Signup and view all the answers

What is the permissible glare index for office spaces to prevent discomfort in vision?

<p>19 (B)</p> Signup and view all the answers

Which surface has the recommended reflectance range of 0.5-0.7 for optimal lighting conditions?

<p>Walls (C)</p> Signup and view all the answers

What luminance ratio should be maintained between the visual task and its immediate background for effective seeing?

<p>Greater than 1:1 but less than 3:1 (C)</p> Signup and view all the answers

According to the recommended luminances, what is the appropriate range for ceiling luminance?

<p>100-300 cd/m2 (B)</p> Signup and view all the answers

Which of the following statements best describes the concept of glare?

<p>A state of vision caused by excessive contrast and extreme luminance. (C)</p> Signup and view all the answers

What is the recommended reflectance range for window shades to ensure adequate lighting control?

<p>0.4-0.6 (A)</p> Signup and view all the answers

What factors influence the choice of lamp color appearance in an office?

<p>Illuminance level and personal preference (A)</p> Signup and view all the answers

At what luminance level is task area lighting recommended in candelas per square meter (cd/m2)?

<p>100-300 cd/m2 (C)</p> Signup and view all the answers

Which surface has the lowest recommended reflectance to ensure adequate lighting conditions?

<p>Floors (B)</p> Signup and view all the answers

Flashcards

Office Lighting Levels

Recommended illuminance levels for office work on a horizontal surface (0.75m-0.85m from floor).

Individual Lighting Control

Ideally, individual workers should adjust lighting at their desk or workstation, either with dimming or switching.

Lighting Uniformity

The difference between minimum and average illuminance (Emin/Eav) should ideally greater than 0.8 in general lighting.

Non-Working Area Lighting

In localised or mixed lighting, non-working areas should have illuminance at least 50% of the working areas (minimum 350 lux).

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Adjacent Area Lighting Ratio

The ratio between the average illuminance of two adjacent areas (e.g., office and corridor) should not exceed 5:1. The area with lower level should have at least 150 lux.

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Visual Adaptation Problems

Large differences in luminance (brightness) in an office can cause problems adapting to the changing light levels.

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Working Plane

The horizontal surface at a height of 0.75m - 0.85m above the floor level, where most office work is done.

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Luminance Ratio

The ratio of light intensity between an object and its background.

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Optimal Luminance Ratio

The luminance ratio between a task and its background should be between 1:1 and 3:1.

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Glare

Discomfort or reduced vision due to excessive brightness or too many contrasts.

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Glare Index

A measure of discomfort glare in a lighting setup.

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Permissible Glare Index (Office)

Maximum allowed glare index for an office environment, typically 19.

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Surface Reflectance

The percentage of light a surface reflects.

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Recommended Luminance (Walls)

Luminance values for walls, typically between 50 and 150 cd/m2.

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Recommended Luminance (Ceiling)

Luminance values for ceilings, typically between 100 and 300 cd/m2.

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Lamp Color Appearance

The perceived color of a lamp, which depends on factors like illuminance and daylight.

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Colour Temperature (CCT)

A measure of the colour appearance of a light source, often described as warm (low CCT), cool (high CCT), or intermediate (mid-range CCT).

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Cool Colour Appearance

Light sources with a colour temperature above 5300K appear bluish-white.

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Warm Colour Appearance

Light sources below 3300K appear reddish-white.

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Colour Rendering Index (Ra)

A measure of how well a light source renders colours in comparison to a natural light source like daylight. A higher value means better color representation.

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Preferred Colour Temperature

Higher colour temperatures are preferred in higher lighting levels and daylight, while lower colour temperatures are preferred in low-light situations and in warmer climates.

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VDU Workstation Lighting

Lighting for Video Display Units (computers) needs to minimize reflections on the screen.

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Reflections (VDU)

Light reflecting off surfaces, like windows or light fixtures, onto the VDU screen, impairing readability.

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Indirect Lighting

Artificial lighting that is diffused and scattered to avoid creating bright spots which reflect on the VDU screen.

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Uplighters

Lighting fixtures that project light upwards, often used in indirect lighting systems for VDU workstations.

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Recommended Ra Value for Offices

A colour rendering index of at least 80 is recommended for all office lighting. This ensures good color rendering and clarity.

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Optimal Illuminance

The ideal brightness level for office work, typically between 400 lux for light screens and 250 lux for dark screens.

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General Office Lighting

A system of fixed luminaires arranged regularly over the ceiling to provide consistent illumination throughout the office.

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Flexible Office Lighting

Lighting systems that allow for adjustable brightness and localized illumination for various tasks.

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Task Lighting

Supplementary lighting focused on specific work areas to improve visual comfort and performance.

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Desk Lamp Suitability

Desk lamps should be well-designed, emit minimal heat, and provide even light distribution.

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Indirect Lighting Disadvantage

Indirect lighting, where light bounces off the ceiling, can lead to faster dirt accumulation on the luminaires and ceiling due to warm air currents carrying dust upwards. This reduced lighting level also reduces the efficiency of the installation.

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Low Ceiling Problem

In low-ceilinged areas, indirect lighting creates uneven brightness on the ceiling, leading to reflections in computer screens.

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Shadowless Environment

Indirect lighting provides very uniform lighting, resulting in a lack of shadows, which can feel unnatural.

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Direct Lighting Advantages

Direct lighting is generally more efficient and less prone to dirt accumulation compared to indirect lighting. It also allows for heat dissipation through the ceiling, minimizing the heat load in the room.

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Direct Lighting and Screens

Direct lighting requires careful luminaire screening to prevent reflections on computer screens, especially with dark-screen monitors.

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Direct Lighting and Screen Types

Light-screened computer monitors allow for broader light distribution from direct luminaires without causing reflections.

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High Ceiling Lighting

For high ceilings, pendant luminaires combining direct and indirect lighting offer a suitable alternative for both dark and light screens.

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High Ceiling Considerations

Even with high ceilings and mixed lighting, it's crucial to ensure even brightness and proper screening of the direct light component to minimize screen reflections.

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Illuminance Level Importance

Choosing the right illuminance level at workstations is crucial for comfortable and efficient work.

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Illuminance Level Definition

Illuminance refers to the amount of light falling on a surface, measured in lux. It's an important factor in office lighting design to ensure adequate and comfortable working conditions.

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Luminance Differences

Large differences in luminance (brightness) in an office can cause visual adaptation problems, while too small differences can make the environment seem dull.

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Color Temperature

A measure of how warm or cool a light source appears. Measured in Kelvin (K).

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Recommended Illuminance Levels

Suggested brightness levels for different office tasks and activities.

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What is the optimal illuminance for office work?

The optimal illuminance lies between 400 lux for light screens and 250 lux for dark screens, striking a balance between visual performance and character contrast.

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What are the two main types of office lighting?

There are general (fixed) lighting, where luminaires are installed in a regular pattern, and flexible lighting, which allows for adjustable brightness and localized illumination.

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What is the key benefit of flexible office lighting?

Flexible office lighting can achieve energy savings by allowing people to adjust the lighting to their needs, reducing overall use.

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What are the drawbacks of desk lights with incandescent lamps?

Desk lights with incandescent lamps are insufficient, emit excessive heat, and create uneven light distribution, making them unsuitable for office work.

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What are the benefits of using (compact) fluorescent lamps in office lighting?

(Compact) fluorescent lamps provide broader and more even light distribution, negligible heat emission, and eliminate glare, making them ideal for office lighting.

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Study Notes

Lighting for Offices and Educational Buildings

  • People spend significant time on phones, computers, and communicating in offices
  • Lighting design should consider visual tasks and contribute to well-being
  • General lighting levels recommended for average office tasks (0.75m-0.85m above floor level) are in IS:3646 (Part-II) 1992.

General Recommendations

  • Illuminance levels vary based on task.
  • Individuals need control over lighting to suit their needs without disturbing others
  • For general lighting, the minimum-to-average illuminance ratio (Emin/Eav) should be >0.8
  • Local (or localised) general lighting should meet 50% of working area illuminance minimum 350 lux
  • The ratio between adjacent areas shouldn't exceed 5:1
  • The area with lower illuminance should have at least 150 lux

Luminances

  • Large luminance differences create visual adaptation problems or glare.
  • Small differences lead to dull, uninteresting surroundings
  • Luminance ratio between task (e.g., desk) and immediate background (e.g., wall) should be between 1:1 and 3:1 (inclusive)
  • Walls: 50-150 cd/m²
  • Ceiling: 100-300 cd/m²
  • Task area: 100-300 cd/m²

Glare Control

  • Glare occurs when lamps, luminaries, windows, or other areas are too bright compared to surrounding brightness.
  • Glare causes discomfort or impairs vision
  • A Glare index of 19 is acceptable for an office setting.
  • Glare increases with higher Glare index
  • Glare can be reduced by adjusting the spacing of lights, and surface (reflection) factors

Lamp Colour

  • Lamp colour choice depends on illuminance level, daylight availability, climate, and personal preference

  • Lamps are categorized by correlated colour temperature (CCT)

  • Cool (bluish white): > 5300K

  • Intermediate (white): 3300-5300K

  • Warm (reddish white): < 3300K

  • Higher CCT (colder light) is preferred at higher illuminance levels (more light)

  • Lower CCT (warmer light) is preferred in the absence of daylight (less light).

  • Colour sources should match to avoid colour mismatch

Lighting for VDU Workstations

  • VDU screens reflect light sources (lamps, windows, etc).
  • Indirect lighting helps minimize reflections.
  • Direct lighting, while more efficient, may create harsh shadows.
  • Dark screen VDUs require luminaires suited for minimal reflection

Illuminance Levels

  • Recommended illuminance for VDU workstations is 400 lux for light screens and 250 lux for dark screens.

Office Types

  • General offices often have flexible layouts.
  • Ceiling mounted luminaires can be used for consistent lighting
  • Flexibile lighting (switching and dimming, task lighting) allows for energy savings
  • Desk-mounted luminaires with fluorescent lamps distribute light evenly, efficiently and have low heat emission
  • Drawing offices require higher illuminance (1000 lux) to differentiate fine details.
  • Disturbing shadows and glare are avoided in drawing offices using diffused light sources

Educational Buildings

  • Lighting in educational settings must promote learning
  • Day light should be incorporated where possible.
  • Low brightness or well-screened ceiling luminaires are better for class rooms

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