Guide for Daylighting of Buildings

IS 2440 - Scope: Sky Component Tables & Calculations

The code provides tables and methods to calculate the Sky Component (SC) for daylighting analysis through vertical windows under a tropical clear sky.

Key Points:

• Scope:
  Applies to unglazed openings illuminated by the clear tropical design sky.

• Tables Included (Appendix A):

  1. Table 5: Sky component (%) on the horizontal plane due to a vertical window.
  2. Table 6: Sky component (%) on the vertical plane perpendicular to a vertical window.
  3. Table 7: Sky component (%) on the vertical plane parallel to a vertical window.

• Calculation Method (Appendix B):
  Use the tables to find percentage SC values based on window orientation and plane of interest.

Typical Formula for Sky Component (SC):

[ SC = \frac{E_{i}}{E_{o}} \times 100 ]

• (E_i): Illuminance at the point inside due to sky
• (E_o): Illuminance outside under an unobstructed sky

Summary Table Example (Conceptual):

flowchart LR
    A[Start: Identify Window Orientation] --> B{Select Plane}
    B --> C[Horizontal Plane (Table 5)]
    B --> D[Vertical Perpendicular Plane (Table 6)]
    B --> E[Vertical Parallel Plane (Table 7)]
    C --> F[Find % SC from Table 5]
    D --> G[Find % SC from Table 6]
    E --> H[Find % SC from Table 7]
    F & G & H --> I[Calculate SC & Apply in Daylighting Design]

Use these tables and methods to accurately estimate daylight availability through vertical openings under tropical sky conditions.

IS 2440: Definitions & Key Tables for Sky Component Calculation

Key Definitions (Clause 2.0)

• Sky Component (SC): Portion of the sky visible from a point inside a room through a window, expressed as a percentage.
• Vertical Window: Window plane oriented vertically.
• Horizontal Plane: Plane parallel to the floor at the observer's eye level.

Important Tables (Appendix A & Clauses 5.3.x)

Usage Notes (Appendix B)

• Use these tables to find percentage sky components for daylighting and solar heat gain calculations.
• Tables provide values for the tropical design sky conditions.
• Sky component values are used in formulas for daylight factor and solar radiation calculations.

Formula for Sky Component (SC)

[ SC = \frac{\text{Visible sky area through window}}{\text{Total sky hemisphere}} \times 100% ]

Summary Diagram of Planes & Orientations

graph TD
    A[Observer Point] -->|Horizontal Plane| B(Horizontal Plane)
    A -->|Vertical Plane Perpendicular| C(Vertical Plane ⟂ Window)
    A -->|Vertical Plane Parallel| D(Vertical Plane || Window)
    E[Vertical Window] --> C
    E --> D

This framework helps determine daylight availability and solar exposure through windows as per IS 2440.

IS 2440: Factors Affecting Vision – Key Points & Formulas

1. Peripheral Field (Clause 2.22)

• Peripheral field subtends ~30° on either side of fixation.
• Central peripheral field is sensitive to glare perception.

2. Window Size & Daylight Factor (Clause 7.1.1)

• Window width and height determined from Appendix A tables based on:
  • Required Daylight Factor (DF) (see Table 3).
  • Depth of daylight penetration (3 options in 6.3.3).
• Adjust DF for glazing, external obstructions, or window bars (Clause 7.1.3).

3. Percentage Sky Component & Distance from Window

• Sky component curves (Fig. 2) relate distance from window (cm) to sky component % on working plane.
• Used to estimate daylight availability inside a room.

4. Visual Comfort (Clause 3.1)

• Vision depends on brightness and color contrast.
• Central 2° field must be brighter and higher contrast for comfort.
• Uniform brightness in the whole field reduces eye strain.

Summary Table: Daylight Factor Adjustment (Example)

flowchart LR
    A[Daylight Factor (DF)] --> B[Window Size from Appendix A]
    B --> C[Width & Height]
    A --> D[Adjust for Glazing/Obstruction]
    D --> E[Effective DF]
    E --> F[Visual Comfort]
    F --> G[Central 2° Brighter & Contrasting]

Use these guidelines to optimize window design for adequate vision and glare control per IS 2440.

IS 2440: Sources of Daylighting – Key Points & Formulas

1. Sources of Daylighting (Clause 4.1)

• Primary source: Sunlight, comprising:
  • Direct solar illumination (excluded in design)
  • Sky radiation (used for interior daylighting calculations)
• Only sky radiation contributes to indoor illumination per IS 2440.

2. Glare Control (Clause 3.2.3)

• Glare mainly from bright sky views through windows.
• Minimized by:
  • Louvers, external hoods, deep reveals to shield direct sky view.
  • Cross-lighting surrounding walls for brightness uniformity.
  • Gradual brightness transitions reduce discomfort.

3. Window Design & Daylight Factor (Clause 7.1.1)

• Window size (width & height) depends on:
  • Desired Daylight Factor (DF) (see Table 3 in IS 2440).
  • Depth of daylight penetration (3 alternatives in Clause 6.3.3).
• Use Appendix A tables for window sizing based on DF and penetration depth.

4. Percentage Sky Component (PSC)

• PSC varies with distance from window (sill on working plane).
• Refer to Figure 2 for typical vertical cross-section curves of PSC.

Typical Daylight Factor Formula (general knowledge):

[ DF = \frac{E_i}{E_o} \times 100% ]

• (E_i) = illuminance at the interior point.
• (E_o) = simultaneous outdoor illuminance under overcast sky.

Summary Table (conceptual):

flowchart LR
    Sunlight -->|Direct solar (excluded)| NoInteriorLight
    Sunlight -->|Sky radiation (used)| InteriorLight
    InteriorLight --> WindowDesign
    WindowDesign -->|

IS 2440: Daylight Components and Corrections

1. Components of Daylight Factor (Clause 5.2.1.1)

Daylight Factor (DF) = Sum of three components, each expressed as % of simultaneous external horizontal illumination:

• Sky Component (SC): Direct light from sky visible through window.
• Externally Reflected Component (ERC): Light reflected from external surfaces.
• Internally Reflected Component (IRC): Light reflected from internal surfaces.

2. Correction Factors for ERC (Clause 5.4, Table 2)

3. Internal Reflected Component (IRC) (Clause 5.5)

• IRC ∝ (Window Area) / (Total Internal Surface Area)
• Depends on reflectance of walls, ceiling, floor, and outside ground.
• Whitewashed interiors increase IRC.
• External obstructions reduce IRC proportionally.

4. Solar Altitudes for Indian Latitudes (Clause 4.2, Table 1)

• Solar altitude angles (°) at various times and latitudes are provided.
• Useful for daylight design and shading calculations.

5. Window Sizing (Clause 7.1.1)

• Refer to Appendix A tables for window width/height based on desired daylight factor and room depth.

flowchart LR
    A[External Horizontal Illumination] --> B[Sky Component (SC)]
    A --> C[Externally Reflected Component (ERC)]
    B & C --> D[Window]
    D --> E[Internal Reflected Component (IRC)]
    E --> F[Daylight Factor = SC + ERC + IRC]

Summary:
Use the three daylight components with correction factors for ERC and IRC based on surface reflectances

IS 2440: Daylight Factor & Illumination Levels

Key Definitions

• Daylight Factor (DF):
  [ DF = \frac{\text{Indoor illuminance at a point}}{\text{Outdoor illuminance under overcast sky}} \times 100% ] (Clause 2.7)

• Design External Illumination:
  Assumed as 8,000 lux for India (Clause 4.3).
  Increase by 25% in hazy conditions.

Recommended Daylight Factor (%) for Interiors (Table 3, Clause 6.3.2)

Illumination Level Design

• Base external illumination: 8,000 lux horizontal plane (Clause 4.3)
• Internal illumination levels depend on task and location.
• Daylight factor relates internal illumination to this external reference.

Summary Formula for Internal Illuminance

[ E_{inside}

IS 2440: General Principles of Window Design for Good Daylighting

Key Points from Clauses:

• Clause 7.2: Window design should ensure adequate daylighting by selecting appropriate size and position.
• Clause 5.3.2: Values from tables apply to rectangular, unglazed windows without obstructions. Adjustments needed for glazing, bars, or external obstructions.
• Clause 7.1.1: Window width and height are chosen using tables in Appendix A based on:
  • Desired Daylight Factor (Table 3)
  • Depth of daylight penetration (Clause 6.3.3)

Important Parameters:

• l/d = Half window width / distance from working plane point
• h/d = Window height / distance from working plane point

Example: For a point 300 cm from window sill, window width 180 cm, height 150 cm:

• ( l/d = \frac{90}{300} = 0.3 )
• ( h/d = \frac{150}{300} = 0.5 )

Typical Use of Tables:

• Use Table 5 for sky component values at horizontal working plane points.
• Use Appendix A to find sky component curves (Fig. 2) and corresponding daylight factors.
• Adjust sky component for glazing, bars, and external obstructions as per Clause 5.3.2.

Summary Formula for Sky Component (SC):

[ SC = f(l/d, h/d) ]

where (f) is obtained from tables/graphs in Appendix A.

Diagram: Window Geometry Parameters

flowchart LR
    A[Window Width = 180 cm] -->|Half width = 90 cm| B(l)
    C[Distance from point to window sill = 300 cm] --> D(d)
    E[Window Height = 150 cm] --> F(h)
    B --> G[l/d = 0.3]
    F --> H[h/d = 0.5]
    D --> G
    D --> H

Note: Always correct sky component values for glazing and external obstructions for accurate daylight factor estimation.

IS 2440: Key Points on Siting of Buildings (Clause 8)

• Building height (H) and spacing (S) are interdependent; adjusting these optimizes daylight availability for any floor area ratio.

Table: Relative Daylight Availability at Ground Level (Clause 8.2)

• H = Building Height, S = Separation Distance

Additional Specifications:

• Internal surfaces should be light-colored with high reflectance to enhance diffused lighting (Clause 7.2.11).
• Window size and placement should follow daylight factor tables (Appendix A) and depth of light penetration guidelines (Clause 7.1.1).
• Percentage sky component curves (Fig. 2) help assess daylight penetration at various distances from windows.

Practical Formula for Minimum Spacing (S):

[ S \geq k \times H ]

where (k) is a factor (typically 1.5 to 2.0) depending on layout and daylight requirements.

flowchart LR
    A[Building Height (H)] --> B[Determine Separation (S)]
    B --> C{Type of Block Layout}
    C -->|Parallel Blocks| D[Use Table values for daylight]
    C -->|Facing Each Other| E[Use Table values for daylight]
    C -->|Facing Gaps| F[Use Table values for daylight]
    D & E & F --> G[Optimize spacing for daylight]

This ensures adequate daylight, ventilation, and comfort in building siting per IS 2440.

IS 2440: Calculation of Sky Component (Clause 5.4, Appendix B)

Key Points:

• Sky Component (SC) quantifies daylight from the sky through a window onto a working plane.
• Use Tables 5, 6, and 7 in Appendix A for % sky component values:
  • Table 5: Horizontal plane (most common for working planes).
  • Table 6: Vertical plane perpendicular to window.
  • Table 7: Vertical plane parallel to window.

Calculation Steps (Example from Clause 1.1):

Given:

• Distance from window, ( d = 300 , cm )
• Window width, ( w = 180 , cm ) (half-width ( l = 90 , cm ))
• Window height, ( h = 150 , cm )

Calculate ratios: [ l/d = \frac{90}{300} = 0.3, \quad h/d = \frac{150}{300} = 0.5 ]

Use these ratios to locate the sky component % from Table 5 (horizontal plane).

Summary Table (Example Format):

Notes:

• For typical daylighting design, use Table 5.
• For special cases (e.g., vertical planes), refer to Tables 6 and 7.
• The sky component is read directly from tables using ( l/d ) and ( h/d ).

flowchart TD
    A[Input Window Dimensions] --> B[Calculate l/d and h/d]
    B --> C[Refer to Table 5 (Horizontal Plane)]
    C --> D[Read % Sky Component]
    D --> E[Use in Daylighting Calculations]

This method ensures accurate daylight factor estimation per IS 2440.

IS 2440: Sky Component Tables Key Points

Sky Component Concept

• Sky Component quantifies the portion of sky visible from a point through a window.
• Used in daylight factor and lighting design.

Tables in Appendix A (Clause 1.1)

1. Table 5: % Sky Component on Horizontal Plane due to a vertical window.
2. Table 6: % Sky Component on Vertical Plane Perpendicular to the window.
3. Table 7: % Sky Component on Vertical Plane Parallel to the window.

Calculation Method (Clause 1.5, Appendix B)

• Calculate values from all three tables for the point of interest.
• Combine these values suitably to find the sky component in any plane passing through the point.

Important Notes

• These tables are for the tropical design sky conditions.
• Use window dimensions and point coordinates relative to the window for interpolation.
• Sky component values are expressed as percentages.

Example Formula for Sky Component (SC)

[ SC = f(\text{window size}, \text{point location}, \text{orientation}) ]

Where (f) is obtained by combining values from Tables 5, 6, and 7.

flowchart LR
    A[Point Location] --> B[Table 5: Horizontal Plane]
    A --> C[Table 6: Vertical Plane Perpendicular]
    A --> D[Table 7: Vertical Plane Parallel]
    B & C & D --> E[Combine Values]
    E --> F[Sky Component in Any Plane]

For detailed interpolation and usage, refer to Appendix B of IS 2440.

IS 2440: Calculation of Sky Component (Appendix B & A)

Key Formulas:

For a point P at distance d from the window, with window half-width l and height h:

[ l/d = \frac{\text{half window width}}{\text{distance to point}} \quad,\quad h/d = \frac{\text{window height}}{\text{distance to point}} ]

Example:

• Window width = 180 cm → half-width ( l = 90 ) cm
• Window height ( h = 150 ) cm
• Distance ( d = 300 ) cm
• Calculate:
  [ l/d = \frac{90}{300} = 0.3, \quad h/d = \frac{150}{300} = 0.5 ]

Procedure:

• Use Table 5 (Appendix A) for horizontal working planes to find the sky component based on ( l/d ) and ( h/d ).
• For complex cases (e.g., Example 12), use Tables 6 and 7 as well.
• Sky component values are interpolated from these tables.

Summary:

• Step 1: Calculate ( l/d ) and ( h/d ).
• Step 2: Refer to Table 5 for sky component values.
• Step 3: Use examples in Appendix B for guidance on reading tables.

flowchart TD
    A[Start: Point P distance d from window] --> B[Calculate l/d and h/d]
    B --> C{Use Table 5?}
    C -- Yes --> D[Find sky component from Table 5]
    C -- No --> E[Use Tables 6 & 7 for complex cases]
    D --> F[Apply sky component in daylight calculations]
    E --> F

This method ensures accurate daylight factor estimation per IS 2440.

IS 2440: General Notes on Daylighting

Key Points from IS 2440 (1975):

• Scope (Clause 1.1):
  Applies to dwellings, offices, hospitals; recommends minimum daylight illumination levels.

• Window Design Principles (Clause 7.2):
  Window dimensions (width & height) are selected based on:

  • Daylight Factor (DF) from Table 3.
  • Depth of daylight penetration (see Clause 6.3.3).
  • Refer to Appendix A for window size corresponding to DF and penetration depth.

• Daylight Factor (DF):
  [ \text{DF} = \frac{\text{Indoor illuminance due to daylight}}{\text{Outdoor illuminance under overcast sky}} \times 100% ]

• Percentage Sky Component (PSC):
  PSC curves (Fig. 2) show how sky visibility changes with distance from window sill on the working plane.

Typical Design Steps (Summary):

1. Select desired Daylight Factor (DF) from Table 3 for the space type.
2. Choose depth of daylight penetration (3 options in Clause 6.3.3).
3. Use Appendix A tables to find window width & height to achieve DF at given penetration.
4. Check Percentage Sky Component (PSC) for window placement and room layout.

Additional References:

• For factories: IS 6060-1971+
• For educational buildings: IS 7942-1976

flowchart TD
    A[Select Space Type] --> B[Choose Desired Daylight Factor (DF)]
    B --> C[Decide Depth of Daylight Penetration]
    C --> D[Refer Appendix A for Window Size]
    D --> E[Check Percentage Sky Component (PSC) Curves]
    E --> F[Finalize Window Design]

Summary: IS 2440 guides daylighting by linking window size to desired daylight factor and penetration depth, ensuring adequate natural illumination inside buildings.