The 1975 IS 2440 standard delivers detailed guidance on utilizing natural daylight in various building types including residences, offices, and hospitals. It sets out the minimum illumination requirements, adjustment factors for window glazing and obstructions, and design strategies to maximize daylight while controlling glare, tailored for Indian environmental and site contexts.
Overview
The 1975 IS 2440 standard delivers detailed guidance on utilizing natural daylight in various building types including residences, offices, and hospitals. It sets out the minimum illumination requirements, adjustment factors for window glazing and obstructions, and design strategies to maximize daylight while controlling glare, tailored for Indian environmental and site contexts.
Audience
Contents
Structure
This section outlines the extent of the standard, focusing on methods and tabulated data for computing the Sky Component (SC) of daylight through vertical windows under clear tropical skies. It covers the use of tables providing percentage SC values on horizontal and vertical planes relative to window orientation, essential for daylighting analyses in tropical climates.
Defines essential terms such as Sky Component, vertical window, and horizontal plane. It also explains the importance of three key tables for calculating percentage sky components on different planes and describes how to apply these tables for daylight and solar heat gain calculations.
Discusses factors impacting vision including the peripheral field's sensitivity to glare, how window dimensions relate to daylight factor requirements, the relationship of sky component percentages to distance from windows, and guidelines for ensuring visual comfort through brightness and contrast management.
Explains the primary sources of daylight, emphasizing sky radiation over direct sunlight for indoor illumination. It highlights glare sources and recommends mitigation techniques such as louvers, shading devices, and cross-lighting strategies to ensure comfortable interior lighting.
Describes the three components that make up the daylight factor: sky component, externally reflected component, and internally reflected component. It details correction factors for external reflections based on elevation angles, the influence of internal surface reflectances, and provides solar altitude data relevant for Indian latitudes.
Defines daylight factor with relevant formulas, establishes a baseline for external illumination (typically 8,000 lux in India), and lists recommended daylight factor percentages for various building spaces. It also discusses how daylight factor relates to indoor illumination design.
Covers principles for dimensioning and positioning windows to achieve desired daylight factors. It introduces key geometric ratios (half-window width to distance, window height to distance) used in selecting window sizes from tables, and stresses the importance of adjusting sky component values to account for glazing and obstructions.
Focuses on the relationship between building height and spacing to maximize daylight penetration, supported by tabulated data illustrating relative daylight availability for different block configurations. It recommends minimum spacing ratios and highlights the benefits of light-colored interior surfaces.
Details step-by-step instructions for calculating sky component percentages using window dimensions and distances to points of interest. It provides example calculations and guidance on interpreting and interpolating values from the relevant tables for accurate daylight factor estimation.
Introduces the concept of sky component and presents the three key tables used for calculating sky component percentages on horizontal and vertical planes relative to vertical windows. It explains how to combine these values for any plane and notes their applicability under tropical sky conditions.
Provides formulas and example calculations for determining window dimension ratios and applying tables to find sky component values. It offers procedural steps and illustrative cases to facilitate accurate daylight factor computations.
Summarizes the standard’s key recommendations on daylighting, including scope, window sizing based on desired daylight factors and light penetration depths, and the use of percentage sky component curves. It also references related standards for factories and educational buildings.
Frequently Asked
IS 2440 specifies that for glazed windows, sky component values should be reduced by 10% to 20% for clear glass and by 15% to 30% for frosted or ground glass, with higher corrections applied for larger windows or points near the reference. External obstructions require considering only the unobstructed window area when reading sky component values, effectively reducing daylight proportionally to the obstruction coverage.
The daylight factor is defined as the percentage ratio of indoor illuminance at a point to the simultaneous outdoor illuminance under an overcast sky, excluding direct sunlight. It is calculated as the sum of three components: sky component (direct sky light), externally reflected component (light reflected from outdoor surfaces), and internally reflected component (light reflected within the room).
The standard refers to IS 3646 (Part II)-1966 for illumination levels, recommending lighting intensities based on the task type: fine tasks require 500 to 1000 lux, medium tasks 200 to 500 lux, and coarse tasks 100 to 200 lux. It emphasizes maintaining brightness ratios of task area to immediate surroundings to distant areas as 10:3:1 to prevent visual discomfort.
Glare reduction is achieved by shielding direct bright sky views with louvers, external hoods, or deep window reveals. Additionally, cross-lighting surrounding walls to create uniform brightness and ensuring gradual transitions in brightness within the visual field help reduce discomfort caused by excessive contrast or abrupt changes in luminance.
IS 2440 advises that building height and spacing must be coordinated to optimize daylight penetration, recommending minimum separation distances generally between 1.5 to 2 times the building height, depending on the layout. It also highlights that parallel blocks facing gaps allow higher daylight availability and that light-colored interior surfaces improve illumination through increased reflectance.
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