What is the Daylight Factor (DF)?

It's the ratio of the light level inside a building to the light level outside on an overcast day, expressed as a percentage. (Clause 2.4)

What is the recommended daylight factor for general assembly work in a factory?

A minimum daylight factor of 3% is recommended for medium work such as general assembly lines. (Table 1)

Which type of rooflight is best for factories?

North-light roofs are generally preferred for factory bays as they provide high levels of diffuse, glare-free light without significant solar heat gain. (Clause 5.3.1)

Does this code account for electric lighting?

No, this code deals exclusively with natural daylighting. Integration with artificial lighting is covered in other codes like IS 3646.

IS 6060

: 1971

Code of Practice for Daylighting of Factory Buildings

CurrentSpecializedCode of PracticeBIMArchitectural · Functional Requirements in Buildings

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This code of practice provides recommendations for the daylighting of factory buildings to ensure adequate natural light for visual tasks and a comfortable working environment. It specifies minimum daylight factors for various industrial activities and gives guidance on the design of windows, rooflights, and other fenestration.

Code of Practice for Daylighting of Factory Buildings

Quick Reference Values

Minimum Daylight Factor for rough work (e.g. storage)2%

Minimum Daylight Factor for medium work (e.g. assembly)3%

Minimum Daylight Factor for fine work (e.g. fine machining, inspection)5%

Daylight Factor for very fine work (e.g. watchmaking)10%

Basis for calculationStandard Overcast Sky with 5000 lux outdoor illuminance

Key Formulas

Daylight Factor (DF) = (Ei / Eo) x 100 — Ratio of internal point illuminance to simultaneous external unobstructed illuminance.

DF = Sky Component (SC) + Externally Reflected Component (ERC) + Internally Reflected Component (IRC)

Practical Notes

This code is quite old; modern daylighting analysis is now predominantly done using computational simulation software (e.g., DIALux, Radiance, IESVE) which offers more detailed and accurate results.

The recommendations are based on a standard overcast sky, which is a conservative basis for design but may not reflect the predominant clear sky conditions in many parts of India.

Effective daylighting design requires a holistic approach, considering building orientation, shading strategies to control glare and heat gain, and the reflectance of interior surfaces, not just the window-to-wall ratio.