Let there be Light!

Daylight has two natural sources. One of them is the sun providing sunlight, and the other source is the sky providing skylight. An illuminance of 1,00,000 lux is produced, when on a sunny day, 1,00,000 lumens strike 1 square metre of a building envelope. Theoretically, the daylight efficiency is at 100 percentage then it produces luminous energy enough to light 100 square metres at 1000 lux. A successful daylighting strategy is to optimise the distribution system efficiency and minimize the size of the collecting area. The efficiency of the system is linearly proportional to the size of the collecting area. 


There are two groups of daylighting strategies. The first type is where the light is brought from the sides of a building into the interiors referred to as a side-lighting system, for example, a window. The second type is where the light is brought inside from the top of a building, referred to as a top lighting system, for example, a skylight.

Daylighting design is about controlling the light levels along with the direction and the distribution of the light.

Side-lighting system

This system functions by decreasing excess daylight levels near the windows and increasing them away from the window, resulting in a more balanced daylight distribution throughout the interiors.

Light shelves, prisms or mirrored louvres, if added to the window glazing offers a more viable side-lighting system, as these devices help deflect the light further into the room and away from the window.

Side window

A side window compromises a visual element (window) and a non-visual element (clerestory). Typically, side windows incline to generate excessively lit areas near the window and dimmer areas elsewhere, especially when the room is deep.

The factors that affect the spread and depth of the daylight infiltration include sky conditions, the window orientation, the window location within the wall and to the rest of the room, the effective window height (from the sill to the upper limit of the window), and its width.

A discomforting glare is caused by a single side window because of the contrast between the window brightness and the darker background nearby the window aperture. Bringing daylight from two different sides produces a deeper, more balanced daylight distribution and reduces glare.

Clerestory system

A clerestory is a side window that is placed higher in the wall. Generally, it doesn’t provide any views to the outside but helps permit daylight inward into the room while giving little glare discomfort to the occupants.

Similar to a side window, when placed on the south-facing wall, it will generate higher daylight illumination than a one on the north side. East and west-facing are hard to shade and have potentially more heat gains. The daylight zone depth relies on the mounting height of the clerestory (distance from the floor to the bottom of the aperture) and the width and length of the clerestory itself. 

We can combine a side window and a clerestory system which provides a more balanced distribution of daylight.  

Light shelf system

A light shelf device is to capture daylight, particularly sunlight, and redirect it to the back of the room by ceiling reflection. This strategy provides more even distribution of light throughout the room than is found in a room with only a side window.


The light shelf has two parts, the lower part serves to provide views like a side window, and the upper part helps to redirect the daylight to the back of the room. A light shelf can also provide shade from direct sunlight and reduce glare from the sky. Its size and depth depend on window size and façade orientation.

Louvre systems

Louvre systems are dynamic or static, designed to collect the sunlight falling in the front of the room and redirecting it towards the back. Thus, increasing daylight levels in the back and reducing them in the front of the room.

Automated Dynamic system control to follow the sun’s movement in the sky. Automatic louvres tend to have better performance than static; however, they require a calibration system that needs alteration according to the illumination building needs, along with the heating and cooling requirements to admit the correct expanse of sunlight.  

Prismatic systems

Prismatic glazing changes the direction of the sunlight and uses refraction and reflection to redirect into the room. Refraction alters the direction of the incident ray of light of the prism. A part of it is then further reflected upward towards the ceiling and onward towards the back of the room.

However, its practical application to yield and regulate light distribution in building interiors is limited, and its performance viability still undergoing research and further exploration. 

Skylight system

The straightforward top lighting strategy is a skylight. Typically, it uses a horizontal or an inclined opening in the roof of the building. It collects sunlight when the sun is high in the sky.

The skylight diffuses the collected light from the sky vault’s zenithal area and introduces it into the room under the skylight. It is applicable only on the top floor of a multi-storey or single-story building.

Roof monitor and sawtooth systems

The top lighting systems Roof monitors and sawtooth systems primarily differ in their shapes. Like the skylight, light apprehends through vertical or sloped openings in the roof.


It captures light at certain times of the day or year, as per the building requirements.

Light pipe system

A top lighting strategy is a light pipe system designed to bring daylight to the lower floors of a multi-story building. They have 3 parts-

  • A light collector: collects ambient light from all directions and delivers it to the internal unit.
  • A light pipe: a reflective system that transfers the light to various locations with minimum light loss.
  • Light Diffuser: distributes the collected light indoors.

Why do we need an effective daylight system?

We spend most of our time through the day indoors and are unable to receive an adequate amount of sunlight. Thus, buildings need to admit a well-balanced light level. High daylight levels enhance the secretion of serotonin and keep us alert. Daylight also acts as an effective antidepressant.

A well-designed daylight system provides significant energy, thus cost-saving for the occupant. The absence of proper sunlight has repercussion on the occupant’s overall health. It proves toxic because of a deficiency of vitamin D in our bodies. Buildings design should maximize our exposure to sunlight; to further facilitate the cutaneous photosynthesis that caters to our vitamin D needs. So, soak up the sun. 

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