Theoretically, direct sunlight on outside wall surface penetrates into the room up to 20 ft., adequate enough for normal reading and such room activities.
Sunlight has been such a commonly studied aspect of building design that much before Autodesk launched its software programme Ecotect or many free download applications got introduced, people judged it by common sense. While those with access to computers may study the impact of sun in a tech savvy way, the rest need to continue with traditional wisdom. Incidentally, this wisdom continues to be very valid.
The challenges of designing for sunlight in South India are not all that simple, for the best light angle may bring in worst heat or bright glare. The starting point is to keep the longer face of the building to face north and south, wherein north lets in soft diffused light and south invites ample direct light which may have to be adequately shaded. Trees, verandah, projected walls and such others help in softening the south light. The shorter elevation facing east invites much needed morning light and the shorter west facing wall gets angular afternoon light which is not very harsh.
This orientation also invites glare, especially the evening one that can be troubling. To reduce it, the windows can be slightly angled, vertical sunshades can be introduced or simply the openings can be avoided. The morning glare may not be so harsh and after 9 a.m., once the sun moves up, the glare can be managed with normal sunshade atop the window or minimal windows. The afternoon sun can brighten up the south sky so much, we may have to keep the curtains pulled, yet adequate diffused light may filter in.
Theoretically, direct sunlight on the outside wall surface penetrates into the room up to 20 ft., adequate enough for normal reading and such room activities. If the room has to be wider, say up to 40’, we need windows on both side walls to ensure good day light factor. Big and square plans should be avoided with preference for rectangular plans. However, there could be low light during cloudy days or when the sun is totally on one side. To help with more light, we can keep the total window area around 25 per cent of floor area, much higher than the suggested 15 per cent. Also, making the windows tall, taking them up to the roof, helps by letting deeper sunlight penetration.
Generally, bedrooms in the northern half, especially to east and west, are best to sleep — neither too bright light nor excessive heat. South-west provides good lighting for evening study, family interaction, home games and such others. It gets heated up to act as a heat sink during night hours. South-east gets good direct light during morning half and diffused light during the afternoons, making it suited for varied activities.
In compact city sites, it is not always possible to design for best light, for neighbouring buildings tend to shade each other. Also, designing for light may contradict the criteria for heat, rain or wind. As such, the better option is to accept some compromise, but get the better of all criteria.