Daylighting your house

Arguably one of the most important considerations when designing new buildings is energy efficiency; and a lot of that relates to how many lights need to be turned on to illuminate the interior. And as we build at higher densities, and try to meet strict thermal insulation requirements, architects are having to think even more creatively about how to make the maximum use of free lighting, in the form of natural daylight. From MIT, Christoph Reinhart...

Christoph - Daylight is an important concept not only for architecture but for really, everybody. If you think back before the times when we had electric lighting in building, really daylight was a necessity the only source of us being able to see what is going on in building. Why daylighting is important nowadays, has actually two reasons. Well first of all, it tends to provide a better type of lighting than electric lighting. It's because the colours of daylighting come out more vividly.  When daylight shines on objects, you can see them better. Now, another benefit of daylighting is of course that if we have a room without a window then we have to turn on the electric light and that takes a lot of energy if we use the daylight that comes for free.

Chris - What about human physiological impact as well? Are humans better off under daylight than under artificial light?

Christoph - Yeah, it's very good that you're asking that question. So, we've known for a long time that visual rendering of objects are better with daylight because it comes in all colours of the rainbow. So, they render the colour of that object very well. Something else that's very exciting that we only found out really within the last decade is that daylight not only provides us visual information about the world around us, but it also is linked to something that's called our circadian rhythm, so our biological clock. What that concept means really is that all of us, in our brain, we have a little clock that tell us what time it is. If we wouldn't get any clues from the outside world, through light, what time it is, then we would start drifting. Some of us would have maybe 25-hour days, others would have 23-hour days. So daylight, it's very important in training us, basically keeping us all synchronised that we can all follow our lives at the same time.

Chris - But equally, is it possible to end up with too much daylight exposure if you're working in a building and care is not taken. Could you end up with over lighting of the interior?

Christoph - Well, absolutely. That can happen. So, architects and owners think, the more, the better. So, if we just open our buildings, have a fully glazed facade then we get more daylight and it's necessarily better. But that's actually not the case because once we have too much daylight and we want to read a book or do something on an electronic device such as an iPad or a computer, then we might be in situations where we can't see because there's too much light. Basically, what there is, is really too much contrast. That means if you are in a room that is partly very, very bright to sunlight and then when you look in the back of the room, it's very dark, then our eye cannot adapt, cannot take in this large range of brightness variances and that's called glare, that leads to discomfort.

Chris - So, do architects have mechanisms to predict how much light is going to penetrate into a building, what the likelihood of glare occurring is and therefore, how to mitigate it?

Christoph - There are methods in place. So, especially over the last couple of decades, we've had made in the architectural world a lot of advances in modelling buildings in a computer. So, it's as if we are putting a building into something like a computer game from the gaming industry and then we can model the light for a whole year that shines on the building. So, we have become very good at predicting how much light there is in buildings.

Chris - Equally, does the same apply when trying to get light into a building? So, formatting the interior correctly so that you can get as much light as possible as deep into your building structure as possible. So, it's not just the people who sit by the windows that are well lit.

Christoph - Yes, that's a very good question. What is very important is how high the upper edge of the window is. So, if you're in a space right now, you're looking at the window, you really want to have the distance between the floor and the upper edge of the window as high as possible. So then you can basically get away with a window that takes maybe a third or so of the whole facade, the rest is just wall. But if the window is like a band of light which is close enough to the ceiling that on the one hand it allows you to look outside, but also, it's high up. Then it penetrates light very deep into the space.

Chris - Now, we're talking here about individual buildings, but often developments occur as whole clusters of buildings. So, is there any way or any tools available for architects to be able to format whole cities even so that they make the maximum use of available light and they minimise their cooling bills, they minimise their heating bills in order to be as energy efficient and light efficient as possible?

Christoph - Legislation has been in place for a long time. Arguably, one of the first legislations in the field of access to light at the street level and then buildings comes from 1917. These were the ordinances in New York city that when all the skyscrapers were being built in Manhattan that stipulated how much offset buildings have to have from the street so that there's sufficient light both on the street level as well as on the buildings. And these were really what we would call section base. So, it's as if you draw in 2 dimension a city on a piece of paper, just the outline. You don't really think 3-dimensionally of the problem. You just see two buildings next to each other that form an urban canyon.

Nowadays, due to advances in computer rendering and just availability of data on cities, what we've been working on in our lab is an urban modelling platform called 'Umi' and what this allows is that we can effectively use data that are available for many cities which are called geographic information systems that contain information about the form, the shapes of any building in the city that usage pattern, the existence of trees around it, the value of the building and so forth. So, we can take these big databases and convert them into energy and lighting simulation programmes and scenes, run simulations of lighting and energy for whole city and then provide that back to the city. So, they can then use this information for example to have better policies of how much distance between buildings have to exist when you go away just from the daylighting and look more at energy use in buildings. We can then use this for policy measures to say, what are the most offending buildings in our neighbourhood that use too much energy? How can we help these buildings save energy for the whole city?