Tuesday, January 19, 2010

Daylighting from Southern Windows

As I stated last time, southern windows get the most light throughout the day.  Also, that light is very harsh, very direct, and very high contrast.  So even though they get the most light, that light is the hardest to use to your advantage.  Here is a picture of my living room/entry early in the morning on a sunny day, the light is coming from a south facing window:

The effect is not that harsh in person, our eyes compensate better than the digital camera in my phone, but that contrast is real, not enhanced in any way.  Looking at the room like this will make your eyes tired from compensating for light and darkness, and this can make you feel tired and stressed after a few hours.

So what can we do?  Well let me show another picture, the same view taken the same time of day, but the sun has been obscured by some heavy clouds:

Much better, no?  The ceiling is still cave like, but the contrast on most stuff is very manageable.  This is because the cloud scatters the light, making it more diffuse.  It is the contrast that makes southern light so unpleasant.  To remove that harsh direct light and shadow, architects and engineers design elaborate shading devices (Courtney just finished designing one for a school project, actually) that only let in indirect light.  Adding something like that to an already finished building, however, is often impractical.  Furthermore, if you  are a tenant in an apartment or worker in an office, that kind of decision is probably not up to you.

So here is something that you can do: hanging light, gauzy white curtains in front of a southern window will scatter the light in all directions, creating a very even, very pleasant light all over the room (if the curtains are too lacy, i.e. with a bunch of small holes, this will not work as well).  To illustrate, here is the same view again, same time of day, not a cloud between the sun and my window, but with an ordinary white bed sheet tacked up in front of the window:

(I think that is Cleo's ear right there ^ )
Even the ceiling is pretty well lit here.  True, there is still a fair amount of glare by the window itself, but everything else in the room is beautifully even.  This is ideal lighting for most tasks.

The white curtain is a very low tech, very cheap fix for a south facing window.  Closed, it provides privacy and diffuse light.  On a heavily overcast or rainy day you may want to open it, as the curtain does reduce the total amount of light getting in (some is reflected back out the window again).

There are other, more permanent solutions as well (like using frosted glass) but they are mostly more expensive, and as above, not up to an individual tenant or worker.  Also, frosted glass makes a view from the window impossible, while curtains can be drawn back.  But here is one more thing that you can do to maximize daylight in a room with a south facing window:

Hang a mirror on the wall opposite the window.  Courtney and I have used a pattern of mirror tiles, but one large mirror would be even more affective.  This reflects the light that makes it to the far wall back into the room, lighting the other side of objects.  To illustrate, here is an image of a piece of paper held just about a foot away from the mirror:

The top half is catching reflected light from the mirror.  The further from the mirror you are, the lest distinct that line would be, and about three feet away it would be almost indistinguishable.

Using these two techniques in conjunction, the curtain and the mirror, you can get enough light to fill a room evenly and beautifully.  Once the contrast is dealt with, the fact that a southern window gets so much light becomes useful: even a very small window will provide enough light to fill the room most days.


  1. You have two simple yet brilliant ideas here. It isn't always possible to own the place you live in, and when you rent, you don't always have the control to make big changes to the energy consumption of your residence. These two small changes can make a huge difference in the quality of light and therefore the utility of your southern windows in providing adequate daylighting. Two more ideas to throw in the pot - the use of certain paint colors and/or glossy paint can also increase the light reflectance in an otherwise shady part of a room. Additionally, what if you hung mirrors on the ceiling?

  2. Great ideas! I would avoid a high gloss paint on a wall that gets direct sunlight, because of glare, but a "satin" or medium gloss finish will also reflect more than a flat or matte finish. In terms of color, light blue, light yellow and white reflect the most light. Blue will create more cool light, yellow more warm. You could also choose one of these colors for your curtains.

    I don't know about the mirror on the ceiling, it would work for sure, but it just seems odd to me, aesthetically. But, a high gloss ultra bright white or light blue ceiling will do pretty much the same trick.

  3. I like the mirror technique! Unknowingly, I have actually kind of implemented it, as I have two mirrors on the walls that face the windows (they are at different distances from the windows - one on a close wall and one on a far wall). When I was unemployed and home during the day, I found the light to be quite pleasant if I tilted the (cheap, metal, horizontal) blinds at just the right angle. My walls are also a lovely sea foam, and the trim/doors are yellow, which I think helps with the color in the room. It's bright and warm, whereas I think it would feel colder and more glare-y if the walls were white.

    I've been thinking about getting curtains to replace the crappy old blinds some day...good suggestions!

  4. I think that you, like many people, just have a feeling about light. The best choices for good lighting just feel right, even you don't know why.

    I do the blinds thing a lot too, but unfortunately our blinds are kind of a matte white, so they don't get the same reflectiveness. If you can turn the blinds just so, and they bounce a lot of light to the ceiling and don't let in too much direct light, it can have a really great effect.

  5. Oh, also, you can hang a simple curtain rod right over the blinds. Just make sure that the hooks supporting the curtain rod extend past the blinds hardware. That way, if you are renting, you don't have to deal with taking the blinds down, storing, and putting them back up when you move (which also generates some risk of damaging the property).