I Can See Clearly Now: Daylighting II

Want to see how the light will look before you spend money on remodeling windows, adding skylights, or repainting a room? If the answer is yes, have I got a story for you!

RoomBefore
The room has a nice warm quality when lit with two different sources of artificial light. This is at 4:30 on a summer afternoon. (Note the yellow wood stairs that cover and shade much of the left side of the south-facing window.)

RoomDark
Here's how it looks at noon with the lights off. OK for computer work, but it's hard to read a book. Light comes from the south-facing window and an east-facing door that leads to the kitchen and living room.

I recently built a scale model of my dining room and tested eight ways to increase the room’s natural light. My tests yielded some surprises – insights that I will share in this post.

As you can see from my photos, it’s so dark that, without artificial light, the pink walls in my dining room/office look smoky gray. When the room was occupied only at night, this wasn’t much of a problem. However, as I have moved my design practice into the room, the lack of natural light has become an issue. There are multiple reasons for that:

  • Human beings need full spectrum light for accurate color perception – a fact that makes natural light particularly important for visual designers.
  • Humans also perform better in natural light. Studies show that adequate daylighting can increase building lease rates, reduce worker absenteeism and sick leave, increase production, result in higher sales, and speed patient recovery times in hospitals. It has even been shown to help raise student test scores and reduce tooth decay.
  • Lack of natural light can impact mood. Like many other people, I suffer from SADS, or Seasonal Affective Disorder Syndrome, and natural light helps combat these blues.
  • We waste a shocking amount of electricity lighting our buildings during hours when sunlight is readily available. I find this reprehensible for both environmental and economic reasons.

Regular readers of this blog may recall that I wrote about the first version of this model in A Light at the End of the Tunnel, Daylighting. That post contains much more information about the health and energy benefits of daylighting, as well as summaries of some daylighting strategies that I decided not to test on my model. For that reason, I don’t talk about them here, but you might find them of interest if you’re trying to lighten up your own dark room.

Match Wits with My Model

Before I share the results of my experiments with the daylighting model, I invite you to test your best guesses about what would most help to lighten the room.

Below, I have listed, in alphabetical order, the eight alterations I made to the model, giving each a two-letter mnemonic code. Take a moment to rank these options so that you can compare your predictions with the results of my experiments. (Put the number and code for the strategy you think would make the most difference first, the second-most effective strategy second, and continue until you have ranked all eight alterations in order of expected effectiveness.) You may be as surprised as I was by what worked, and what didn’t add much light to the room.

Here's where the window and stairs are located on the actual house.
Here's where the window and stairs are on my house.

Here are the alterations I tested:

  1. AW – All white – Painting the entire dining room white
  2. CL – Clerestory windows. Cutting clerestory windows through the east wall of the room to admit more light from the living room (wide, short windows located up near the roof where you can’t see through them are called “clear story” windows)
  3. MI – Mirror inside. Mounting a mirror on the sunny, west wall within the room
  4. MO – Mirror outside. Mounting a mirror on the outside wall that reflects the most light in through the window
  5. OS – Open Stairs. Replacing the solid wood stairs with openwork metal stairs that allow light to shine through
  6. WE – Window Extension. Extending the dining room window up to the ceiling
  7. WI -White inside wall. Painting the sunniest wall, the one that reflects the most light inside the room – white instead of pink
  8. WS – White stairs and stairwell. Painting the outside stairs and stairwell white, leaving the room pink

My test results will be revealed at the end of this blog. In the meantime, here’s a bit more information about the model, and some photos of the changes in light produced by various alterations.

The Second Daylight Model

Model
The daylight model; this is the same side of the house that is shown in the photo above.

To make the light in my daylighting model accurately show the changes I wanted to test, I expanded my original one-room model so that it would show both the main sources of light and the features that obstruct it. The expanded test model, the second daylight model, is shown at right. It includes:

  • Yellow painted stairs that block much of window – they can be seen on the left side of the model and also in the dark photo at the top of this post.
  • Door to kitchen – the door is at the center of the model. Here the kitchen is represented only by the tile placed outside the model. This is the same tile that is installed in the real kitchen, and it reflects a surprising amount of light.
  • Living room – the space to the left of the door is the dining room. The main sources of living room light are the  window at the right side of the model and the door into the kitchen. Light from the living room enters the dining room through the door on its east side.

Mirror, Mirror on the Wall?

Adding a mirror inside the room reflects light, but not as much as I expected.
Adding a mirror inside the room reflects light, but not as much as I expected.

Here's a surprise - look at how much more light the room gets when the mirror is placed OUTSIDE on the landing!
Here's a surprise - look at how much more light the room gets when the mirror is placed OUTSIDE on the landing!

YellowWhiteLanding
Painting the wall outside the window white reflects about the same amount of light as a mirror in the same spot.

A white wall, white stairs and whitewashing the black tar roof (unseen from this angle) reflects the most light of any of these options.
A white wall, white stairs and whitewashing the black tar roof (unseen from this angle) reflects the most light of any of these options.

At the outset, I thought that placing a mirror to catch and reflect sunlight falling on the room’s west wall (right side of the photo) would brighten the room a great deal. One of my fellow designers suggested this idea, and I was eager to try it.

The prof in my Building Envelope class, however, was unenthusiastic. He noted, rather disdainfully, that this smoke-and-mirrors trick would make my room look like every third restaurant in downtown San Francisco!

I was surprised to discover that placing a mirror outside the window – as the photo at far right shows – brightened the room far more than a mirror inside the window.

What startled me even more, however, was the discovery that white painted walls, both inside and outside the window, reflected more light than mirrors in either position! This seemed counter-intuitive, but both experiments with the model and a review of ASHRAE tables confirm it.

ASHRAE is the acronym for the American Society of Heating, Refrigerating and Air Conditioning Engineers, and they have published extensive tables that list the reflectance of dozens of types of building materials and finishes. The reflectance standard for a perfect mirror is 100% (meaning that it reflects all of the available light) and is referenced as a value of 1.0. The aluminum foil I used in the model as a “mirror” is not perfect, but polished aluminum has a reflectance – or “R value” – of .8 to .9, and many mirrors are actually in that range too. So the foil probably gives us a good idea of how much light a real mirror would reflect.

A white masonry wall, according to the ASHRAE charts, also has an R-value in the range of .8 and should reflect about as well as the mirror. My model experiment not only confirms this, it also reveals that the reflectivity from white walls provides a much more even wash of light than the mirrors do. Look carefully at the light on the floor and ceilings in third photo at right and you will see this. In addition, you will see that the painted wall actually reflects light back into the depths of the room better than any of the mirrored options.

The fourth photo in this series shows that the room is significantly brightened when the outside wall, the bottom of the staircase, and the black tar roof outside the window (unseen in the photos here, but visible in the model above) are all painted white. The amount of light reflected onto the ceiling is substantially greater than in any of the preceding photos, and the wash of light to the right of the window reaches deeply into the room.

More Light from the Adjacent Room?

Clerestory windows were invented to let light into Gothic churches on the level above the stained glass windows that line the nave, and today, clerestory windows are often used in green buildings because they offer a great way to get to light travel from perimeter rooms into windowless interiors.

ClerestoryAs you can see from the photos in this post, my room receives a lot of light from the east wall’s door that opens to the living room and kitchen. I had hoped that installing clerestory windows in that same wall would add light to my dark dining room – but it was definitely an option I would want to test before trying it in real life. While it was easy to add the little windows shown at left to my model, adding them to the house might be quite an expensive option. To add them, my contractor would need to pierce a load-bearing wall that provides support to the building’s upper floor. That’s not impossible, but it would necessitate reinforcing the wall, and that would add to the cost of the project. Unless the clerestory windows added a lot of light to the room, they wouldn’t be worth the expenditure.

That’s exactly what the model showed. The amount of light the clerestory windows added to the room was negligible – much less of an improvement than I would get from simply painting the east interior wall of the room a lighter color! (You can see the model’s clerestory windows in the photo at the bottom of this post.) So that’s a neat $5000 or so the model has saved me. Painting all of the walls white of course increased this effect.

Buying a Stairway to Heaven

StairsOldNew
The old, solid wood stairs at left. New, pierced metal version at right.

The most obvious barrier to daylighting in this room, of course, is those darn stairs. They not only block the view, but they also shade the window from the wonderful south light that comes into the kitchen and living room, and from light that would fall from the sky directly above the stairs.

Those stairs need to be rebuilt, and I have wondered whether leaving the risers open at the back of the stairs (or alternatively, putting a transparent material at the back of the riser) would significantly lighten the room.  Ryan Stroupe, from whom I was taking a green building course, suggested something even better: what if the stairs were made from a pierced or open metal grating? I tested that option by building a set of stairs for the model out of metal window screen; you can see the old and new stairs in the model photos above.

FullMonty
Here's the model after all eight alterations have been made. The best improvements came from painting the light well's surfaces white, raising the top of the window, exchanging the solid wood stairs for metal stairs that admit light, and painting the interior walls white. You can see that the clerestory windows, at top left side, don't add much light to the room.

My last change was to further open the room by extending the room’s window up as far as possible toward the ceiling. Obviously, this strategy would work best with open stairs and an open top landing.

Grand Finale

Drumroll, please! After all this testing and photo-taking, I can clearly see what’s going to work best, and you can compare your predictions to the results. Here’s how the eight possible improvements stacked up:

  1. Open Stairs
  2. Window Extension
  3. White stairs and stairwell
  4. White outside wall
  5. Mirror outside
  6. White inside wall
  7. Mirror inside wall
  8. Clerestory windows

Interesting, eh? How well did your predictions turn out?

If you’re thinking about improving the daylight in a room, here are some resources that you might find useful:

>>>>>>>>>>>>>>>>

NicoLadder

I Can See Clearly Now

I can see clearly now, the rain is gone,
I can see all obstacles in my way
Gone are the dark clouds that had me blind
It’s gonna be a bright (bright), bright (bright)
Sun-Shiny day.

I think I can make it now, the pain is gone
All of the bad feelings have disappeared
Here is the rainbow I’ve been prayin’ for
It’s gonna be a bright (bright), bright (bright)
Sun-Shiny day.

-Johnny Nash

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2 thoughts on “I Can See Clearly Now: Daylighting II

  1. I’m coming late, but we have the same issue – actually, different in the way of reducing all openings to the minimum possible, AND gaining light inside.

    The item that makes the biggest difference of all is the sheen of the paint.
    We have a lightwell painted white bluish in sateen paint – and it brings more light than I need. I’ll tone down the color next painting.
    All our inside ceilings are sateen (just shy of semi gloss). From one small window, the whole ceiling GLOWS natural light. (walls are also sateen, but with saturated victorian colors). It also lets you light a 15×14 room with a mere 3 x 15watts CFL fixture.
    Avoiding any @#$^!#$^! paint called “ceiling” is the first step to sanity. Those paints are powdery, dirty white and swallow light nearly as well as a black hole.

    You also need to have a clean sateen finish on your wood floors.

    so in short: sateen finish on all surfaces: floor, ceiling, and walls. Semi gloss on trims.

    As for colors, beware of too much white. An all white room is much smaller than well defined surfaces, and white bounces the light without direction – which is a problem, because a well designed room has only light from above and from one source on one side. Otherwise your brain gets confused and you might have the opposite of SADS – which was pretty horrible in our house and made me close all the curtains all the time.

    One of your neighbors

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