One of the most frequent concerns addressed in advertising for new construction or renovation is the abundance of natural light. Large windows are ubiquitously advertised and unquestioningly desired. While natural light is good for your health and aesthetically pleasing, some questions should be asked about the large-window craze.

The first question to ask is why we feel the need for great large windows. Presumptively, it feels dark. But is it dark? Or what causes the sensation of darkness? Every day at work in the morning I’m supposed to update a series of numbers on a large whiteboard. If I don’t get them all done before the meeting begins, I finish up in the second half of the meeting when they turn on a projector and turn off the lights. As I am standing there writing on the board someone flips the switch, and it becomes too dark to write. Yet it brightens back up, without anyone turning on any lights; my eyes adjust to a new threshold of ambient light, and it no longer seems too dark to write.

That example is a little trite. We all know about our eyes adjusting to darkness. But similar effects apply in more nuanced situations. In my apartment kitchen, there’s a window and door with a glass pane on the same wall. When I first arrived, I felt that the side of the kitchen where I put my table was hopelessly dark, and I figured I would probably have to buy a lamp, even though there was a set of florescent bulbs installed in the ceiling, or do something else to relieve the darkness. I planned to hang a mirror on the wall, a larger mirror I picked up for free; but it desperately needed to be refinished and I procrastinated at that.

It happened that before I got around to addressing the darkness of that corner, I got a curtain for the glass in the door for privacy’s sake. After that I did not feel the need for lighting the table end of the room so much. I did not notice any dramatic difference, but the sense of gloom on that side of the room abated.

There are two possible effects at work. First, the curtain diffuses the light, scattering it into the room in more directions than it would stream in through clear glass. Second, by dimming and diffusing the sunlight as it enters the room, it reduces the impact of the direct sunlight and lowers the threshold of lightness, like turning off the lights in the meeting, so that the somewhat dimmer side of the room does not contrast as sharply with the light beaming in from outside. Opening up the blinds over the window somewhat negates this effect, letting stark daylight into the far end of the room (although with the door still shaded and with greater space between the extremes of light, the contrast is not as severe as it was). Thus, while I occasionally open the blinds to enjoy a full blast of daylight, keeping all the windows at least partly shaded gives a brighter overall feeling to the room. The light does not simply seem brighter; I always know that there is brighter light being obscured. But sharp, strong light creates a sense of urgency, where diffused light allows more relaxation and does not make you feel like you must choose between being in the light and in the dark.

The house I grew up in was built long before wiring was common, and retrofitted with an outlet per room. Lighting was in short supply. Also, with a steadily rising number of kids, none of whom respected the niceties of things, lampshades fell victim to intentional and collateral damage. So we wound up with a lot of bare bulbs trying desperately to light rooms by their own strength. Over the years wiring was upgraded and added, so higher wattage bulbs were used and gradually more were available for service. Yet I’ve noticed that no matter how many watts of illumination there are, you can still feel like the room is too dark. I think that’s not really darkness per se, but the harshness of the light. In fact, when some of those stick-on LEDs were purchased to light a dark corner, people complained they were too harsh and made the area feel darker.

The psychology of light and dark goes beyond the actual amount of light, beyond even contrasting levels of light. I have noticed that I feel the need for light more urgently when there is clutter, while dimness is more acceptable when things are neat. A bunch of clutter under strong light looks like work in progress, while a bunch of clutter in the dark looks like forgotten junk. So simply shining brighter light on something that needs to be taken care of may help us feel like something is being done about it.

Another thing to consider before building a glass wall is what you are going to do on the interior side of the wall. I am always going to want more window space in my living room than in my bedroom, yet I like a window even in the bathroom where privacy is a top priority. The size and proportions of a room will affect the size of the appropriate windows. But there are some things I think are extreme no matter what room of the house you are considering. There’s a style of “log” house that makes one gable-end wall of the house nearly all glass, right up to the peak. I don’t want that much glass in any room of my house. In the lobby of a public building such glazed vistas may find their place, but I want my house to feel like a home and to have a protective presence around me. When I want to be wide open to the outdoors, I’ll go outdoors. That’s another thing I think feeds the craze for plenteous glass. We are spending more and more time indoors, in front of electronic devices and surrounded by air that’s neither too cold nor too hot, and we find ourselves lacking in exposure to the outdoors. But windows don’t really remedy that. To enjoy nature you need to be out in it, simply observing it through glass is not a whole lot better than watching the nature channel on TV. Attempting to compensate for a secluded life by putting in big windows I think is a antidote without lasting effect.

Personal preference will still play a role in how much glass is satisfactory. I think, though, that many of the people who want “lots of natural light” in their homes will find the bedroom better served by modestly sized windows on two or three walls rather than a wall of glass; or they may find that generous light in the living room and kitchen leaves them perfectly happy with fewer and smaller windows in their bedroom. Contrast and context are extremely important in our appreciation of light, and without adapting to these variables we can find ourselves going from “too dark and claustrophobic” to “overexposed and out of place” without attaining the sense of comfort we were looking for.