Light That Travels: Why the Window Between Your Rooms Deserves Another Look

There is a particular sort of window in a British house that never sees weather. It doesn't face a street, a garden or a view of next door's extension. It faces the landing. Or the hall. Or the back of a cupboard someone built in 1987 and never quite finished.

You probably walk past three of them a day without registering that they're there — or, more likely, you register them only as that draughty panel above the bathroom door or the thing the previous owners covered with a roller blind that has since gone the colour of milky tea.

They're worth a second look. Not because they're rare or grand, but because they do something almost no other feature in a house can do: they move daylight from where it is to where it isn't.

The opening that isn't quite a window

A quick bit of vocabulary, because these things get lumped together and they're not identical.

A fanlight is the glazed panel above a door, traditionally semicircular in Georgian and Regency houses, though plenty of Victorian terraces have a plain rectangular one. A transom light or overdoor panel is the horizontal glazed strip above an internal door — very common in hallways of 1890s–1930s homes, and frequently the first thing to be blocked when someone fits a cheap blind. An internal window is the standalone one: a framed opening set into a partition wall between two rooms, sometimes with a little sill, occasionally with a decorative leaded pattern that suggests the builder was showing off.

There are cousins, too. Glazed panels either side of the front door. The glass above a stairwell. The serving hatch that someone's grandmother used to pass plates through, which is technically a hole but behaves like a window if you let it.

All of them run on the same principle, and it's an old one: borrowed light.

Why borrowed light changes how a room feels

A room lit from one direction only reads as flat. Corners go muddy, the ceiling loses its shape, and anything with a bit of texture — cornice, picture rail, panelling — quietly disappears after about 3pm in November.

Add a second, weaker source of daylight and all of that softens. It doesn't make the room brighter in any measurable sense; it makes it feel less enclosed. A hall stops behaving like a corridor and starts behaving like a room. A landing stops feeling like the place where the boiler lives. A dark middle room in a terrace — the one that gets nothing but a borrowed glow from the front room — suddenly has depth.

This is why people instinctively put mirrors in hallways. An internal window does the same job, but with actual light and a fraction of the fuss.

Read what you've actually got before you touch it

Before the ideas, a bit of honest assessment. Internal glazing is old, and old things have opinions.

Is it painted shut? Very often, yes. Decades of gloss on the frame and the sash will have welded it into the wall. That's not necessarily a problem if you only want to see through it, but worth knowing if you were hoping it opened.

Is the glass original? Wavy, slightly bubbly glass with a faint green cast is probably Victorian or Edwardian, and worth keeping for the texture alone. Textured, reeded or patterned glass is usually a deliberate privacy choice — someone thought about this once, which is more than can be said for the blind.

Is it condensing? Consistent misting between panes suggests a failed seal on a modern unit, which is a replacement job. Condensation on the room side is just a ventilation and warmth conversation, and a much easier one.

Is the door it sits in a fire door? This matters. Glazing in fire doors — particularly the door between a house and an integral garage, or in a flat conversion — is there for a reason and shouldn't be swapped for ordinary glass, covered permanently or removed. In an ordinary internal door in an ordinary house, you're fine. If in doubt, leave it and ask.

And one more: if the paint looks thick and has that faintly chalky alligator texture of old layers, don't start sanding without thinking about lead. A test kit costs less than a takeaway.

The privacy question, answered honestly

Here's where most people stall, and rightly. A window between a bathroom and a landing is not a character feature; it's a design fault with a frame around it.

But total opacity is rarely the only solution. The trick is to think in terms of how much rather than whether.

• Frosted or reeded film. Cheap, removable, and far better looking than it used to be. Reeded effect film in particular reads as a period choice rather than a compromise, and it lets a surprising amount of light through.
• A café curtain on a tension rod. No drilling, no brackets, no builder. A half-drop of washed linen or a simple cottonvoile covers the sightline without killing the glow. Works beautifully on a transom above a bathroom door.
• A lined Roman blind on a batten. Mounted inside the reveal rather than over the face of the frame, so the architrave stays visible — which is the whole point. Line it, and it'll do some draught duty as well.
• Shutters, half-height. Louvre panels in the lower half only, so light still spills over the top. More expensive, but it's the version you'll still like in ten years.
• Something staggered in front of it. A slim shelf of plants, a row of books with gaps, a collection of small ceramics on the sill. Anything with gaps lets light through and gives you a reason to look at the opening rather than past it.

What doesn't work: a roller blind pulled down permanently, or a sheet of MDF and a coat of paint. Both are the reason the window is currently dead, and neither is a fix.

Holding on to the warmth

An internal window doesn't leak heat to the outdoors — that's the good news. The bad news is it does let warm air drift from a heated room into a cooler landing, and single glazing feels cold to sit beside.

For a low-cost holding pattern: shrink-fit secondary glazing film on the room side is genuinely effective and completely reversible. A lined blind drawn at dusk does more than most people expect. A heavy curtain on a slim blackened-metal pole, hung high and wide, adds softness and stops the draught without hiding the frame. If the glazing is beyond saving and you're replacing it, a slim-profile double-glazed unit in a timber frame will look far more at home in a period wall than uPVC — and nobody will ever know from the street.

Sometimes the answer is nothing at all

Before you buy anything, spend one evening with the covering taken down.

Really. Take off the blind. Pull out the four hundred tiny brass pins holding the old net curtain. Clean the glass with a bit of warm water and a drop of washing-up liquid, and see what the room does at 5pm.

Frequently, the answer is: it's fine. Nobody can see in. The landing is transformed. The hall has a bit of life in it. The only thing standing between you and a better house was a blind nobody liked and a hook nobody removed.

Then, if privacy really is a problem, dress it properly. But do it knowing what you're covering, and why — because a borrowed-light window is one of the few character details a UK home gets for free, and it's a shame to spend another winter with it switched off.