Light
A mirror is a light fitting that runs on the window
Mirrors do not create light, but placed correctly they extend the reach of daylight and double the apparent depth of a room. Placed badly they reflect a wall.
Everything below about mirrors and daylight comes from what actually happens rather than from what is supposed to.
What holds up in practice
- A mirror reflects whatever is opposite it, so the view it doubles is chosen by its position.
- Reflected daylight falls off with distance like any other light source.
- A mirror facing a window sends much of the light straight back outside.
What a mirror actually does
A mirror returns the light that reaches it, so it can redirect daylight into a part of a room the window does not reach directly. It also presents a reflected image of whatever sits opposite, which is why a mirror facing a blank wall makes a room feel larger by exactly nothing.
The apparent depth it adds is real to the eye, because the reflection recedes and the brain reads it as continued space. Total light in the room barely changes, since a mirror cannot generate anything, and some light is absorbed at every reflection. What changes is where the light lands and how far into the room the eye can see, and both of those alter how bright a space feels.
Position decides everything
A mirror on the wall adjacent to a window catches daylight at an angle and throws it deeper into the room. A mirror directly opposite a window returns a good deal of that light back towards the glass, which wastes much of the opportunity.
Placing a mirror where it reflects a doorway or a view through to another room extends the sightline and reads as more space. Reflecting something worth looking at, a green outside, a bookcase, a lit corner, gives the eye information rather than a repeat of the same wall. The reliable method is to hold a mirror up and walk it around the room, because the correct position is usually not the obvious one.
Size, height and shape
A large mirror behaves like a window in the composition of a wall, while a small one behaves like a picture. Mirrors hung too high reflect the ceiling and the tops of heads, which is a common fault in hallways and above fireplaces. A tall mirror reaching close to the floor reflects floor surface, which is the trick that makes a narrow hallway read as wider.
Leaning a large mirror against a wall tilts it slightly downward, changing what it reflects and often improving it. Anything large and heavy needs fixing into something structural, and a leaning mirror in a house with children needs securing regardless.
Mirrors and artificial light
A mirror behind a lamp or a candle doubles the visible source, which is why the effect reads as warmth rather than as brightness. Placed opposite a bright fitting, a mirror puts a glare source into the field of view from seats that previously had none. In a bathroom the mirror is the working surface for the light, and side lighting at face height is what removes shadows.
Underneath it, overhead light in front of a mirror produces exactly the shadows people complain about while shaving or applying make-up.
A mirror can also be used to bounce a lamp indirectly, which softens the light in the same way as aiming it at a pale wall.
The kinds of mirror and how they age
Modern mirrors are float glass with a metallic coating and a protective backing, and they fail from the edges inward where moisture reaches the coating. That is why bathroom mirrors develop dark speckling at the edges, and why a sealed edge or a mirror intended for wet rooms lasts longer.
Antique mirrors were silvered differently and their patchy backing is part of the character, though the reflection they give is dimmer. Antiqued and smoked glass reduces reflectivity deliberately, which trades usable light for a softer effect. Cleaning with anything that runs to the edge shortens a mirror life, because the liquid enters behind the coating.
Taste is not the argument here; how a room performs is.
Where mirrors are the wrong answer
A room lined with mirrors becomes disorienting rather than spacious, because the eye loses the boundaries of the space. Mirrors opposite each other create an infinite corridor that most people find uncomfortable to sit in. A mirror where it reflects a bed or a doorway can be unsettling at night, and cultural attitudes to this vary considerably.
Live with it a while and in a room with almost no daylight, a mirror has little to redistribute, so the gain is visual depth rather than brightness. The honest question is what the mirror will reflect for the hours the room is used, and whether that is worth looking at.
The takeaway
Hold it up and walk it round the room, because the right wall is the one that reflects something worth seeing.
Buy slowly. The gaps are not a problem.
Questions readers ask
Where should I hang a mirror to brighten a dark room?
On a wall adjacent to the window rather than opposite it, so it catches daylight at an angle and pushes it into the room instead of returning it to the glass.
Do mirrors really make a room look bigger?
They add apparent depth by reflecting space the eye reads as continuing. That only works if what they reflect is space rather than a blank wall.
