Control lamp light by covering every window after dark with overlapping heavy cloth hung so that it can be pulled down from inside in the dark in one movement, using only rooms without outside windows for light, and baffling any vent so air still flows. Never nail, screw or wedge a covering over an opening someone may need to climb out of.
Part of Camouflage and Concealment
Artificial light control is the practice of stopping lamp, candle and stove light from leaking out of a building at night while keeping its windows usable as exits and its air supply open.
A Blackout Is Also A Blocked Window
The parent article gives the blackout rule: cover all windows after dark with heavy cloth, cardboard or tarps, because even a small gap leaks light that can be seen at distance. It adds the safety rule that matters here: cover windows you may need to climb out of with something you can pull down from inside in the dark in one movement, such as a hanging cloth or a propped panel, never a sheet nailed or screwed over the opening. A blacked-out window is also a blocked escape opening, and a fire at night is the situation in which both facts apply at once.
Everything below is designed around that rule. The covering is a removable part of the window, not a permanent change to it.
What You Need
- Heavy cloth, blankets or hides — thick enough that a lamp held behind it is not seen from a metre away
- Hooks, nails driven into the frame above the window, or a curtain rod — something to hang the cloth from; hang it, do not fasten it down
- Cleats or a shelf — if you prefer a rigid panel, rest it on cleats so it lifts off
- A ventilation baffle — an offset board or bent tube that lets air in and not light
- A shielded lamp kept by the bed — for the moment the cover comes down
Method: Hang, Overlap, Test, Rehearse
Step 1: Cut the cover larger than the opening. Overlap the frame by about 10 cm each side so light does not escape round the edges. For a window 60 cm wide and 90 cm high the cover is 60 + 2 × 10 = 80 cm wide and 90 + 2 × 10 = 110 cm high. The overlap is a design choice for the example, not a measured standard.
Step 2: Hang it from the top only. Use hooks or loops so that one tug on the bottom edge brings the whole cover down. Panels stand on cleats and lift away. Nothing is nailed through the cloth into the frame, and nothing sits across the opening below the cloth.
Step 3: Make rooms with no outside windows your light rooms. The parent article suggests halls and closets, and rooms with windows that are fully covered. Keep lamps low and away from the cloth, which can scorch.
Step 4: Test from outside. After dark, walk round. Look for light at the edges of the cloth, under doors and through gaps in shutters. Fix leaks and check again.
Step 5: Baffle vents. A vent that lets in air also lets out light. Fit an offset or S-shaped baffle: air bends round it, light travelling in a straight line does not. Do not close vents altogether when a stove or lamp is burning.
Step 6: Rehearse the exit. Tell everyone in the house which windows are exits. Once, in the dark, have each person pull down the cover and get out. If anyone cannot do it, the covering is wrong.
Common Mistakes
- Using a nailed sheet because it is quick. It is quick to put up and impossible to remove in a fire.
- Light from the door. Opening a door to a lit room throws light across the yard; use a porch or a second blackout curtain as an air lock.
- No one told about the exits. Visitors, children and the elderly need to know which window comes down.
- Cloth over the lamp. The parent article says to use red filters for torches; do not cover a flame with cloth, which burns.
Safety
Fire, carbon monoxide and a blocked exit
A fully blacked-out room with a lamp, candle or stove burning can fill with carbon monoxide and run short of air; see Carbon Monoxide Risks and keep a baffled air inlet and outlet open. Hung cloth near a flame can catch fire; keep lamps on a fireproof surface well away from cloth, as in Lamp Fire Prevention. Never fasten any covering over a window or door that is an exit. If a covering cannot be brought down by a child in the dark, replace it.
What’s Next
- Learn next: Reflective Surface Management — glass and metal that give you away in daylight
- Combine with: Window Design — how the window itself is built and what covers it