Christmas house projection: what works, what's hard, and what's still missing

The short answer: to put Christmas lights, snow and characters on your house with a projector, you need three things: a projector bright enough for the wall (about 500 to 1,000 lumens for one window, 3,000 or more for a whole house front), a spot where it fits at the right distance, and a way to make the picture line up with your doors and windows. Kits make the first part easy but play fixed loops in a rectangle. Mapping software fits your house exactly but usually needs a computer. Phone apps are closing that gap, and most of them charge every month.

The ways people do it today

There are five kinds of setup. They differ in what you have to buy, how well the picture fits your house, and what you pay over time.

What makes it hard

1. Brightness

The biggest surprise for most people. A small projector that looks great on a bedroom wall disappears on a house front. Lazy Lighting's guide says outdoor walls need roughly ten times the brightness of indoor surfaces. HeavyM recommends at least 3,000 lumens for a house, and BenQ suggests 4,000 to 5,000. For a single window seen from the street, Easy Mapper says 500 to 1,000 lumens is enough after dark.

Street lights, porch lights and your own Christmas lights all wash the picture out. Turn off what you can near the wall, and judge the result when it's fully dark, not at dusk.

2. Distance and the throw ratio

Every projector has a throw ratio: how far back it must stand for each foot of picture width. A ratio of 1.5 means 1.5 feet back for every foot of width, so a 20-foot-wide house front needs the projector 30 feet away (BenQ explains it here). In a small front yard, that's often the street. Short-throw projectors, usually with a ratio under 1, solve that, and tend to cost more.

3. Making it line up with the house

A projector throws a rectangle. Houses have roofs, gutters, windows and doors. Without mapping, the light spills over everything, and characters walk through the middle of a window. Mapping means telling the software where each shape is, so a wreath sits on the door and snow falls past the windows. On a computer that means tracing every outline by hand; on a phone app you drag corner points over each shape.

Once it's lined up, the projector must not move. A bump, a gust of wind or a tripod leg sinking into wet grass undoes the work. Weigh the stand down, or fix the projector in an enclosure.

4. Windows: the easy, safe place to start

If you want to try this small first, with a projector you already have and nothing left out in the cold, start with a window. Project from inside the house onto a sheet hung behind the glass. Your projector stays indoors, dry and plugged into a normal outlet, and a single window needs far less brightness than a whole house: about 500 to 1,000 lumens is enough after dark, which many home projectors reach (check the lumens in its specs). From the street, the snowman or Santa seems to float in the window. The steps are below.

What doesn't work is shining light straight at bare glass, from inside or out. Glass lets most of the light through and reflects the rest, so the picture looks faint and patchy. It needs something to land on: rear-projection film, or a thin white sheet pulled tight, on the inside of the window. When you're projecting onto the whole house from outside, close the curtains on the windows instead, or cover them with white fabric, so they don't show up as dark holes.

5. Cold, rain and power

Projectors aren't made for winter nights. The projector in AtmosFX's kit, for example, is rated for 32 to 104 °F (0 to 40 °C). Outdoors you need a weatherproof enclosure that still lets the projector breathe, an outdoor-rated extension cord, and a timer so it isn't running at 4 am.

6. Running it every night

If a phone or laptop plays the show, it has to stay plugged in and awake: on an iPhone that means setting Auto-Lock to Never. Kits that play from a USB drive or a small media player avoid this, but can only play what's on them.

The cheapest good start: one window

1. Pick a front window you can see from the street. Hang rear-projection film or a thin white sheet inside it, pulled tight so there are no wrinkles.
2. Put a small projector (500 to 1,000 lumens) on a table inside, behind the sheet, and point it at the sheet.
3. Turn off the lights in that room. Light behind the sheet washes the picture out.
4. Play a slow loop, like falling snow or a figure walking past. Fast scenes are hard to read from across the street.
5. Walk out to the street once it's dark, and adjust from there.

What to weigh before you buy

Whatever you choose, four questions tell the setups apart:

• How long does setup take? An evening of tracing outlines is a lot to repeat every year.
• What does it cost over a few Decembers? Add up the kit, the content and any subscription.
• Does it run by itself? Or does a phone or laptop have to stay awake all night?
• Can you follow the instructions? Some tools assume you already know projector terms.

Before December: a checklist

• Measure the width you want to light and where the projector can stand. Check it with the calculator above.
• Choose brightness for the surface: about 500 to 1,000 lumens for a window, 3,000 or more for a house front.
• Get a weatherproof enclosure, an outdoor extension cord and a plug-in timer for outdoor setups.
• Cover or curtain the windows you're projecting over.
• Test on a dark night a week before you want it up, and look from the street.

Sources

• AtmosFX: AtmosKIT HD Christmas
• AtmosFX: illumibot projection mapping kit
• HeavyM: how to do house projection mapping
• BenQ: complete cost breakdown for house projection mapping
• BenQ: what is throw ratio
• BenQ: house mapping tutorial for beginners
• Lazy Lighting: projection mapping app
• Easy Mapper: window projection app