Methodology & limits

What “Beta” means

Roomlit is a test version. It is free, it still changes, and its results are estimates. We have not yet compared them with measurements in real apartments. Use them to compare apartments and to know what to look for on a visit, not as a promise.

How it works

1. Find the address. We look up the address you type and get its location on the map.
2. Load the buildings nearby. We load the outlines and heights of buildings within about 1,000 ft (300 m). You then choose your building and the side of the building your main windows face.
3. Read the floor plan. An AI service reads the walls, rooms and windows from the floor plan you upload. You check and correct it on a drawing. Without a floor plan you can use a simple room (one rectangle), or only the side of the building.
4. Trace the sun. For the address and the date, we work out where the sun is in the sky every 15 minutes from sunrise to sunset. For each time, we trace straight lines from the sun through your windows and check whether a nearby building is in the way. Where the sun gets through, we mark the patch of floor it lights. You can pick any date, or one of four typical days: June solstice (Jun 21), December solstice (Dec 21), March equinox (Mar 20) and September equinox (Sep 22).
5. Walk through. With a checked floor plan, you can walk through a 3D model of the apartment and see the sun patches at any time of the day.

Where the data comes from

• Address search: Photon (by komoot, based on OpenStreetMap) while you type. When you pick one of its suggestions, we use the location Photon gives for it. Only when you choose “Search for what you typed” do we ask the US Census address lookup service (a US government service) instead. Either location can be on the street rather than on the building, so you choose your building on the map yourself.
• Buildings: Overture Maps building data (our own copy for Houston). Outside that area we use OpenStreetMap through the Overpass service (© OpenStreetMap contributors).
• Building heights: from the map data where it has them. Many buildings have no height in the data; then we estimate it from the number of floors, or from nearby buildings. The app says how many heights were estimated.
• Sun position: calculated with standard astronomy formulas for the exact place and date.
• Floor plan: the image you upload, read by an AI service and checked by you.
• Map pictures: Stadia Maps. They are only a background; nothing is measured from them.

We do not use these Google services anywhere: Google Maps, Google Photorealistic 3D Tiles, Google Solar API (a Google data service about sun on roofs).

What we assume

• Every day is a clear day: no clouds, no rain, no haze.
• Each floor is 10.5 ft (3.2 m) tall, and floor 1 is at ground level, unless you tell us otherwise.
• Window bottom (sill) and window top heights are typical values for the type of building when the floor plan does not show them. We show a range when they are not known.
• Buildings are simple blocks: no balconies on other buildings and no roof shapes.
• Trees: on the Sunlight page, trees never block the sun, because we do not know if they have leaves (the tree setting “Trees not counted (as on Sunlight)”). On the Compare page you can choose another tree setting. Most maps have no tree data, so the setting often changes nothing.
• Times are Houston time — Central Daylight Time (CDT) in summer, Central Standard Time (CST) in winter.

How accurate it is

Not checked yet. We have not compared the results with measurements in real apartments. These are the goals we want to reach and test:

• Say correctly whether a window gets direct sun at least 90% of the time (goal, not yet checked).
• Start and end times of direct sun within about 30 minutes (goal, not yet checked).
• How far the sun reaches into the room within about 20% or 0.5 m (1.6 ft) (goal, not yet checked).

The biggest sources of error are wrong building heights, the wrong side of the building, and wrong window heights. Each result lists what it assumed, so you can check these.

What is left out

• Weather and clouds. Every day is treated as a clear day, so real days can have less sun.
• Indoor temperature, heat and energy bills. We do not model heat.
• Brightness in lux (the unit a light meter shows). We do show a relative daylight grade for each room (Low, Medium or High) and how strong the direct sun is compared with other times, but no lux values.
• Reflections. Sun bouncing off glass on other buildings is not included.
• Public sharing. Signing in only copies your own apartments to your other devices; there are no public links. Paying only buys more AI floor-plan readings; it never unlocks extra results.
• Checks against real measurements. We have not yet compared the results with measurements in real apartments.

More

Privacy explains what data goes where. Terms covers the beta rules and what credits buy.