Lights Down — what movie do we watch?Pick tonight's movie →

How Lights Down works: where the movies, ratings and streaming data come from

Lights Down asks TMDB which movies stream on the services you have in your country tonight, learns what your group feels like from a few quick this-or-that picks, and ranks the list by fit and rating. This page explains where every fact comes from, how the ranking is computed, and what the tool cannot know.

Where the data comes from

Movies, ratings and posters: TMDB (The Movie Database), a community-built database, through its API: titles, release dates, runtimes, genres, keywords, directors and cast, age certifications per country, the average member rating and the number of votes, and poster images from TMDB's image servers. This product uses the TMDB API but is not endorsed or certified by TMDB.
Where to watch: TMDB's watch-provider data, which comes from JustWatch: for each movie and country, which services carry it on a subscription, for free, free with ads, to rent or to buy. Every where-to-watch box links to the full live list. Availability changes daily; the app always shows when its data was fetched.
What you have already seen (optional): If you add Letterboxd usernames, each member's public RSS diary feed — the path Letterboxd itself points developers to; its API is not open to projects like this. The feed carries the latest diary entries (about 50): film, year, star rating, the date watched and whether it was a rewatch. Diary data from Letterboxd RSS; not affiliated with Letterboxd.
"Ends by": Your device's clock plus the movie's runtime from TMDB (plus 20 minutes when you switch on "+ trailers"). Nothing is sent anywhere to work it out.

What the app asks for

When you press Go, the server asks TMDB's discover search for movies available in your country on the services you ticked (subscription, free or free with ads), with at least 30 votes, shorter than your time minus ten minutes, most popular first — up to 60 at a time — and fetches each movie's details and where-to-watch list. Answers are cached on the server: discover searches for 6 hours, movie details and availability for 24 hours, the list of services, countries and genres for 7 days, Letterboxd feeds for 20 minutes. The cache is keyed by the question (services, country, length), never by who asked.

How the picks are weighted

This or That deals each person twelve pairs of well-known posters, chosen to differ as much as possible (no shared genre, different decades). Every pick adds weight to the winner's genres (+1), keywords (+½), decade (+½) and length band (+½) and subtracts the same from the loser's; skipping is allowed. Films someone rated four stars or more on Letterboxd count as a small head start.

Merging. For every genre, keyword, decade and length band, each person's weight becomes an affinity between 0 and 1 (half means no opinion), and the group's affinity is the geometric mean of everyone's. A geometric mean is dragged toward zero by any single zero, so one person's hard no works as a veto instead of being outvoted — a movie only ranks high when nobody in the room hates what it is.

Tonight scores every movie as fit × quality × recency. Fit is the cosine similarity between the movie's features and the merged taste, stretched to 0–100% with 50% meaning neutral (every movie gets 30% before anyone has picked). Quality is (TMDB average ÷ 10)², damped when few people voted (× log₁₀(votes) ÷ 4, capped at 1). Recency adds up to 8% for releases from the last eight years. The roll draws at random with odds proportional to the score squared; the first roll of a session comes from the top four. Films either of you logged on Letterboxd in the last 90 days are hidden unless you switch that off.

Bracket seeds the same ranking (1 vs 8, 2 vs 7 …) and pairs first-round opponents of the same genre where possible, finer pairings in bigger brackets. Find New keeps "hidden gems" — rated 7 or higher by 300 to 3,000 TMDB members — that fit your picks at least as well as the median, and names the genres and keywords that matched.

Tonight's lists and movie pages

The lists (comedies under 100 minutes, 80s movies, movies for a group …) are built live from TMDB for the United States: movies streaming on a subscription or free service, with at least 300 votes, most-voted first. Every movie has a page with its runtime, rating, certification, a "good for a group?" verdict and where it streams in your country (loaded live when you open it). The 2,000 movies with the most TMDB votes are offered to search engines; the rest stay reachable but unindexed.

What it cannot know

No streaming service shares what you have watched, so without Letterboxd the app cannot hide films you have seen — veto them instead. The Letterboxd feed only reaches back about 50 entries, so "hasn't logged it" means "not in their latest entries". Availability can lag a day behind the services, and a movie can leave a service after you pick it. Ratings are TMDB members' ratings, not critics'. Certifications are missing for some countries, in which case the US rating or none is shown. If something is wrong, TMDB is the place to fix it: corrections there reach this site within a day.

By genre and length

By decade

For the occasion

Who makes it

Lights Down is a program from Somebody Decide, a small software studio operated by RapidShift, LLC. Small free programs that settle the arguments friends have. Every program follows the same rules: public data only, no accounts, nothing about you stored on a server, and the whole method written down on a page like this.

Contact

Questions and corrections to how the site works: a public contact address is being set up and will appear here; this page is regenerated on every build. See also Legal & privacy.

Lights Down is a free tool: tell it your streaming services and how long you have, and it ranks what you can stream tonight, with a this-or-that, a roll, a bracket and a wheel. Movie data from TMDB; streaming availability by JustWatch. Page updated 2026-09-23. This product uses the TMDB API but is not endorsed or certified by TMDB. Lights Down is a Somebody Decide program. How the data works · Legal & privacy · Tonight's lists