What are key, fill and back light, where do open primary sources say to put them, and what goes wrong?

Four openly readable sources (a 1953 Eastman Kodak amateur-film magazine, a 1949 cinematographer's book, a 1998 university hypertext, a CC-licensed college handbook) agree on the roles: key = principal light that sets shape and mood and is placed first; fill = weaker, more diffuse light on the shadow side; back light = rear/above light that outlines and separates. They differ on exact angles, so angles are starting positions, not rules. Curator correction 2026-10-24 (discovery audit record C3-B1091-02, curator-reviewed C3R-0697; excerpts re-located by independent curator GET 2026-10-24): Correction. C3-B026-G7-01 says one of its four sources is 'a 1953 Eastman Kodak amateur-film magazine'. The cited source, Movie Makers vol. 28 (1953), is published by the Amateur Cinema League, Inc. of New York, not by Eastman Kodak; the same volume carries Kodak-related articles and advertising, but Kodak is not its publisher. The statement was wrong when written (the volume's masthead said so then). The record's lighting content is not affected: the Heffernan passage on key, fill and back light is quoted accurately, and the key light is placed first because it 'establishes the lighting key or mood'. Corrected description: a 1953 Amateur Cinema League amateur-film magazine (Movie Makers, article by Leo J. Heffernan on incident light meters). Curator qualifications: Key/fill/back roles and the named failure modes verified across three of four sources. The flagged fill-position disagreement is real (Alton: fill as near the camera as possible; SIGGRAPH/LibreTexts: angled opposite the key) and is correctly framed as differing conventions, not a measured rule. Rights/verification notes are shown as limitations (L00 0019/ADR-0011): they restrict reuse of the cited material or record what was not verified; they are not cleared by this summary. Limitations: [component_reuse_restriction] Alton 1949 text public-domain status not verified; LibreTexts CC licence per producer. Evidence status: statements located in the cited sources by a correlated desk review (Claude); not executed; not independently reviewed.

{
  "citations": [
    {
      "url": "https://education.siggraph.org/static/HyperGraph/lighting/lighting_film_video.htm",
      "note": "work/sg.raw SIGGRAPH HyperGraph lighting page; work/alton.txt Alton, Painting With Light (1949) DLI djvu text; work/lt.txt LibreTexts 9.06 Lighting Design"
    },
    {
      "url": "https://human.libretexts.org/Bookshelves/Theater_Film_and_Storytelling/Video_Production_Handbook/09%3A_Lighting/9.06%3A_Lighting_Design",
      "note": "work/sg.raw SIGGRAPH HyperGraph lighting page; work/alton.txt Alton, Painting With Light (1949) DLI djvu text; work/lt.txt LibreTexts 9.06 Lighting Design"
    },
    {
      "url": "https://archive.org/download/in.ernet.dli.2015.167927/2015.167927.Painting-With-Light_djvu.txt",
      "note": "work/sg.raw SIGGRAPH HyperGraph lighting page; work/alton.txt Alton, Painting With Light (1949) DLI djvu text; work/lt.txt LibreTexts 9.06 Lighting Design"
    }
  ]
}