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Raking Light
Quick answer: Raking light is lighting aimed across a surface at a very shallow angle to reveal texture and defects by casting tiny shadows and highlights.
What it means
When light skims across paint at a low angle, even small height differences show up clearly. Swirls, sanding marks, holograms and unlevelled coating patches become visible because the grazing light exaggerates their contrast. Hand-held, high-CRI LEDs and slim panel lights are commonly used for this inspection technique.
Why it matters
Correction is limited by what you can see. Overhead strip lighting flatters paint, and a panel that looks finished under it will show a full set of holograms the moment a light source is brought round to a low angle. Working without that angle means correcting the defects you happened to notice rather than the ones that are there.
Low-angle light exposes swirls, haze, holograms, dust nibs and orange peel, and it does the same job again once protection goes on, making high spots, overlaps and rainbowing visible during the levelling window. It is also how correction gets checked for consistency panel by panel before anything is applied over it. Colour rendering matters as much as angle: a high-CRI source shows the finish as it is, where a cheap light casts colour that hides exactly the faults being looked for.
Where raking light is used
Paint correction stages, coating application and final quality control all depend on it, normally in a controlled indoor bay with adjustable lighting. Job sheets and inspection notes record checked under raking light, holograms visible under raking light or panel passed final QC, and detailers use the phrase when explaining why a car needs to be seen indoors rather than assessed on a driveway.
Context
Raking light is the first thing our workshop reaches for after any correction stage; what looks like a clean panel under the overhead strip lights can show up a full set of holograms under a hand lamp at 10 degrees, and it is always better to find them before the coating goes on.
Common mistakes
- Relying on bright overhead light only, which flattens defects rather than revealing them.
- Using low-CRI torches that hide fine marring or shift colour.
- Holding the light too close and on-axis, blowing out highlights and masking texture.
- Not changing angles or viewing distance, so overlaps and edges are missed.
- Trusting a phone torch for final QC - it is rarely bright or accurate enough.