Overexposed area in the frame caused by an overly concentrated light source — an unwanted brightness flare that kills detail.
Technical Details
Hot spots occur with reflection values above 90% on reflective surfaces such as metal, glass, or water. In digital cameras, brightness values above 100 IRE (Institute of Radio Engineers) lead to clipping of the video signal. Fresnel spotlights with 2K-5K wattage at distances under 2 meters from the subject are particularly critical. Typical areas where they occur are eyeglass lenses (reflectivity 4-8%), polished metal surfaces (up to 95%), and wet skin (12-15% compared to 2-5% for dry skin).
History & Development
The problem has existed since the dawn of cinematography around 1895, but intensified with the introduction of tungsten lighting in the 1920s. Arri's founders developed the first diffusion filters in 1932 to avoid hot spots. With the digital revolution starting in 2000, the problem was exacerbated by the lower dynamic range of CCD sensors (8-10 stops) compared to film (12-14 stops). Modern cameras like the Alexa 35 achieve 17 stops again, significantly reducing hot spot issues.
Practical Application in Film
Roger Deakins avoids hot spots by using large-area LED panels instead of point sources, visible in "Blade Runner 2049" in the office sequences. Unwanted hot spots are eliminated using polarizing filters (circular polarization with 45° rotation), honeycomb grids, or diffusion material like Opal Frost. In "The Matrix," Bill Pope deliberately used hot spots on sunglasses as a stylistic device for the digital world. Post-production corrections are made through highlight recovery on RAW material or local exposure adjustments.
Comparison & Alternatives
Hot spots differ from lens flares due to their static nature and lack of optical artifacts. While blown-out highlights can affect the entire image, hot spots remain locally confined. Modern LED systems like SkyPanels, due to their large-area emission, produce fewer hot spots than traditional tungsten spots. Bounced light off white walls or polystyrene boards completely eliminates hot spots but reduces light intensity by 2-3 stops.