The lamp house is the enclosed, light tight upper housing of a photographic enlarger or projector that contains and surrounds the light source used to illuminate the negative or transparency during the exposure or projection process. It is a fundamental structural and functional component of the enlarger or projector, serving both to house and protect the lamp and its associated optical and heat management components, and to prevent stray light from escaping and causing fogging of photosensitive materials in the darkroom or unwanted spill light in a projection environment.
In a photographic enlarger, the lamp house sits at the top of the enlarger column above the negative carrier and lens, and its primary function is to produce a bright, even, and consistent illumination of the negative that will result in a uniformly exposed print across the full image area. The design and optical configuration of the lamp house has a significant influence on the quality and character of the light reaching the negative, and different lamp house designs produce distinctly different printing characteristics. Condenser enlargers use a lamp house containing one or more condenser lenses to focus and direct the light from the source in a concentrated, parallel beam through the negative, producing sharp, high contrast prints with pronounced grain and fine detail. Diffuser or cold cathode enlargers use a lamp house fitted with a diffusing panel or a large area fluorescent light source to produce a soft, even, and directionless illumination that gives smoother tonal gradation, reduced grain visibility, and a more forgiving response to dust and scratches on the negative surface.
The lamp house also incorporates heat management features to protect the negative and other optical components from the heat generated by the light source during extended printing sessions. These may include heat absorbing glass filters, ventilation slots or fans, and reflectors designed to direct heat away from the negative stage. In colour enlargers, the lamp house additionally contains a set of colour filtration dials or a colour head with variable cyan, magenta, and yellow filters that allow the colour balance of the enlarging light to be adjusted for colour printing or variable contrast black and white printing.
In slide and movie projectors, the lamp house performs the same fundamental function of housing the light source and directing its output through the transparency or film gate, with similar considerations of even illumination, heat management, and the prevention of stray light affecting the viewing environment.