HIGH KEY A term applied to a photographic print or subject consisting entirely of light tones with little contrast; also applied to a method of lighting a subject.

HIGHLIGHT The bright parts of a picture or subject that are rendered as dense areas in the negative and by very low density in the print.

HUE That attribute of certain color perceptions in respect to which they differ characteristically from the gray of the same lightness and which permits them to be classed as reddish, yellowish, greenish, or bluish.

HYDROMETER Generic term for various instruments designed to determine the specific gravity of liquids. (PIA)

HYDROQUINONE C6H4(OH)2 Common photo-graphic developing agent para-dihydoxybenzene.

HYPERFOCAL DISTANCE The distance from the optical center of lens forward to the nearest plane in acceptable focus when the lens is focused at infinity distance.

ILLUMINANCE Luminous flux incident per unit area of a surface. Widely known as illumination.

IMAGE, LATENT The invisible image produced by the action of radiant energy on a photosensitive surface. It may be made visible by the process of photographic development.

IMAGE, NEGATIVE A photographic image in which the values of light and shade of the original subject are represented in inverse order. In a negative, light objects are represented by high densities and dark objects are represented by low densities.

IMAGE, POSITIVE A photographic image in which the values of light and shade of the original subject are represented in their natural order. In a positive, light objects are represented by low densities and dark objects are represented by high densities.

IMAGE PLANE The plane in which the image lies or is formed It is perpendicular to the axis of the lens. A real image formed by a converging lens would be visible upon a screen placed in this plane.

INCANDESCENT Glowing with heat, such as the tungsten filament in an incandescent lamp.

INCIDENCE The act of falling upon or affecting, as light upon a surface.

INFINITY A distance so far removed from an observer that the rays of light reflected to a lens from a point at that distance may be regarded as parallel. A distance setting on a camera-focusing scale.

INFRARED Pertaining to or designating those rays which lie just beyond the red end of the visible spectrum. They are invisible and are detected by their thermal, photoelectric, and photographic effects. Their wavelengths are longer than those of light and shorter than those of radio waves.

INTERNEGATIVE An internegative film is a negative derived directly from a color reversal original film. All other color-duplicating negatives derived from any other than reversal film are known as color-duplicating negatives regardless of the generation.

INVERSE SQUARE LAW The intensity of light received at a point (irradiance) varies inversely as the square of the distance from the source. The law holds for relatively small sources only and is useful in calculating photographic exposures. (PIA)

IRIS DIAPHRAGM Term applied to the adjustable aperture fitted into the barrel of the photographic lenses and so-called because of the contraction of the aperture resembles that of the iris (pupil) in the human eye. It consists of a series of thin metal tongues overlapping each other and fastened to a ring on the lens barrel, the aperture made smaller or larger by turning the ring. (PIA)

JOGGING Frame-by-frame advancement of videotape.

KELVIN (K) Measurement of the color of light in degrees. Numerically, the Kelvin temperature is equal to the Centigrade temperature plus 273 degrees.

KEY LIGHT The main source of illumination on a subject. (PIA)

LAMP, PHOTOFLOOD A lamp designed to yield brilliant diffuse illumination. These lamps are generally short-lived. (NMA)

LAMP, REFLECTOR FLOOD Light bulb with self-contained silvered surface to act as a reflector.

LAMP HOUSE That portion of an enlarger, reader, or projector that contains the light source and condensers or mirror.