Definitions 1 Flashcards
Additive color mixing
The process of mixing different lights together to create more light energy in the composite mixture.
Adaptation
Process by which the visual system becomes accustomed to more or less light or a different colour than it was exposed to during an immediately preceding period.
Aqueous humor
Clear, water like substance that lies between the cornea and the lens. Provides nutrients, including oxygen, to the cornea and lens. Helps maintain the smooth, curved shape of the cornea.
Blackbody locus
The locus of points on a chromaticity diagram representing the chromaticities of blackbodies having various color temperatures.
Blind spot
Where the optic nerve exits the back of the eyes. Receptor cells absent at this location on the retina.
Candela, cd
The SI unit of luminous intensity. One candela is one lumen per steradian.
Candela per square meter, cd/m sq.
The SI unit of luminance equal to the uniform luminance of a perfectly diffusing surface emitting or reflecting light at the rate of one lumen per square meter or the average luminance of any surface emitting or reflecting light at that rate.
Chromaticity diagram
A two dimensional graph formed by plotting one of the three chromaticity coordinates against another.
Color
One of the five factors influencing a persons ability to see an object or detail. Difficult to assess.
Color perception
Involves the brain interpreting the information in the form of electrical signals that it receives from the eyes. Three types of cones in the eye provide ability to distinguish color.
Color rendering index (CRI)
A number between 1 and 100 used to describe the ability of a lamp to accurately render all of the colors in a lit space.
Color temperature
The absolute temperature of a blackbody radiator having a chromaticity equal to that of the light source.
Correlated color temperature (CCT)
Describes the overall color appearance of a lamp. Measured in Kelvins (K).
Cones (eye)
Light receptor cells in retina. Responsible for color, or photopic vision.
Contrast
Magnitude of the luminance difference between an object and its background divided by the background luminance.
Cornea
Translucent membrane that is the forward most surface on the eye.
Dark adaptation
Adaptation of the rods to very low light levels.
Direct glare
Any excessively bright source of light, coming directly into the eyes, causing discomfort and/or a loss in visibility.
Disability glare
Effect of stray light in the eyes that causes a reduction in visual performance and visibility.
Discomfort glare
Direct glare caused by a light source in the field of view that makes vision uncomfortable but does not necessarily interfere with visual performance or visibility.
Eye
Receiver of light stimuli and initiator of neural processing.
Footcandle, fc
The unit of illuminance where the foot is taking as the unit of length. It is the luminance on a surface one square foot in area in which there is a uniformly distributed flocks of one lumen, or the luminance produced on a surface all points of which are at a distance of one foot from a directionally uniform point source of one candela.
Fovea
Small pit (approximately 1.5 mm diameter) in the center of the eyes that is responsible for our highest visual acuity (acuity to distinguish fine details).
Glare
The sensation produced by luminance within the visual field that is sufficiently greater than the luminance to which the eyes are adapted to cause annoyance, discomfort, or loss in visual performance and visibility.
High contrast
A lighting condition characterized by a large portion of focused light on an object or the foreground and a small amount of diffuse light on the background.
Illuminance, E
The density of the luminous flux incident on the surface; it is the quotient of the luminous flux by the area of the surface when the latter is uniformly illuminated. Light striking a perfectly diffusing surface.
Iris
Colored bring surrounding the pupil, which contains muscles that cause the people to dilate and constrict to increase or decrease the amount of light entering the eye.
Lamp
A source that converts electricity into light. The official industry term for lightbulb or fluorescent tube. All light sources are referred to as lamps in the lighting industry.
Landolt C’s
Test for visual acuity, where the subject must detect the orientation of the gap in a round letter C.
Lens
Optical component that lies behind the pupil, which changes shape to adjust the amount of optical power needed to focus objects that lie at different distances in space onto the retina at the back of the eye.
Light adaptation
Photochemical adaptation in the photoreceptors, which involves the rod and cone cells reaching a balance point in the amount of bleached versus unbleached photopigment they contain.
Low contrast
Alighting condition characterized by a large portion of diffuse light and a small amount of focused light.
Luminance, L (cd/m sq.)
The objective measure of the intensity of light entering the eyes, per unit of projected area. It is they excepted term for light that is reflected from the surface in a given direction toward the eyes. Properly defined as intensity of flux leaving a surface in a given direction. It is measured in candelas per square foot (cd/ft sq.) or candelas per square meter (cd/m sq.)
Luminance ratio
Luminance differences in a persons field of view.
Luminous intensity, I (cd)
The luminous flux per unit solid angle in a specific direction. Hence, it is the luminous flux on a small surface normal to that direction, divided by the solid angle (in steradians) got to the surface subtends at the source.
Lux, lx
The SI unit of illuminance. It is the illuminance on a surface one square meter in area on which there is a uniformly distributed flux of one lumen, or the luminance produced had a surface all points of which are at a distance of one meter from a uniform point source of one candela.
Macula
7mm diameter region on the retina that is responsible for our detailed vision; contains only cones.
Mesopic
Range of the luminance levels where the response of our eyes does not follow either the photopic nor scotopic response curves.
Modifier
Changes light reflected from or transmitted through an object or surface (i.e., no longer direct light source) and then directs light into our eyes, where it is processed by the visual system.
Optic nerve
Nerve transmits electrical impulses from the retina to the brain.
Optical components
Components of the eyes that are responsible for focusing light onto the retina at the back of the eye, which begins the process of visual perception. Include the cornea, marquis humor, the lens, the iris, and the vitreous humor.
Photopic
Color vision, as interpreted by cone cells.
Photopigments
Chemicals that absorb light energy and convert to an altered state.
Presbyopia
Loss of ability to focus on near objects.
Pupil
Round, dark opening in the iris.
Reflectance factor
Also called reflectance. The ratio of incident light to reflected light.
Reflected glare
Glare from surfaces in the environment, which may produce similar discomfort, as when direct sunlight is admitted to a space.
Retina
Innermost layer of the eye that contains receptor cells, nerve cells, and blood vessels that supply nutrients to the cells.
Rods
Light receptor cells responsible for low level night, or scotopic, vision.
Scotopic vision
Low level, or night, vision.
Size (for visual purposes).
The visual angle subtended at the eye by the object’s detail.
Snellen eye chart
Visual acuity test using letters, numbers, or pictures in lines of decreasing sizes.
Source
Emitted light (from the sun, an electric lamp, etc.) that interacts with objects and surfaces in space.
Specular
Having the reflecting properties of a mirror-like surface. The angle of reflection is equal to the angle of incidence.
Spectral power distribution
Radiant energy per unit wavelength interval, considered within the extents of the visual spectrum. The units are typically watts/nm, but can be presented in units of percentage.
Subtractive color mixing
The process of removing light by absorption. With opaque media, this is often achieved by mixing pigments to create darker colors, thus reducing (i.e. subtracting) the light that can be reflected from the mixture. With translucent media, such as filters, light is subtracted by the pigments that are embedded in the filter; stacking filters will subtract more light.
Veiling reflections
Specular reflections that occur from a polished or shiny surface.
Viewing time
Time wag in the photochemical processes in the retina and in the transmission/interpretation of the electrical impulses in the brain. Given sufficient time, even small details can be seen under relatively low levels of light.