LIGHT AND SIGHT (Chapter 2) Light Wavelength Color temperature –Kelvin –Blackbody Velocity Correlated color temperature (CCT) (Additional information) –Color temperature of a light source that matches the chromaticity of a “true” color Chromaticity (Additional information) –A measure of the proportions of different primary colors in a color mixture Color rendering index (CRI) (Additional information) –A measure of the effect of the light source on the true color of objects –A CRI of 100 means that the light source does not distort the true color of the objects

Some typical color temperatures (Additional information) 1500 k: Candlelight 2680 k: 40 W incandescent lamp 3000 k: 200 W incandescent lamp 3200 k: Sunrise/sunset 3400 k: Tungsten lamp 3400 k: 1 hour from dusk/dawn k: Xenon lamp/light arc 5500 k: Sunny daylight around noon k: Electronic photo flash k: Overcast sky k: Blue sky

LIGHT AND SIGHT (Chapter 2) Sight –Adaptation –Field of vision (Additional information) The surroundings taken in by an observer's eyes, when the eyes and head don't move, is defined as the field of vision. It may sometimes be desirable to minimize movement of the eyes and head during assembly or inspection operations. Angles involved in the field of vision are: –Central (2°): A very small area involving the central part of the retina, called fovea, that provide highly detailed vision. –Near field (60° ): This area is a cone of binocular vision of 30° half-angle. It provides coarser or semi-detailed site information. –Far field and peripheral (120° - 145°): This area lies beyond the central part of the retina and provides primarily horizontal, monocular vision. This cone of vision gives very loose, subjective information about surroundings.

LIGHT AND SIGHT (Chapter 2) Photometric terms –Candlepower (Candela) –Lumen –Illuminance (some additional information) Measured in footcandle or lux Illuminance = Lumens/Area of work plane –Luminance Measured in cd/m 2 or nit (from Latin “nitere” = “to shine”) Some additional information –Luminance may be defined as measurable brightness of an object –Reflectance (Additional information) The percentage of incident light that is reflected from the surface of a material. Reflectance = (Reflected light/Incident light)*100

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LIGHT AND SIGHT (Chapter 2) Visual performance –How much light? (i.e. what should be the illuminance for a particular activity?) Variables that affect illuminance –Luminance –Size –Contrast –Time or speed –Accuaracy

BRIGHTNESS CONTRAST (Chapter 1) Contrast (Some additional information) –Attracts attention –Essential for efficient performance of visual tasks –Measuring contrast (values ranging from 0 to 1) C = |(Rb-Rt)|/Rb Where –Rb = Reflectance of background –Rt = Reflectance of task Color (Some additional information) –Three kinds of color sensors (cone cells in the retina) corresponding to red, green, blue parts of the electromagnetic spectrum –Interaction of color perception by these cells forms the basis of color vision. –Primary colors (red, green, blue) Blue and green described as “cool” Red, yellow, orange described as “warm” Color terms