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

• 5000-4500 k: Xenon lamp/light arc

• 5500 k: Sunny daylight around noon

• 5500-5600 k: Electronic photo flash

• 6500-7500 k: Overcast sky

• 9000-12000 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/m2 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

Mean reflectance values of some common colored surfaces

Surface color ReflectanceWhite 80Light gray 50Dark gray 20Ivory white 80Ivory 70Fawn 50Buff 50Tan 40Brown 30Cream 50Green 40Olive 20Azure blue 50Sky blue 40Pink 60Red 20

Additional information

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