Light Flashcards
What is the visible wavelengths for humans?
380nm (blue) to 780nm (red)
What is the equation to calculate the wavelength of light?
Wavelength = speed/frequency
Speed of light =3.0 x 10*8 meters per second
What is a photon?
A unit or ‘packet’ of light which interacts individually with atoms
Each photon had an energy which is dependant on the frequency of the light
Energy of photon = plancks constant (h) x frequency
Plancks constant = 6.626 x 10*-34 J s
The higher the frequency of light, the lighter the energy, therefore blue light has more energy
What is white light?
A mix of the visible frequencies of light
What is monochromatic?
A source which emits light of on,y one wavelength and therefore are of one colour…i.e sodium street lamps
What is Luminance?
The amount of light coming from a surface
A luminance profile (L) can be formed by multiplying the illuminance (I) x reflectance (R)
Illuminance = amount of light falling on a surface Reflectance = the amount of light reflected from a surface
How are reflectance and illuminance perceived?
Lightness and brightness respectively
What is albedo?
The reflectance of a surface such as sea, ice and land
Define diffuse and specular reflection….
Diffuse reflection = the reflection of light in a haphazard way such as a Matt irregular surface - unpredictable
Specular reflection = the reflection of light in an ordered way such as mirrors - predictable
Why do objects appear coloured?
They absorb some wavelengths of light and reflect others
Name the two models of light propagation
Wave model…similar to sound waves
Quantum model …. Light considered as photons of energy
Name the six hues…
Red, yellow, green, blue, black and white
See hue circle pg.. 19
What is an achromatic colour?
A colour without hue… i.e grey
The opposite of chromatic colours…. With hue
Name the additive primary colours and what colours can they make when mixed?
Red, blue and green
Red + blue = magenta
Red + green = yellow
Blue + green = cyan
Name the subtractive primary colours and the colours they make once mixed?
Cyan, magenta and yellow
Cyan + magenta = blue
Cyan + yellow = green
Magenta + yellow = red
