Colour brightness

In this resource, the term colour brightness is used to refer to how things appear to a human observer in terms of their perception of colour.

Colour is what humans see in the presence of radiated or reflected light.
The brightness of the colour of an object or surface (its colour brightness) depends on the wavelengths and intensity of light that falls on it and the amount it reflects.
The colour brightness of a transparent or translucent medium may depend on the wavelengths and intensity of light that falls on it and the amount it transmits or reflects.
Colour brightness often depends on the difference between the way a colour appears to an observer in well-lit conditions compared with its subdued appearance when in shadow or when poorly illuminated.
The impression of colour brightness can be affected by hue because some hues appear brighter than others to human observers. So a fully saturated yellow may appear relatively brighter than a fully saturated red or blue.

Optical factors affecting colour brightness include:
- The angle at which incidence light approaches a medium, object or surface.
- The composition of incident light in terms of wavelength, frequency and energy.
- The polarization of incident light.

Material properties affecting the colour brightness of a medium, object or surface include:
- Chemical composition
- Three-dimensional form
- Texture
- Reflectance

Perceptual factors affecting colour brightness include:
- Adjacent colours: The presence and illumination of adjacent colours can affect both the apparent hue and brightness of a target colour.
- Attributes of visual perception.

In this resource, the term brightness is associated with the intensity of light an object such as the Sun or a lightbulb emits.
The brightness of a light is always determined by comparing it with the brightness of other light sources.
As light propagates through a vacuum it is invisible but its brightness becomes apparent when a light source shines directly into our eyes or it is reflected towards us.
The perceived brightness of a light source depends on how the photoreceptive rod and cone cells in the human retina respond to wavelengths of light (rather than the way that translates into the experience of colour).

In this resource:

Brightness is used in connection with light and so with the amount, or intensity, of light an object emits.
Colour brightness is used in connection with the perception of colour.
Intensity is used in connection with the amount of light that is produced by or falls on an object.
Amplitude is used in connection with the properties of electromagnetic waves and the amount of energy they carry.