Your free myERCO account allows you to mark items, create product lists for your projects and request quotes. You also have continuous access to all ERCO media in the download area.


You have collected articles in your watchlist

Technical environment

Technical environment

Global standard 220V-240V/50Hz-60Hz
Standard for USA/Canada 120V/60Hz, 277V/60Hz
  • 中文

Our contents are shown to you in English. Product data is displayed for a technical region using USA/Canada 120V/60Hz, 277V/50Hz-60Hz.

What are constancy phenomena?

Illustration with three flat shapes shown laterally in different perspectives, visualizing the phenomenon of constancy.

Constancy phenomena are processes of correction in vision and an essential precondition for constructing an orderly image of reality. Constancy in this sense is the ability to recognise constant objects, even when their size, shape, reflectivity and colour or the surroundings change. These include, among other factors, changes in distance, spatial position or lighting.

Overview of the topic constancy phenomena

ERCO Light Knowledge is also available as a whitepaper:

What is perceptual constancy?

The same object generates different retinal images in the eye due to changes in lighting, distance or perspective. For example, due to change in shape, size or distribution of brightness. Perceptual constancy enables us to identify recurring objects and their properties and to perceive these as being constant.

Which types of constancy phenomena are there?

There are different forms of perceptual constancy in vision. These cannot, to a certain extent, be influenced or controlled. Types of perceptual constancy include:

  • Size constancy

  • Brightness constancy

  • Color constancy

  • Shape constancy

  • Constancy of perspective

What all of these have in common is that objects retain their color, shape, size and brightness despite changing conditions in terms of surroundings and lighting.

What is meant by size constancy?

For visually perceiving size, a compensation for the perspective distortion of objects takes place. This ensures that e.g. rectangular or circular shapes as spatial phenomena are perceived constantly: the observer can thus constantly recognize regularly arranged circles on the ceiling as being the same size, although the circles visually shrink with increasing distance and look more like ellipses.

What is brightness constancy?

A further phenomenon of constancy is brightness constancy. The perceived brightness results from the ratio of brightness of the object viewed and brightness of the immediate surroundings. For example, a medium gray field with a dark surrounding is seen as being light gray. If the surrounding is light, the field appears dark gray. This phenomenon can be explained by the direct processing of incoming stimuli. This visual impression of two apparently different shades of gray is exclusively based on sensory impressions coming from the outside.
Constancy phenomena: a medium gray wall in an otherwise white room becomes dark gray.

The perception of the brightness of the gray field depends on the surroundings; in a bright surrounding, an identical gray appears darker than in a dark surrounding.

Constancy phenomena: a medium gray wall in an otherwise dark room becomes light gray.

What is color constancy?

As with the perception of brightness levels, color perception is also dependent on peripheral colors and the type of lighting. The need for interpreting color impressions comes about mainly due to the constantly changing light colors in the environment. For example, a white sheet of paper is perceived constantly both in the bluish light of the sky and in warmer, direct sunlight. Color constancy in vision corresponds to the white balance of film and photo cameras. Color photos taken under identical conditions without white balance show the expected, distinct color casts of the respective type of lighting.
Hill with wind turbine against a dark sky. Hill with wind turbine against a light blue sky. Hill with wind turbine against a reddish sky. Hill with wind turbine against a sunrise.

Good to know: Based on long experience, the observer does not evaluate shadows as color-changing.

What is meant by shape constancy?

Constancy of shape, or form constancy, is also one of the constancy phenomena. Our experience teaches us that gradients in luminance from light to dark or vice versa can result from the spatial shape of an illuminated object. Examples are the formation of typical shadows on three-dimensional bodies such as cubes, cylinders and spheres.

The example of a hemisphere on a plane demonstrates how the incidence of light and the progression of shadows influence the perceived shape:

Illustration of an apparently convex circle curved towards the observer.

The positioning of the light incidence from above determines the spatial impression.

Illustration of an apparently concave circle curved away from the observer.

When the image is rotated, elevation and depression change positions.

ERCO Light Knowledge is also available as a whitepaper:

Further topics on seeing and perceiving

Do you need further information?

You can contact your regional contact partner via:

You can gladly send us an e-mail or ask your question here

Your data will be handled confidentially. For further information see Data protection declaration.




Planning light

About ERCO