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The second distinct period of lightness work took place between 1911 and 1930. In the thirty-five years following Ewald Hering's Outlines of a Theory of the Light Sense, no important theoretical developments in lightness took place until the publication in 1911 of David Katz's book (translated into English in 1935 as The World of Colour). For the next two decades, Katz's work dominated the field of lightness. Katz himself was not a Gestalt psychologist, nor was he a theorist of any note. His theoretical ideas did not deviate substantially from those of Hering and Hermann von Helmholtz. However, Katz broke new ground in phenomenology and experimentation, and he was respected by the Gestaltists on both counts.

Chronologically the fourth period of lightness theory, also known as the contrast period, extended from World War II until the end of the 1960s. Ideologically, however, it began at the end of the 19th century, ignoring the intervening work of David Katz and the Gestalt psychologists. The contrast period was dominated by the behaviorists, who believed in the physiological mechanism of lateral inhibition. Contrast theorists took up the debate right where it had been left off in 1900, amidst the Ewald Hering/Hermann von Helmholtz controversy — and they sided overwhelmingly with Hering. Two theories came to dominate this period, those of D. Jameson and L. Hurvich and of Tom Cornsweet, both derived from Hering. Other important theories of the time, such as Harry Helson's adaptation-level theory and Hans Wallach's ratio theory, were assimilated to Hering's theory of contrast.

This chapter argues that the overall pattern of errors in human lightness perception offers a powerful method for identifying the kind of software used by the lightness system. In a systematic survey of lightness errors, it is demonstrated that many of the errors predicted by lightness theories do not occur, and many of the errors that do occur are not predicted by the theories. The computational models fail to account for errors, and error-driven models are proposed here.

This chapter outlines and critiques all the main theories of lightness, laying out the strengths and weaknesses of each. These include the past experience theories, contrast theories, brightness models, decomposition models, and anchoring theory.

This chapter examines theoretical positions on the closely related question of perception of the illumination. An important theoretical question, closely related to the question of how well illumination is perceived, concerns the relationship between perceived illumination and perceived surface lightness. Four major positions can be distinguished: lightness is derived from perceived illumination; lightness and perceived illumination are mutually dependent, but neither is prior; lightness and perceived illumination are simply independent; veridicality of lightness and perceived illumination are negatively correlated.

The phenomenology of color constancy, with both illumination-dependent and illumination-independent elements, presents a challenge to both philosophy and vision science. There is considerable evidence, both formal and informal, that there is a separate illumination-dependent aspect to color appearance in some sense of “appearance.” How to conceive of this illumination-aspect of color constancy is less clear, with at least two reasonable alternatives on the table. The empirical evidence required to discriminate between the pure perception and the sensory core plus judgment alternatives is mostly unavailable, although there is some suggestive evidence from lightness constancy. The usual language in which these hypotheses are formulated is ambiguous, and this confuses the issues even further.