Changing colours: now you see them, now you don’t

Abstract

Nature offers a range of colour displays which are relatively short‐lived and which were for many centuries little understood. Today we can explain most which arise from diffraction and reflection effects on rays of sunlight, various atmospheric ionisation phenomena and many colour effects resulting from biochemical reactions, although less is understood about some of the strange psychedelic patterns and colours which our brains can sometimes produce. The practical purposes to which certain fluorescent, thermochromic and photochromic dyes can be put, including their presently limited textile applications, are illustrated.

Assessing the variability of colour‐rendering indices using a random test‐colour method

“…As expected, for both indices, the greatest discrepancies between the declared official values and those found with the 6000 samples occurred for the high-pressure sodium source, for reasons indicated above. Figure 5 shows the change in the internal-type standard deviation [Eqns (8) and (9)] for 100 iterations made, as a function of the number of samples used to calculate the R a index (n = 10, . .…”

“…Given that the R a and R 0 f values are calculated as the average of the colour differences on specific sets of samples [Eqns (1) and (3)], we can calculate the standard deviations of these colour differences [Eqns (2) and (4)] on each of these sets of samples using Eqns (8) and (9). These standard deviations of the R sample values of a set of specific samples [Eqns (8) and (9)] will be called 'internal standard deviations', as opposed to the standard deviations calculated using Eqns (12) and (13), which are the deviations calculated on 100 iterations with different sets of samples, and will be called 'external standard deviations'. Trying to estimate the uncertainty of CRIs using different sets of random samples, it might be thought that the most useful parameter would be the external standard deviation, but it will be demonstrated in the next section that there is a strong correlation between the external and internal standard deviations.…”

Control of optical properties through photochromism: a promising approach to photonics

“…The first set of diarylethenes (1)(2)(3)(4)(5) shows the effect of the presence of electroactive substituents on the absorption maxima of the colored form. Comparison to the unsubstituted molecule (1) evidences that electrodonating groups cause a redshift of the absorption band while an ipsochromic effect results from substitution with acceptor Table 2 Absorption maxima (in chloroform solution) for the colored form of diarylethenes as function of the chemical structure.…”

“…Several stimuli are known to induce a change in color of suitable materials [1,2]. When the change is induced by light, we refer to photochromism.…”

The chromic and electrochemical response of CoCl2 − filled polyimide materials for sensing applications

“…In recent years, chromic materials are generally employed in high-tech non-textile applications which exploited the chromic effect generated by the stimulus, for instance in thermometry, electronics, ophthalmics, photonics, biomedicine, etc. [2][3][4][5][6].…”