Alexandrite-like effect in purple flowers analyzed with newly devised round RGB diagram.

Ichiro Kasajima

doi:10.1038/srep29630

Abstract

The gemstone alexandrite is known for its feature to change color depending on the spectral quality of the incident light. Thus, the stone looks green when illuminated by white LED light but looks red when illuminated by incandescent light. This effect (alexandrite effect) is caused by a special relationship between the spectral quality of the incident light and the absorbance spectrum of the stone. Here we report an alexandrite-like effect in the petals of torenia and cyclamen flowers. These flowers are purple in sunlight but magenta (reddish) in incandescent light, and violet (bluish purple) in white LED light. The m-n, triangle and round diagrams are devised to calculate the colors of visible light spectra, based on the RGB color-matching function. Using these calculations, the alexandrite-like effect in purple flowers was successfully analyzed in terms of the interaction between the incident light spectrum and the absorbance spectrum of their purple anthocyanin. This analysis allows both logical and intuitive understanding of the colors exhibited by any object showing alexandrite–like properties.

Highlights

‘Psycho-physical’ reaction of the human eye to visible light spectrum is quantified with ‘color matching functions’ released from Commission Internationale de l’Eclairage (CIE)
These analyses clarify the nature of interaction between light transmission/reflection of substances and psycho-physical reaction of the human eye, that result in alexandrite effect
The round diagram is similar to the popular HSV and HSL color spaces[10]

Summary

Introduction

‘Psycho-physical’ reaction of the human eye to visible light spectrum is quantified with ‘color matching functions’ released from Commission Internationale de l’Eclairage (CIE). Colors are plotted on various different diagrams derived from color matching functions These diagrams were developed to intuitively discriminate colors according to three color factors, lightness (brightness), hue (e.g. red, green, blue) and saturation (vividness). This report developed new color diagrams based on RGB color matching function, using triangular color vectors One of these diagrams which was named ‘round diagram’ enables plotting all colors on a circle, according to their hues and saturations. Hue and saturation of these substances were calculated with RGB color matching function, and plotted on round diagram. These analyses clarify the nature of interaction between light transmission/reflection of substances and psycho-physical reaction of the human eye, that result in alexandrite effect

Methods

Results

Conclusion