The influence of light path length on the color of synthetic ruby

The corrected ultraviolet–visible light spectrum was used to calculate the color of synthetic rubies with different light path lengths, and the influence of light path length and standard light source on the color of synthetic ruby was studied. The results show that the difference in colour between the o light direction and the e light direction of the synthetic ruby decreases as the length of the light path increases. At the same time, as the length of the light path increases, the lightness L* decreases, and the hue angle h° increases. The chroma C* first increases as the length of the light path increases, and then begins to decrease under the influence of the continuous decrease in lightness. The color difference ΔE*(ab) reaches the maximum when the light path length is around 10 mm, and the standard light source has the greatest influence on the color difference ΔE*(ab). As the length of the light path continues to increase, the influence of the standard light source on the color difference ΔE*(ab) decreases. In the ultraviolet–visible light spectrum, the strong absorption band of Cr(3+) at 545 nm is the main cause of the color of the ruby. The larger the area of the band at 545 nm, the lower the lightness and the higher the hue angle, which means the ruby colour is redder.