Colour-rendition properties of solid-state lamps

Abstract

The applicability of colour quality metrics to solid-state light sources is validated and the results of the assessment of colour rendition characteristics of various lamps are presented. The standard colour rendering index metric (CRI) or a refined colour quality scale metric (CQS) fail to distinguish between two principle colour rendition properties of illumination: the ability to render object colours with high fidelity and the ability to increase chromatic contrast, especially when the spectra of light sources contain a few narrow-band electroluminescence components.Supplementing these metrics by the known figures of merit that measure the gamut area of a small number of test colour samples does not completely resolve this issue. In contrast, the statistical approach, which is based on sorting a very large number of test colour samples with respect of just perceivable colour distortions of several kinds, offers a comprehensive assessment of colour rendition properties of solid-state light sources. In particular, two statistical indices, colour fidelity index (CFI) and colour saturation index (CSI), which are the relative numbers of object colours rendered with high fidelity and increased saturation, respectively, are sufficient to reveal and assess three distinct types of solid state light sources. These are (i) high-fidelity lamps, which cover the entire spectrum with the spectral components present in the wavelength ranges of both 530-610 nm and beyond 610 nm (e.g. trichromatic warm white phosphor converted LEDs, red-amber-green-blue LED clusters, complementary clusters of white and coloured LEDs); (ii) colour-saturating lamps, which lack power in the 530-610 nm wavelength range (e.g. red-green-blue or red-cyan-blue LED clusters); and (iii) colour dulling lamps, which lack power for wavelengths longer than 610 nm (dichromatic daylight phosphor converted LEDs and amber-green-blue LED clusters). Owing to a single statistical format, CSI and CFI can be used for design and optimization of multiwavelength LED clusters providing "smart" illumination with a trade-off between different colour rendition characteristics.

Towards 10 Gb/s orthogonal frequency division multiplexing-based visible light communication using a GaN violet micro-LED

“…For generation of white light for illumination, the use of violet-emitting LEDs exciting tricolor (red, green, and blue) phosphors also offers advantages over the widely used method of combining blue direct LED emission with a yellow-emitting phosphor. These include much superior color rendering indices [9,10] and the absence of a direct blue component, which has proven to be disruptive to the human circadian rhythm [11]. The micro-LED die shapes employed in this work are also expected to be advantageous for efficient light extraction, by analogy with previous designs employing non-circular emitting areas [12].…”

Synthesis, optical, photocatalytic, and electrochemical studies on Ag2S/ZnS and ZnS/Ag2S nanocomposites

“…Different combinations of metal oxides and metal sulfide have been extensively examined as potential photocatalysts for the degradation of organic dyes (Reddy et al 2007;Wu and Chern 2006). Heterogeneous photocatalysis is a good method for the decontamination and mineralization of organic pollutants because of its high efficiency, low-energy consumption, and satisfactory environmental compatibility (Su et al 2008;Ž ukauskas et al 2010). In view of this, ZnS and Ag 2 S with band gap energy of 3.6 and 0.9 eV, respectively, are considered to be good photo-responsive catalysts.…”

Efficient cerium-based sol–gel derived phosphors in different garnet matrices for light-emitting diodes

“…Commercial phosphor conversion white LEDs with YAG:Ce as a single phosphor are quite efficient, but have high correlated color temperature (>5000 K) due to the lack of emission in the red region. Consequently, the color rendition ability of these daylight dichromatic LEDs is insufficient for general lighting and other lighting applications requiring high color fidelity [2].…”