Fundamental Spectral Boundaries of Circadian Tunability

Abstract

The discovery of melanopsin and the non-visual impact of light, lead to a new era in lighting design. Using a melanopic action spectrum, the CIE introduced the melanopic efficacy of luminous radiation (MELR), which quantifies the influence of light on melanopsin. A significant amount of research has been conducted on the possible variation of this MELR and other related metrics for various practical lighting settings, but the fundamental spectral boundaries have not yet been disclosed. Without these limits, it is difficult to assess if a certain lighting system really achieves high or low MELR. This paper determines these fundamental MELR boundaries for different CCT and certain minimal TM-30 R f values, using a a flexible parametrization of the light source spectrum that is optimized with Differential Evolution. The obtained results show that with increasing CCT, the interval between the theoretical MELR extrema increases slightly, while the opposite occurs when increasing the minimal TM-30 R f value. The same parametric model and optimization approach is also used to determine the maximal Luminous Efficacy of Radiation (LER) within the obtained MELR limits.

Correlated color temperature is not a suitable proxy for the biological potency of light

“…Figure 6 also shows that as the color fidelity floor is raised (i.e., from R f ≥ 70 to R f ≥ 80 to R f ≥ 90), the mean and spread of achievable mel-DER values decrease at any single CCT. This is consistent with the results of Carpentier and Meuret 39 . (Note that when color fidelity is maximal—i.e., IES TM-30 R f = 100—the ranges shown in Fig.…”

“…A clear trend between mel-DER and CCT is evident where, on average, mel-DER increases as CCT increases ( r 2 > 0.86). This trend is consistent with that demonstrated by Zandi et al 38 , Carpentier and Meuret 39 , and Spitschan 40 . Summary statistics are provided in Table 1 and can be used to estimate mel-DER for an SPD based on CCT and IES R f .…”

Smooth output from adaptive illumination systems with pixelated LED arrays

“…When integrated with a camera, the PSFs can be fully characterized, and accurate tailoring can be achieved via least-squares calculation. 15 However, many illumination systems require a smooth irradiance pattern, in order to maximize visual comfort. This paper presents a preprocessing method of the target irradiance pattern for least-squares pixel activation, to ensure a smooth resulting illumination pattern.…”

“…This equation can be solved using the least-squares solution x = (A T A) −1 A T t. In reality, some calculated values may be negative, so a bounded-variable least-squares (BVLS) algorithm is used to find a solution with non-negative constraints on x. For a full, in-depth explanation, we refer to Cerpentier et al 15…”

“…Recent work by Cerpentier et al has demonstrated an efficient, deconvolution-based least squares algorithm to solve this inverse problem. 15 However, it may be argued that for illumination applications, it is more important to have a smooth illumination pattern than having an optimal match with the detected object(s). This paper introduces a computational, image-processing based approach to attain adaptive LED array illumination with smooth output.…”