A novel algorithm for biologically inspired lighting solutions

Light Emitting Diodes (LEDs) have attracted a lot of attention for their potential use in biologically inspired lighting. Using multiple LEDs, it is possible to create lights that differ in the excitation of only a given class of photoreceptors in the human eye, which are regarded as metamers. However, there are dramatic shifts in the output spectra of LEDs and precise spectral control of a multi-primary LED is an extremely challenging task.

Oxford researchers have developed a novel method to generate metamers with non-linear light sources using an algorithm which incorporates spectral shifts in real light sources. The algorithm would be useful for all settings in which the spectrum of a multi-primary light source needs to be precisely controlled such as in modulating alertness and sleep patterns.

Biologically inspired lighting

Light emitting diodes (LEDs) are widely used for various lighting applications, including display backlighting, automotive lighting and mobile applications. The global LED lighting market is expected to increase at a high growth rate and will reach $80 billion by 2020. In particular, human-centric or biologically relevant lighting, which requires precise control of intensity, colour and level, will dominate the lighting space.

Melanopsin is involved in the regulation of the sleep-wake cycle, circadian rhythms, and many other fundamental physiological aspects. Using multiple LEDs, it is possible to create lights that differ in the amount that they stimulate melanopsin but do not differ in their appearance. These are called metamers and demonstrate how non-visual properties of light can be modulated independently of visual appearance.

The problem with non-linearity of real light sources

Metamers for a light source with multiple LEDs can be accurately characterised to activate the desired photoreceptor given any set of input intensity values for each LED. However, where light sources are non-linear and exhibit spectral shifts as a function of input intensity, it is non-trivial to construct metamers and inaccuracies will necessarily result, leading to problems such as undesired colour distortions.

Novel methods to generate metamers using an algorithm

Researchers at the University of Oxford have developed a novel method to generate metamers with non-linear light sources using an algorithm which incorporates spectral shifts in real light sources. Using a predicted output spectrum, the melanopsin signal and cone signal, for example, can be optimised such that specific spectral properties are achieved. This may include no difference in cone signal between two spectra, and a maximal difference in melanopsin.

The method can be used to make biologically inspired spectra to maximally or minimally stimulate melanopsin, thereby modulating the alertness of an individual, or cause differences in circadian or sleep-related outputs, such as melatonin suppression. Other applications include optimising for a specific Colour Rendering Index (CRI), or other colour rendition metrics.

The main advantages of this method are:

  • Precise light control with multiple non-linear light sources, such as LEDs
  • Generation of calibrated light spectra from a low number of calibration measurements
  • Useful for all settings in which the spectrum of a multi-primary light source needs to be controlled, such as biologically inspired solutions or light therapy

A patent application has been filed on this technology. Oxford University Innovation is interested in talking to potential partners for the commercialisation of this new method.

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