Alzheimer's disease (AD) not only takes an emotional toll on the individual with the disease, their families, relatives, and caretakers, it also has immense socioeconomic consequences on the health care system and society. Moreover, the socioeconomic consequences are expected to increase significantly, thus reducing the social and economic cost of AD is of high importance. Recently, exposure to 40 Hz stroboscopic light therapy, for one hour a day, resulted in slowing the progression of AD in

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... e and has a considerable potential for treatment in humans. However, exposure to such stroboscopic light carries its own consequences being that it is difficult to implement in a patient's daily routine, irksome to use, and can cause visual discomfort which may result in a lack of patient adherence. Here, we demonstrate a novel technology based on controlling multiple single-color LEDs to produce white light where its spectral composition alternates at a given modulation frequency without visible flicker. We coin this technique as Invisible Spectral Flicker (ISF). We present 40 Hz invisible spectral flicker light as a potential alternative in reducing discomfort compared to 40 Hz stroboscopic light, whilst still entraining oscillations in various areas of the brain. Furthermore, we demonstrate a distinct way to generate a 40 Hz metameric light source with the presented color mixing scheme, and validate that the CIE 1931 (x, y) coordinates match for two different spectral power distributions. Finally, we illustrate the light characteristics of seven 40 Hz color fusion light sources and two 40 Hz stroboscopic light sources. The technology presented here will lead to new, and hopefully improved, designs of light therapy systems for the treatment of Alzheimer's and dementia.