Study on Safety, Feasibility and Neural Activation of Non-Invasive Light Therapy System

Inclusion Criteria: * Adult competent persons able to understand the nature of the study and give written informed consent. * Stage I: Healthy elderly subject. * Stage II: Diagnosed with probable mild to moderate AD based on NIA-AA diagnostic criteria. * Age \>55 years and \<80 years. Females must be post-menopausal. * Fluent in Danish * \> 8 year of normal school education * Pass a colour-blindness test (Ishihara colour test) * Have visual and auditory capabilities, and language skills necessary for neuropsychological testing. * Furthermore, subjects must have a person, hereafter named designated caregiver, who is available to the participant and can provide the necessary assistance with using the LTS device and Actigraph wearable at home and can assist with clinic visits and other practical issues. Exclusion Criteria: * Profound visual impairment provided correction with spectacles, if needed. * Significant abnormalities related to important parts of the brain e.g. the visual system, pre-frontal cortex or hippocampus, or relevant lesions detected by MRI. * Prior history of significant diseases related to the visual system or the brain. * Medication Any patient using antiepileptic drugs, neuromodulating drugs or high dose of sedatives will be excluded. * Prior history of substance abuse within the past 2 years. * Any significant systemic illness or unstable medical condition, which could lead to difficulty complying with the protocol.