In KEY 4 you'll explore which colors of light to embrace at night to promote deep rejuvenating sleep and which colors of light to embrace during the day to promote energy and focus.
Blue Blocker Glasses:
My best advice is to conduct a search on eBay for "HIGH CONTRAST BLUE BLOCK GLASSES. I personally love the AVIATOR STYLE. Most of the vendors sell similar glasses. The high contrast lens usually offer you better visibility and cost under $10.