A photocell is any of a wide range of sensors that react based on the presence of light or electromagnetic energy. They can be found in many different forms, from solar panels that use light to generate electricity, to photoresistors, which shift in resistance based on how much light is present.
Bond prices and yields are like a seesaw: when bond yields go up, prices go down, and when bond yields go down, prices go up. In other words, a move in the 10-year Treasury yield from 2.2% to 2.6% indicates negative market conditions, while a move from 2.6% to 2.2% indicates positive market performance.
High yield bonds hold the potential for higher returns for two reasons. Higher coupon rates. In general the issuers of high yield bonds are considered less likely to make interest payments than issuers of investment grade corporate debt. Because investors are being asked to assume this risk, high yield bonds tend to come with higher coupon rates, which can generate additional investment income.