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.
Yield. Yield of a bond fund measures the income received from the underlying bonds held by the fund. The 30-day annualized yield is a standard formula for all bond funds based on the yields of the bonds in the bond fund, averaged over the past 30 days. This figure shows you the yield characteristics of the fund's investments at the end of the 30-day period. It does not indicate the fund's future yield.