If l_x is the no. of persons living at the age x and L_x the number of persons living between ages x…

In a life table, $l_x$ is the number of persons living at exact age $x$ and $L_x$ is the number of persons living between ages $x$ and $x + 1$. Under the uniform distribution of deaths across the age interval $(x, x + 1)$, $L_x = \frac{1}{2}(l_x + l_{x+1})$.