Solow-Swan production function- What is '$L$' If $L$ represents the amount of labour in the Solow-Swan production function:

$Y/L$=$f(K/L)$

how can $Y/L$ equal 'per-capita income' if $K/L$ is the capital/labour ratio? 

I thought per-capita income was income divided by the entire population.

Thanks.
$L$ is labor, which is equal to population in Solow-Swan model. Solow did not actually believe the workforce and population had the same size, but what's important is that labor is supposed to be in direct relationship with population i.e. there is a number w between 0 and 1 such that

$L = w *$ population

Direct proportionality between population and workforce is one of the assumptions of the Solow model.