  Both the static $(SLS) $ and dynamic $(DLS) $ light scattering techniques are
used to obtain the size information from the scattered intensity, but the
static radius $R_{s}$ and the apparent hydrodynamic radius $R_{h,app}$ are
different. In this paper, the relationship between SLS and DLS is discussed
using dilute water dispersions of two different homogenous spherical particles,
polystyrene latexes and poly($N$-isopropylacrylamide) microgels, with a simple
assumption that the hydrodynamic radius $R_{h}$ is in proportion to the static
radius $R_{s}$, when Rayleigh-Gans-Debye approximation is valid. With the
assistance of the simulated data, the apparent hydrodynamic radius $R_{h,app}$
has been discussed. The results show that the apparent hydrodynamic radius is
different with the mean hydrodynamic radius of particles and is a composite
size obtained from averaging the term $\exp (-q^{2}D\tau) $ in the static size
distribution $G(R_{s}) $ with the weight $R_{s}^{6}P(q,R_{s}) $.
