We study the extinction efficiencies as well as scattering properties of particles of different porosity .
Calculations are performed for porous pseudospheres with small size ( Rayleigh ) inclusions using the discrete dipole approximation .
Five refractive indices of materials covering the range from 1.20 + 0.00 i to 1.75 + 0.58 i were selected .
They correspond to biological particles , dirty ice , silicate , amorphous carbon and soot in the visual part of spectrum .
We attempt to describe the optical properties of such particles using Lorenz-Mie theory and a refractive index found from some effective medium theory ( EMT ) assuming the particle is homogeneous .
We refer to this as the effective model .

It is found that the deviations are minimal when utilizing the EMT based on the Bruggeman mixing rule .
Usually the deviations in extinction factor do not exceed \sim 5 \% for particle porosity { \cal P } = 0 - 0.9 and size parameters { { { { x _ { porous } = 2 \pi r _ { s, porous } / \lambda \mathrel { \mathchoice { \vbox { % \offinterlineskip \halign { \cr } $ \displaystyle < $ \cr$ \displaystyle \sim$ } } } { \vbox { % \offinterlineskip \halign { \cr } $ \textstyle < $ \cr$ \textstyle \sim$ } } } { \vbox { % \offinterlineskip \halign { \cr } $ \scriptstyle < $ \cr$ \scriptstyle \sim$ } } } { \vbox { % \offinterlineskip \halign { \cr } $ \scriptscriptstyle < $ \cr$ \scriptscriptstyle \sim$ } % } } } 25 .
The deviations are larger for scattering and absorption efficiencies and smaller for particle albedo and asymmetry parameter .
Our calculations made for spheroids confirm these conclusions .
Preliminary consideration shows that the effective model represents the intensity and polarization of radiation scattered by fluffy aggregates quite well .
Thus , the effective models of spherical and non-spherical particles can be used to significantly simplify computations of the optical properties of aggregates containing only Rayleigh inclusions .