Scalar or vector light of wavelength 2 π/k strikes N small refracting and absorbing spherules, each of radius a , which have coagulated into a sparse random cluster with fractal dimension D (for smoke, D ≈1·78). It is assumed that ka Π1 but the cluster size R = aN 1/D may be larger than the wavelength. Using a mean field theory it is shown that multiple scattering is negligible for all N if D < 2, and becomes important when N ~ (ka) -D/(D -2) if D > 2. Cross-sections are calculated as functions of N , D and the complex refractive index of the spherules. If D < 2 the scattering cross-section per spherule rises with N and saturates when kR >>1, at a value exceeding that of an isolated spherule by a factor of order ( ka ) -D ; if D > 2 the same quantity increases as N 1 -2/D /(ka) 2 . For D < 2 the absorption cross-section is N times that of a solitary spherule. These results are very different from those for spherules coagulating into compact solid spheres ( D = 3), and are important for the optics of sooty smoke, with D ≈1·78, which is used as an example throughout.