Rayleigh scattering is defined by a mathematical formula that requires the light-scattering particles to be far smaller than the wavelength of the light. For a dispersion of particles to qualify for the Rayleigh formula, the particle sizes need to be below roughly 40 nanometres (for visible light), and the particles may be individual molecules. Colloidal particles are bigger and are in the rough vicinity of the size of a wavelength of light. Tyndall scattering, i.e. colloidal particle scattering, is much more intense than Rayleigh scattering due to the bigger particle sizes involved. The importance of the particle size factor for intensity can be seen in the large exponent it has in the mathematical statement of the intensity of Rayleigh scattering. If the colloid particles are spheroid, Tyndall scattering can be mathematically analyzed in terms of Mie theory, which admits particle sizes in the rough vicinity of the wavelength of light. Light scattering by particles of complex shape are described by the T-matrix method.