Van Albada and Lagendijk observed weak localization of light in a random medium. In a highly concentrated suspension of polystyrene particles in water, they found polarization-dependent enhanced backscattering of laser light within a cone of approximately 0.2° (half angle) for the highest concentration. This phenomenon, known as weak localization, is a precursor to strong localization and involves enhanced backscattering in a strongly scattering random medium. The concept of Anderson localization, which is the localization of waves due to randomness, is a key concept in physics. It was first described for electrons by Abrahams et al., and related effects for electromagnetic waves have been discussed but not associated with localization. The authors used a suspension of polystyrene spheres in water to study light localization. The suspension had a low absorption coefficient, high concentration (up to 30 vol%), and known single-scattering properties. The high concentration was necessary to reduce the mean free path of light to its wavelength, which is necessary to induce localization effects. The authors observed polarization-dependent weak localization of light in a small cone in concentrated suspensions. They found that the enhancement factors were substantially lower than 2 for their suspensions. The size of the cone was in good agreement with a theory using a renormalized multiple-scattering expansion. The experimental setup involved a He-Ne laser, beam splitter, and detector. The backscattered light was measured as a function of the angle of scattering. The authors found that the backscattered light outside the region of the cone was completely depolarized, whereas inside this region some polarization remained. They calculated some single-scattering properties of the spheres and found that the scattering efficiency was 2.89. They calculated the scattering mean free path of the suspension for light having a wavelength of 633 nm to be 2.6 μm. The average ⟨cosθ⟩ was 0.93, which can be used to calculate the transport mean free path l. The authors found that their results were in qualitative agreement with predictions. The observed parallel enhancement was considerably larger than the observed perpendicular enhancement. However, the enhancement factor for the parallel component was about 1.6 and thus smaller than the predicted factor of 2, while the observed enhancement of the perpendicular component of about 1.3 was larger than the predicted factor of 1. The authors do not have an interpretation of the quantitative difference between theory and experiment yet. They suggest that several different classes of light paths contribute, for instance, short and long paths. More theoretical work is needed before definitive statements can be made. The occurrence of light-localization effects is probably a general phenomenon in many more random materials. The authors hope that their findings will stimulate new theoretical and experimental work.Van Albada and Lagendijk observed weak localization of light in a random medium. In a highly concentrated suspension of polystyrene particles in water, they found polarization-dependent enhanced backscattering of laser light within a cone of approximately 0.2° (half angle) for the highest concentration. This phenomenon, known as weak localization, is a precursor to strong localization and involves enhanced backscattering in a strongly scattering random medium. The concept of Anderson localization, which is the localization of waves due to randomness, is a key concept in physics. It was first described for electrons by Abrahams et al., and related effects for electromagnetic waves have been discussed but not associated with localization. The authors used a suspension of polystyrene spheres in water to study light localization. The suspension had a low absorption coefficient, high concentration (up to 30 vol%), and known single-scattering properties. The high concentration was necessary to reduce the mean free path of light to its wavelength, which is necessary to induce localization effects. The authors observed polarization-dependent weak localization of light in a small cone in concentrated suspensions. They found that the enhancement factors were substantially lower than 2 for their suspensions. The size of the cone was in good agreement with a theory using a renormalized multiple-scattering expansion. The experimental setup involved a He-Ne laser, beam splitter, and detector. The backscattered light was measured as a function of the angle of scattering. The authors found that the backscattered light outside the region of the cone was completely depolarized, whereas inside this region some polarization remained. They calculated some single-scattering properties of the spheres and found that the scattering efficiency was 2.89. They calculated the scattering mean free path of the suspension for light having a wavelength of 633 nm to be 2.6 μm. The average ⟨cosθ⟩ was 0.93, which can be used to calculate the transport mean free path l. The authors found that their results were in qualitative agreement with predictions. The observed parallel enhancement was considerably larger than the observed perpendicular enhancement. However, the enhancement factor for the parallel component was about 1.6 and thus smaller than the predicted factor of 2, while the observed enhancement of the perpendicular component of about 1.3 was larger than the predicted factor of 1. The authors do not have an interpretation of the quantitative difference between theory and experiment yet. They suggest that several different classes of light paths contribute, for instance, short and long paths. More theoretical work is needed before definitive statements can be made. The occurrence of light-localization effects is probably a general phenomenon in many more random materials. The authors hope that their findings will stimulate new theoretical and experimental work.