Particle distributions in the Indian Ocean have been studied by means of light scattering observations made through 45° on collected water samples. Since a rough relationship exists between primary production, stock of phytoplankton and total amount of particles such observations are indicative of oceanic productivity. Thus an abundance of particulate matter is found at the fertile divergence zone associated with the boundary at 8°-9''S between the South Equatorial Current and the Counter current. Several series of measurements in the Indian Ocean and the Red Sea show that the penetration of radiant energy (from sun and sky) in areas of high productivity is less effective than it is in areas which are poor in' particles. A newly developed quanta meter is briefly described. This meter records number of quanta in the sjsectral range of 350-700 nm which is photo synthetically active. A method is presented which allows of converting simple underwater observations of blue light into quanta within the range mentioned.