Abstract: The light absorption and adsorption properties of three cyanine dyes Ⅰ, Ⅱ and Ⅲ were studied in solution and in their adsorbed states for each dye alone and for their combinations.Adsorption isotherms of dyes to suspended AgBr at 25℃ and the absorption (reflection) spectra of dyes in solutions and in adsorbed states were obtained. Very small heat effects (< 10 mcal) accompanying dye adsorption were measured with the Versatile Model BD-1 Precision Semiconductor Calorimetric System developed by us using a calorimetric unit specially designed for this adsorption system. The precision temperature control of the thermostat to 25±0.0001℃ was implemented by a microcomputer system. The isosteric molar enthalpy of I adsorption to AgBr in water was obtained to be - (33.5±2.5) kJ/mol (Surface coverage 0000=94%). Also from dye combination studies, the obtained spectra, isotherms as well as appreciable heat of adsorption all indicate further adsorption of dye Ⅰ to AgBr dyed with Ⅱ and/or Ⅲ, forming possibly multilayers over the first layer of Ⅱ and/or Ⅲ, while no (or very little) adsorption of Ⅲ and/or Ⅲ can take place over dye Ⅰ. This clarifies the fact that in the photographic emulsion production, the green sensitive dyes Ⅱ and Ⅲ must foe added prior to the adding of I to ensure supersensitization. The results show that enthalpy measurements in combination with spectrascopy may be helpful for studying the sensitizing effect in photographic emulsion production.