In The European Union as well as in Switzerland the legal defaults for the illumination intensity in animal stables are indicated in the unit "Lux". This however is an unsuitable unit because it reflects the brightness perceived by humans. Animals have specific spectral sensitivities, their brightness perception differs from that of humans. That leads to the fact that the stables are lit up not in the minimal brightness intended by the legislator, but either too bright or too dark, depending on the animal specie and the used source of light. The proposed project aims at establishing an exact sensitivity curve for poultry with the help of the methodology of Operant Conditioning. This serves then as a reliable basis to accurately determine the brightness actually perceived by poultry. Later on the developed methodology and equipment may also be used, after certain adjustments, for the determination of the sensitivity curves of cattle and pigs or other farm animals.