Light's Criteria for Exudative Effusions is a diagnostic tool used in the evaluation of pleural effusions. This calculator is applicable to patients presenting with pleural effusion, a condition characterized by the abnormal accumulation of fluid in the pleural space. The primary clinical utility of Light's Criteria is to differentiate between exudative and transudative pleural effusions, which is crucial in determining the underlying cause of the effusion and guiding subsequent management strategies. 

The criteria include three parameters: the ratio of pleural fluid protein to serum protein, the ratio of pleural fluid LDH to serum LDH, and the absolute value of pleural fluid LDH. An effusion is classified as exudative if one or more of the following conditions are met: the pleural fluid to serum protein ratio is greater than 0.5, the pleural fluid to serum LDH ratio is greater than 0.6, or the pleural fluid LDH exceeds two-thirds of the upper limit of normal serum LDH.