In order to evaluate the use of vegetative growth models, crop water requirements, agricultural zoning, and many other applications, it is important to know the long wave radiation budget (> 2800 nm). The BRUNT-GEIGER equation is very well known and used and it was obtained for climatic conditions of Germany (RLO = sT4 (0.56 - 0.09.e0.5 ).(0.l + +0.9 n/N)). ROBINSON (1966) saliented that the reflected fraction from cloud base affects the budget of this spectral band. The albedo depends on cloud thickness, and this pattern is different for each kind of cloud. In the present work, with data collected during one year with net radiometers, Eppley pyrheliometer and heliograph by OMETTO (1968), at the Piracicaba region (22.7 deg S 47.6 deg W, and 570 m of height) one set of equations was adjusted using RLO (long wave radiation, given in cal/cm2.day), e (partial vapor pressure, given in mmHg), air temperature (K), and n/N (insolation ratio), giving: (12) RLO=sT4(0.44-0.056.e0.5).(0.06 + 0,97 n/N) and (14) RLO = sT4(0.233 - 0.056.e0.5+ 0.209.n/N), forthe year; (15) RLO = GT4(0.23 - 0.051.e0.5 + 0.19 n/N) for spring-summer; (16) RLO = sT4(0.23 - 0.062.e0.5 + 0.24 n/N) for autumn-winter, where s is the Stefan-Boltzman constant (1.17 x 10-7 cal/cm2.day). Equation 2, when compared with BRUNT-GEIGER's equation, indicates that the air humidity (e - partial vapor pressure) yields an emissive power lower than the observed. Results