Preferred body temperatures data from Wilson , the Preferred Body Temperature (PBT) for Bearded Dragons is 35 degC (95 degF).
Their Preferred Optimum Temperature Range (POTR the range of temperature needed to maintain normal body functions) is 35 degC to 39 degC ie (95 degF to 102 degF).
Relationships between PBT and ambient temperature from Mumford.
and Behaviours based on ambient temperature from Thompson.
Further information
The Effect of Thermal Quality on the Thermoregulatory Behavior of the Bearded Dragon Pogona vitticeps: Influences of Methodological Assessment. Cadena V, Tattersall GJ (2009)
Physiol Biochem Zool 82: 203–217
In the study most dragons were found to not seek shade (cooling) until around 40c+. As indicated by not only behavior, but a measured increase in hysteresis; the main goal of the study.