Blue tongue skinks should be maintained in the mid 80's during the day, and temperatures can safely drop into the upper 70's at night. During normal daylight hours, a localized basking spot should be present at one end of the cage. Basking temperatures in this area should be between 90 and 95 degrees.
Heat may be provided during the day with standard basking bulbs, ceramic heat emitters, and under tank heating pads. Heating pads and other non-light heat sources can be used at night to keep temperatures within the recommended range. In large enclosures, mercury vapor bulbs which not only provide ample heat, but full spectrum light as well, can be utilized. Mercury vapor bulbs are one of the most popular and easy to use methods of providing heat and UVB lighting in the most convenient way possible.
Some advanced keepers are able to maintain blue tongue skinks without full spectrum lighting. However, by doing so, the chances of metabolic disorders increases greatly, especially when raising young animals. Thus, full spectrum UVB light is highly recommended for this species.
You can provide this type of light (which the animals would receive from the sun in the wild) with specially designed fluorescent bulbs designed specifically for providing UVB light to reptiles. Or, as mentioned above, mercury vapor heat/UV bulbs can be used in larger enclosures. Exposure to these wavelengths of light will allow your lizards to properly synthesize vitamin D3 and metabolize dietary calcium