Maintaining adequate temperature in the glass tank of your Blue Tongues Skink is important because the lighting will directly help maintain proper temperature in the glass tank that is crucial for the survival of the reptile. Lighting is also very important for the reptile to bask in it and is a great way to simulate the light of the sun on the reptile which is something that they not only need but love.
The reason why you should not depend on the natural light of the sun is because the light and temperature from the sun can fluctuate widely especially if it is coming through a glass window. A heat lamp on the other hand, can help you control and maintain the direct temperatures in the tank to as low or high as you want. The diameter of the heat lamp you get should be no smaller than 10 inches because this will give you the flexibility of increasing or decreasing the light impact in the tank enclosure of the reptile.
For the first couple of days, you will have to experiment with the heat lamp before you find out the exact temperature that the reptile prefers. If the animal is spending all its time in the basking area of the enclosure than maybe, the heat of the lamp is not enough and you have to increase the settings or get a stronger bulb. But if the lizard is spending too much time in the cooler end of the enclosure or the water pool then chances are that the heat in the tank is too much for the animal and you have to tone down the heat settings of the lamp.
A heat lamp is not an expensive item to purchase for your skink reptile and it will be easily available from any pet store around you. A good heat lamp will be as cheap as $10-15 especially those with a 10-inch diameter. Obviously, if your glass tank is larger than a typical blue tongue skink glass tank or if you are keeping two reptiles in one large tank, then you will have to get a larger heat lamp and a bulb of greater strength, 120 watts or more.
During the night time, you can switch the lamp off for about ten to twelve hours but at no point should the temperature in the tank fall below 60 degrees so if your house is extraordinarily cold, you might want to get an under the tank heater to keep the glass tank of the skink warm enough.