I have recently build a new indoor tortoise table and it is much larger than the previous table I had and I am having trouble with the temperatures at the cool end of the table. 

The temperature under their basking light is around 32 degrees. There is a good gradient across the table but I am worried that at the other end the temperature is only around 16/17 degrees. I am not concerned with night temperatures as I know in the wild they are exposed to low night temperatures and the temperature won't fall below 10 degrees in the house.

I don't want to put the heating on more as the current ambient temperature is perfect for us (we live in Scotland so we are used to the cold!) and we will be too hot. 

This current situation means the tortoises only like to spend their time in the warmer half of the table defeating the point in doubling the length of the table.

Has anyone used tubular heaters or ceramic lamps to increase the temperature in the day on their indoor tables?