assuming the range of light covers the entire animal when up close, yes. Otherwise you need more lights.The cage sounds like its in the ballpark...
Not sure what you mean by large lamp? but using spotlights instead of floodlights can cause burns on monitor lizards,
Its best to use lower wattage (45watt to 75watt) halogen/incandescant, flood light type bulbs and get them close to the animal.
Higher wattage bulbs that are placed further away from the basking spot, tend to dry out the air in the cage to much, which is not one the goals if you keep monitors.