What temperature is it at your location at the vehicle? What pressure did you set the tires to? Have you had any recent tire work done or tire rotations?
You have one of two things going on either whoever installed the tires damaged one of the tire pressure warning sensors that are located inside the tires which is part of the valve stem assembly itself or the system was never properly initialized by using the initialization switch to the left of the steering column depending on whether you have a main set or second set of tires selected. If you consult your owner's manual it will give you more detail on this procedure. Once the system has reinitialize so that the warning light flashes three times and goes out it may take three or four minutes for all of the tire valves to register their ID codes back to the computer and the proper temperature and pressures set at. If the light still does not go out then you're going to have to have a scan tool hooked to the system to determine which sensor is failing.
Should I select the main set or second set if new sets of tires were installed? What are my options if the tire pressure warning sensors are damaged? Where can I go to have a scan tool hooked to the system to determine which sensor is failing and what is a ballpark figure to fix the sensor if its broken? Is it still safe to drive the car if all the tire pressure is correct and the low tire pressure light is still on?
The sensors from the factory are programed to the main set unless you added an additional or second set. The main set side of the reinitialization switch is what you would need to do. If the sensor is damaged the tire will have to be broken down and the sensor replaced. If this was done at a Lexus dealer they should be held responsible to replace the sensor and reprogram. You will need to go to a Lexus dealer. Only a Lexus proprietary software program will interface with the tire pressure warning computer. There are some tire shops that have radio frequency receivers that will be able to identify which transmitters are not functioning but they are few and far between because the equipment is expensive. As far as being safe to drive provided the temperature and pressures are as you stated the only thing this system does is monitor tire pressure. The vehicle will be safe to drive.
You are welcome.