Residential swimming pools usually have their own separate circuit running to a GFI recept, through a switch, and then to the pool light. Does it have to be a separate circuit or can I install a new run by tapping to another exhisting circuit to run the pool lights. (Providing the exhisting circuit is not loaded up too much).
This is a repair.

Also, there are 2 lights on this pool.

when you say its fed from a "gfci and through a switch" does it have a step down xfmr? Is this an existing pool light where your adding another light? Is there a panelboard at the site of the pool equipment(if any)? You should definetly see article 680 of the NEC. At present, more information about the conditions are needed. Pool lighting is dangerous business if not installed correctly. If this is a side job you might want to consider passing on it.

Yes, it is an exhisting pool light,
(2 lights) and has a panelboard at the filter where the 1 circuit for the GFI recept for the lights are fed from, (but rusted out and broke underground). It does not need a transformer, they are 120v pool lights.
If I were to tap a circuit for the pool lights, it would be a much shorter run than from the panel. But I may need to do that.

680-6(b)lighting fixtures etc
(2)existing lighting fixtures and lighting outlets located less than 5 ft measured horoizontaly from the inside walls of a pool shall be at least 5 ft above the surface of the maximum water level, shall be rigidly attached to the existing structure, and shall be protected by a groundfault circuit interupter.
(c)switching devices. switching devices on the property shall be located at least 5 ft horizontally from the inside walls of a pool unless separated from the pool by a solid fence, wall, or other permanent barrier.
680-10. underground wiring location. underground wiring shall not be permitted under the pool or within the area extending 5ft horizontally from the inside wall of the pool.

this is only a sampling of the code. it seems that you could use another source other than the panel but there is yet another code in this section which requires no less than a #12 ground wire.
do you have access to a code book? if not i would check with your local library. swiming pools are extremely dangerous places with regards to electricity.

I looked through the code book and couldn't find anything on having to put a pool light on a separate circuit.