Travelling by public transport from Faro Airport to Praia da Luz is a bit of a number:
You have four options:
1) Taxi direct from Faro Airport to Praia da Luz
The Summer 2007 officially quoted price (Faro Airport Guide )
is between Euro 79.00 and Euro 120.00. (At this price you are almost better hiring a car)
2) Shuttle Service direct from Faro Airport to Praia da Luz
See the following:
http://www.low-cost-transfers.com/
http://www.polotur.com/
http://www.solpraiaferias.com/index.php?content=transfers&lang_opt=en
Costs circa Euro +-60
3) Bus - Train - Bus
See Cubsur's
www.algarvebus.info
and
http://www.solpraiaferias.com/index.php?content=cheg_en
Essentially you have to take a bus from Faro Airport into Faro Bus Station, then walk to Faro Station. Get a train from Faro to Lagos.
The walk to Lagos Bus station and then get a bus to Praia da Luz.
4)
Bus - Train - Bus
See Cubsur's
www.algarvebus.info
and
http://www.solpraiaferias.com/index.php?content=cheg_en
Essentially you have to take a bus from Faro Airport into Faro Bus Station, then walk to Faro Station. Get a train from Faro to Lagos.
Then walk to Lagos Bus station and then get a bus to Praia da Luz.
4) Bus - Bus - Bus
Again see Cubsur's
www.algarvebus.info
and
http://www.solpraiaferias.com/index.php?content=cheg_en
Essentially you have to take a bus from Faro Airport into Faro Bus Station, then get a bus from Faro to Lagos, (soemtimes via Albufeira). Then another bus to Praia da Luz. Note last daily bus (weekdays) Depts. Lagos 19:15
In summary, unless you flight arrives before 14:00 you will probably find it difficult to get to PDL by bus/train.
Hope this helps!