I have had a Sony 41" projection TV for about 7 years and it is still working perfectly. For two lights to go after only 18 months is unreasonable & unacceptable. An expensive item like this should last more than that.
I would complain strongly to Toshiba:
Toshiba European Service Centre
Camberley, Surrey, GU15 3DT
Phone: 01276 694000
Fax: 01276 600521