Brian & Tom -- These would be very good answers if the MacBook Pro 15 Unibody 2.53 GHz Mid 2009 used a LCD or an inverter. The LED backlighting doesnt have an inverter like the ccfl backlight does (this is one of the advantages of led technology).
15.4" color widescreen LED-backlit TFT active-matrix "glossy" display with a 1440 by 900 native resolution. Apple heralded this display as providing "60% greater color gamut" than the earlier "Unibody" MacBook Pro models that this system replaced. By default, the display is "glossy", but starting on August 11, 2009, Apple also began offering this model configured with an "anti-glare" (matte) display for US$50 more.
inverter.....or loose connection.....
tap the display frame lightly, or tilt the display back and forth and see if the backlight comes on, if it does only briefly it might just be a loose cable connection. Testing of the inverter should still be done once it is taken apart.
I am guessing it is no longer under warranty? (since your asking the question).