LCD backlight off after changing to a new display?

Both screens are the LED backlit models (they are used on the SR/07 model you have and the 2008 model, but are not interchangeable between both). The original one you have is the LG model, and the replacement is an AU Optronics. It is common for a company like apple to outsource manufacturing to multiple manufacturers, because of the quantities they dealt in. (relying on one manufacturer would have been too risky)

The original LCD that you had was the LG model, which is typically used within the 2008 model, not the SR (do you definitely have the A1226 and not the A1260?), and the AUO LCD is also seen most commonly within the 2008 model. if you can confirm your range i can help with identifying the exact model you need... if you have an 08 model, the replacement should work fine, as the different manufacturers are interchangeable, but they are not interchangeable between the 2 years.