Hello. I came across a secondhand Thunderbolt display recently, but when I tested it it seems quite dark. It was connected for testing to a 21.5-inch iMac retina, and the difference was quite palpable. I know retina screens are supposed to be bright, but the difference seemed like 50% brightness. At full brightness the Thunderbolt display seemed only as bright as the retina iMac at normal/half brightness. Is this normal? A byproduct of old age? I've looked at demo Thunderbolt displays in retailers before and the brightness seemed okay. Any other potential problems I should be aware of? Appreciate any advice. Thanks guys!