It’s a sad thing to watch a screen degrade. The first thing you may notice in your dying screen is that the brightness isn’t what it once was. Displays rely on backlights which can degrade over time and lose their brightness. You may start noticing dead or hot pixels, which can show up as bright, single-color pixels that stand out from what should be on the screen. Older monitors also sometimes suffer from burn-in. This involves on-screen objects leaving ghostly images of themselves after staying on the screen for too long. The TVs at your local gym likely have this from the tickers that run across the bottom of the TV news channels.