Not being able to produce a true black also inevitably causes problems for other colour tones during dark scenes, leaving them looking a little off key.
Contributing still further to the Panasonic L55DT50‘s dark scene problems are some fairly noticeable patches of extra brightness in the image’s corners as the illumination system struggles to keep base light levels consistent across the 55in screen.
Reducing brightness doesn't really help
You might think that reducing the image’s brightness setting would instantly improve many of the issues mentioned above. But actually it just makes dark scenes look a deeper shade of grey while simultaneously taking even more shadow detail out of the image. This sort of response to brightness reductions is a sure indication of a screen that doesn’t have a very good core black level response.
It doesn’t help here that, unlike most of its rivals, Panasonic doesn’t offer any form of manual backlight adjustment to accompany the set’s brightness control.
And there’s still more. For during our tests we were quite surprised by just how primitive the set’s dymamic backlight system seemed to be. This is designed to automatically adjust the screen’s illumination levels in response to an ongoing analysis of the image’s content, in a bid to boost black level response. So when the TV detects a shot is predominantly dark, the LEDs will have their output reduced to boost black colours before they’re stoked up again when bright content comes on.
Dynamic backlight system needs work
Such systems are routine in the LCD TV world now, but we were struck during our tests of the Panasonic L55DT50 by a) how distractingly obvious its backlight ‘shifts’ were when watching predominantly dark scenes, and b) how unsophisticated the system seemed to be at determining when to make its backlight adjustments.
A classic example of the dynamic backlight issues that trouble the L55DT50 can be seen in the final Harry Potter film on Blu-ray. At 5min 42secs in, a shot through some stairs downstairs into a light kitchen pans slowly up onto a much darker shot on an upper landing. During this camera move the L55DT50 first looks extremely grey where it should look black, before suddenly and very distractingly shifting its brightness down a number of gears at once as the last chink of light from the downstairs part of the shot finally disappears off the bottom of the screen.
Basically, the L55DT50’s handling of this admittedly tough-to-show shot is a mess - and trust us when we say you don’t have to be an experienced TV reviewer to see the problems.
With this in mind it’s a real shame that Panasonic hasn’t followed the lead of many of its rivals and provided you with some flexibility over how aggressively the dynamic backlight system works. In fact, so far as we could see you can’t even manually elect to turn the system on or off. The only time we noticed that it was inactive was when we selected the True Cinema preset. Unfortunately, though, while this mode meant dark scenes avoided the backlight instability noticeable with other presets, it also failed to deliver anything like the black level depth we would hope to see from a 2012 LED TV.
Much better in ambient light
One oddity about all these black level problems is that if you let a lot of light into your room, especially direct sunlight, the L55DT50’s black level response improves vastly. We would expect this to happen to some extent merely as a result of how the introduction of ambient light alters your perception of the light coming from the TV. But with the L55DT50 the effect seems unusually pronounced, almost as if some contrast filter in the screen actually needs ambient light around before it starts to work properly. Weird.
Even in these relatively bright ambient conditions, though, there’s a problem, as the glassy screen finish proves rather reflective of bright objects in your room.