LG 42LM620T 3D LED LCD TV Review

Benchmark Test Results

Dead pixels None
Screen uniformity Good for an LCD TV, mild lighter patch at top left
Overscanning on HDMI 0% with Aspect Ratio set to “Just Scan”
Blacker than black Passed
Calibrated black level (black screen) 0.04 cd/m2 (lights dim)
Calibrated black level (ANSI checkerboard) 0.163 cd/m2
Black level retention Subtly implemented undefeatable backlight dimming causes dark scenes to appear dimmed
Primary chromaticity Good
Scaling Excellent
Video mode deinterlacing Very effective jaggies reduction
Film mode deinterlacing Passed 2-2 PAL and 3-2 NTSC tests
Viewing angle Very Good for an LCD TV; colours remain largely saturated but blacks brighten
Motion resolution 300 lines
Digital noise reduction Very mild undefeatable grain smoothing, difficult to spot without comparison
Sharpness Defeatable edge enhancement
Luma/Chroma bandwidth (2D Blu-ray) Full Luma, Chroma horizontally blurred unless 60hz input signal and “PC” input label selected
1080p/24 capability No judder in 2D or 3D, provided [Real Cinema] enabled
Input lag 31ms compared to lag-free CRT
Full 4:4:4 reproduction (PC) Yes, with input label set to “PC” (bypasses some calibration controls)

Power Consumption

Default [Standard] mode (2D) 57 watts
Default [Standard] mode (3D) 60 watts
Calibrated [ISF Expert1] mode (2D) 46 watts
Calibrated [ISF Expert1] mode (3D) 43 watts
Standby 1 watt

Picture Quality

Black Level

We always start reviews of IPS displays in the same way… by reminding users not to expect deep blacks from them. It’s a pity that these panels are black-impaired, because compared to the LCD competition, they get pretty much everything else right.

We already noted the LG 42LM620T‘s auto-dimming behaviour, so weren’t surprised to see that with a black screen, the panel managed a minimum luminance level of 0.04 cd/m2. Normally we’d warn users that this sort of black performance won’t be applicable with real-world content, but in this case, it actually is. Of course, an IPS panel with this black level performance is too good to be true – it’s achieved by dimming the light sources, so although you get very dark blacks during dark scenes, you also get very dark whites. The contrast performance with predominantly dark scenes is still mediocre, but in a new way.

An ANSI checkerboard chart – which splits the screen into equal black and white boxes, like a chess board – reveals the unassisted black level performance. With [Backlight] set so that peak white output is at around 120 cd/m2, the black patches measured 0.16 cd/m2. That’s fairly consistent with other IPS-based LCD TVs we’ve reviewed lately – the higher-end LG 47LM960V measured at 0.17 cd/m2 with its local dimming options shut off, and Panasonic’s TX-L42ET50 also managed 0.16 cd/m2.

One other thing we did during calibration to ensure the best black level possible was to raise the [Contrast] control, since on an LCD TV, this is one of two controls which affects light output. This is an often overlooked point. For once, it’s set too LOW out of the box on the 42LM620T. We adjusted it upwards to just before the point where the television begins to crush the rarely-used whiter-than-white shades out of the image. Setting white level/contrast as high as possible is critically important on a display featuring an LCD panel type known for mediocre black level performance. We align each HDTV we review to produce a peak white output of 120 cd/m2, and it’s important to achieve as much of this as possible with the digital white level control to maximise the contrast performance of the panel. This means that the [Backlight] control can be set lower to hit our brightness target, which in turn, will result in better black levels (raising the Backlight brightness to achieve our 120 cd/m2 target will result in a brighter image, but that means brighter blacks as well).

Motion Resolution

The LG LM620T doesn’t feature a 100hz or 200hz-capable LCD panel, so unsurprisingly, it managed only about 300 lines out of a possible 1080 in the horizontally scrolling motion tesolution test from the FPD Benchmark Software disc. The black text on the grey background also displayed with white ghost images (overdrive errors).

Don’t be fooled by the fact that the 42LM620 features several [TruMotion] motion interpolation modes: the panel isn’t capable of any higher level of motion clarity, so enabling this option will only give films a “soap opera effect”, and do nothing to improve motion clarity with high motion video content (such as TV sports).

The good news though is that the panel fitted to the LG 42LM620T has no significant motion issues beyond the blur you’d expect with an LCD TV (and beyond the slight overdrive errors we just mentioned). For example, in the FPD Benchmark disc’s “Hammock” clip, we observed very obvious low-tone smearing on the last similarly-priced budget LCD television (the Samsung ES5500) we reviewed: the girl’s face would be covered with blue trails. There’s nothing like that to be found on the LM620T, a feat almost certainly owed to the usage of the IPS LCD panel.

For a non-100hz/200hz LCD TV, the LG 42LM620 exhibited very good motion performance. It obviously pales in comparison to the faster LCDs, and especially Plasma TVs, though.

High Definition

After reviewing the high-end LG LM960V, we were a little anxious to see what the LM620 would do when fed with high quality material from Blu-ray. The aforementioned flagship LED TV had fairly noticeable noise reduction processing (even with the NR controls in the menu shut off), and this processing caused the amount of film grain texture to vary distractingly: a shot could start with grain visible (as is correct for film material), but only a few seconds later the television’s processing would kick in, causing the film to appear smoothed-over, less detailed, and video-like. As it turns out, the cheaper model doesn’t seem to leave the image entirely untouched, with grain being lightly smoothed over at certain luminance levels. For example, at 35 minutes into Taxi Driver (the scene outside the cinema), the background grain on the 42LM620T looked like it was only updating every second frame, appearing with a slight “crawling” effect. But to confirm this, we had to watch content we were very, very familiar with, side-by-side with another reference: the issue is more subtle than it is on Samsung’s current LCDs.

Babel screenshot

Speaking of film, we were very happy to see the LG render 24p motion without any unwanted judder or interpolation – providing very cinema-like motion. Just be sure that you have [TruMotion] OFF and the [Real Cinema] mode on to get this motion quality, though. Although the LCD panel can’t produce blur-free motion with high-motion video content, the lower frame rate of film (24fps) doesn’t pose any problems for the 42LM620T’s panel.

In fact, we did a side-by-side comparison with the Panasonic TX-P50ST50 Plasma, which we consider to be the flat-screen TV to beat in its midrange price point (in fact, we consider it to be a display to beat even at higher price points thanks to its near-perfect colour reproduction). The 42LM620 is around £200 cheaper at the time of writing, however. The LG’s superior greyscale tracking (we’re talking about after calibration with the 20-point control, but it also applies before) provided more accurate grey shades, but its less accurate colours were visible in the comparison, especially with blue shades. During the outdoor space shots in Aliens, for example, a display with better colour reproduction renders the clouds blue, whereas the LG instead showed a purple-ish colour. Films which have been coloured in teal and orange (think nearly any modern Hollywood action film) appear more “purple and orange” on the LG LM620T. We didn’t feel that this substantially changed the feeling of the content we were watching, but it’s an inaccuracy all the same. Some animated content also appeared slightly dulled due to the panel’s inability to satisfy the Rec.709 HDTV colour gamut.

Daytime viewing is where LCD technology can really shine. Compared to Plasma televisions (including those with ambient light filters coating the screen), black levels are better retained during the sunny hours. Unfortunately, because of the LG 42LM620T’s behaviour with dark scenes which we discussed earlier, these details can be harder to see in a bright room, because the screen dims. Self-emitting displays (currently, that means Plasmas, and in the future will also mean OLED TVs as well) don’t have this problem, since the light output of each pixel can be individually controlled.

The opposite is true when it comes to nighttime viewing, though: in a dark room, the mediocre black levels of IPS LCD panels has no ambient light to hide in. When we dimmed the lights and watched dark scenes from Taxi Driver, the Panasonic ST50 Plasma almost disappeared into the darkness, whereas the LG LM620 LCD only managed a dark-grey glow (with a brighter spot in the top left corner) – even with its dimming trick. However, the Panasonic ST50 had the tendency to tint the shadowed areas mildly red, owed to its less accurate Greyscale tracking and lack of any controls to correct this – the LG LM620T has more linear greyscale tracking to start with, AND 20-point controls to correct the small errors – the ST50′s is less linear and only has a 2-point correction menu.

Babel screenshot 2

All in all, we were happy with the HD picture quality from the 42LM620T. We know by now not to expect deep blacks from IPS LCD panels, and provided prospective buyers know this, we doubt anyone will be disappointed with the picture quality.

Standard Definition

The 42LM620 handled SD content very well, doing a great job at avoiding drawing jaggies during the deinterlacing process. It also correctly identified the 2-2 film transfer cadence and displayed full vertical resolution with no jaggies for films transferred to the PAL TV system. It even managed to pull this off with old analogue telecine material that’s been transferred out-of-phase, which almost never appears on TV or DVD!

Not only does it display every last drop of detail from standard-def images, thanks to its excellent scaling algorithm, but it also seems to be performing a secondary anti-aliasing step to hide static jagged edges. Very impressive.

Simply put, we don’t think the LG 42LM620T’s SD-to-HD upscaling processing could be any better.

3D

As a passive 3D TV, we knew from the start that the LG LM620T wouldn’t be able to display extra-dimensional images with full vertical resolution. We got a shock, though, when we checked out some 3D test patterns on the display and saw plenty of pixellated edges on show. Not only were the fine horizontal lines (which act as a check for vertical resolution) totally invisible – they were blurred into a solid grey smudge – but the fine pixel-thin details appeared with a severe amount of aliasing around edges. On the higher-end LG LM960V 3D television we reviewed, we noticed that the set was vertically blurring images in 3D mode, presumably to prevent aliasing when the image was viewed through the passive 3D glasses. We’re not sure what’s going on with the 620T; all we know is that the three-dimensional video processing is, well, botched.

Ironically enough, this was much less visible once we put the polarized 3D glasses on, because the thick black lines which become visible over the image mask the problem. In other words, because a passive 3D panel isn’t capable of full resolution anyway, the underlying blockiness being caused in the video processing stage was less visible.

Now the resolution caveat is out the way, comes the good news: passive 3D gets absolutely everything else right. We could watch tri-dimensional content for hours on end without any of the fatigue often associated with the flicker of the active system’s glasses. Once we’d calibrated the 3D mode through the glasses, greyscale and colour accuracy were just as good as it was in 2D, which is a real feast for the eyes. And, as we expected from a passive 3-D television, the LG 42LM620T had no issues with displaying judder-free motion with any frame rate: 50hz, 60hz and 24hz input all displayed judder-free (be sure to have [Real Cinema] enabled for the latter, though).

LG has a lot to be proud of with its championing of the passive system, because if you can see past the fact that you’re getting a half-vertical-resolution image which has black lines visible over it, then it’s smooth sailing from that point on. As video lovers, both active and passive 3D leave us unsatisfied, because they both have their issues. Which set of faults is more tolerable will be down to the individual.

Console Gaming

Gaming was great fun on the LG LM620T, with a very respectable 31ms of input lag being the only thing standing between us and the game. There is a “Game” picture preset, but the best results came from labelling the HDMI input as “PC”, which unlocked full 4:4:4 chroma resolution. We could then use our calibrated [ISF Expert1] mode for gaming. In the PC mode, this keeps the 20 point Greyscale corrections active, but doesn’t allow the use of the colour management system (at least not with our PC’s RGB signal). Excellent performance.

Conclusion

The LG 42LM620T is an imperfect, but nevertheless decent LED LCD TV. Happily at this price point, it doesn’t have any significant picture quality issues beyond the inherent limitations of its mediocre black level (unavoidable with IPS-type LCD panels) and the lessened 3D resolution (par for the course with passive 3D). Colour reproduction could also be better, with the LM620T failing to reproduce the most saturated extremes of the Rec.709 HDTV colour standard, something we often see with LED-lit LCDs. On the up side, we were very happy to see that nearly none of the video processing issues we discovered on the company’s more expensive LM960V were present on this mid-range model.

Our final recommendation of the 42LM620 is more or less the same as with other IPS LED LCD televisions, such as the Panasonic TX-L42ET50 – if you plan on installing it in a bright room where the weak IPS black level won’t be an issue, then it’s a good choice. The Panasonic is slightly more expensive, provides a better 3D experience (thanks to its full resolution images, which also avoid the blocky video processing issues of the LG) and has better colour accuracy, whereas the LG is more affordable and will interest those who prefer the passive 3D system. Few aspects of its picture quality are perfect (calibrated greyscale accuracy being the exception), but we don’t think it has any significant faults, either.

In the end, we felt that the LG 42LM620T managed to pull itself into “Recommended” territory. It has issues which buyers should be aware of, but it can produce images which are worthy of inclusion in this category.

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