LG 50PZ950 Plasma HDTV Review

Black Level

People looking for a plasma television are often afficionados of rich and deep black levels. The LG 50PZ950 does not give you that virtually pure black screen you hope to get from plasma technology. A reading of 0.04 cd/m2 is strong, but you can see this on some of the best LCD screens. The two comparable plasma screens in the chart, the Samsung and the Panasonic, produce those low luminance blacks that are out of reach for LCD displays. The difference is seemingly miniscule to the point of unimportant, but cd/m2 is a logarithmic scale, and each minor change in black level has a significant impact on perceptible light levels. More on how we test black level.

Peak Brightness

This chart is a good demonstration of the difference between LCD and plasma screens. The Sony at the top is an LCD television, and it shows brightest whites at a luminance two to three times brighter than the two plasma screens in the middle. Our LG 50PZ950 uses plasma cells to make images, but it does not show the low luminance you tend to see, on either end of the spectrum. The brightest whites are well above average. For you, dear consumer, this means that you could watch this TV in most normal settings, not just in the darkest of cave-like environments. The LG 50PZ950 gets bright enough to compete with medium levels of light in the room. More on how we test peak brightness.

Contrast

We applaud the contrast ratio of the 50PZ950. We were a little worried about the it being heavily affected by a less than spectacular black level. Black level is the divisor in the contrast ratio equation, and when you divide something by less than one, each incremental diminishing has a large effect on the outcome, such that a difference of 0.01 cd/m2 is quite significant.

However, the 50PZ950 has a great peak brightness. This makes the range of possible lights and darks quite expansive, enough to show up the other plasma models in the comparison. With this strong contrast ratio, and a brightness that allows you to watch in low lighting, not just blacked out settings, we appreciate the middle ground this plasma has struck, without sacrificing quality. More on how we test contrast.

Tunnel Contrast

Plasma displays will change the brightness of the screen according to the images being shown. We test this by increasing the amount of screen displaying 100% black and recording the luminance at the center of the screen, which remains black throughout. You can see that the brightness at the center varied a little as these areas of black changed, but for a plasma screen, this is relatively insignificant. More on how we test tunnel contrast.

White Falloff

Plasma screens will brighten areas of pure white when they get smaller. Plasma cells get very hot when they show bright colors. Each cell uses quite a bit of electricity to activate, and the color white requires full activation of a cell. If the screen is just a blanket of white, each cell is at full activation, and the heat produced at peak brightness may be too much to safely display the image without overheating the unit. Thus, plasma screens will generally show dimmer whites when the screen shows a dove flying through clouds in a blizzard, and brighter whites when a crescent moon stands alone in a starless, night sky (secretly, we are all poets here).

The chart below shows how the 50PZ950 screen dims as white fills the screen from 5% to 100% area. More on how we test white falloff.

Uniformity

A true strength of plasma screens is how evenly images are displayed. LCD screens use lighting elements to shine through colored filters on a display to show images, sometimes LED lights, sometimes florescent tube lights. There is no way to arrange these lights such that they shine through evenly, and you will see blotchy patches from the lack of uniformity.

Plasma cells, on the other hand, are the size of individual pixels and active separately according to the input signal. They tend to be as uniform as the number of pixels on the display. On the 50PZ950, there are 1920 lighting cells across and 1080 going down in a matrix that shows a perfectly smooth picture with both all-black and all-white pictures. More on how we test white falloff.

Greyscale Gamma

The black and white performance of the 50PZ950 has been great to this point. Unfortunately, this greyscale chart looks awful. This graph indicates how well a television transitions from one value to another along a 255 value scale from black to white. Ideally, the line would be straight, sloping at 2.15, with no trembling.

What we see here is regrettably different. The smoothness is not terrible, there are little bumps in the line which show that certain values are skipped, so the great range we talked about earlier isn't fully employed. Instead of being straight, this line appears to grow in three waves. Often, we see an exaggerated version of this pattern when a contrast enhancement feature is turned on (and then we have to retest again, blast!), but all such functions were off. This shows us that the 50PZ950 is managing images in clusters: darks, middle grays, and whites. Each of these clusters has its own range of luminance.

We put up a greyscale gradient on the screen of the 50PZ950 and saw these deficiencies in action. The three clusters of luminance were readily evident. There was a hard grey line down the center of the gradient where the middle wave peaks in the graph. We noticed a hard black line and a hard white line in the dark and bright parts respectively, where the apex of these waves in the graph occur. Values in between these lines advanced in brightness in irregular blocks that were often too dim or too bright for their position along the gradient.

We are looking at a wash of grays, with only three areas that will stand out: Black, grey, and white, but not much in between. Detail and multitudes of values in the greys are needed to create a 3D image on a 2D plane. Without these qualities, you will see banding, loss of detail, and a flat picture. More on how we test greyscale gamma.