The Sony X850F vs X900F differences are mainly found in the backlight type (which has an effect on the screen uniformity), picture processor (determines the quality of upscaling based on whether it can perform dual database or only a single database processing as well as whether Dolby Vision is supported or not), dynamic range (reveals how well HDR content can be reproduced), motion technology (affects the luminance depending on whether the backlight blinking is done globally (i.e. entire backlight) or locally (only select zones) for the purpose of improving the motion clarity), design (different stand).
1. Different backlight type (Edge vs Direct LED)
The X850F has an Edge-lit LED backlight whereas the X900F features a Direct LED (full-array backlight in particular). There is a difference in where the LEDs are placed: on the X850F they are alongside the edge of the screen which necessitates the use of a light guide plate in order for the light to be distributed across the screen. In case of the X900F, the LEDs are spaced evenly across the back of the panel which leads to a less variation in the light output in different areas of the screen, hence the more even screen uniformity on the X900F vs X850F. That being said, in order for any imperfections in the screen uniformity to be observed requires most (if not all) of the frame to show unifrorm color (at the same luminosity level) which rarely happens during regular content viewing. One exception being the letterbox bars in widescreen movies.
2. Different 4K HDR Picture Processor (X1 vs X1 Extreme)
The difference in the X850F and X900F’s processing power affects the 4K X-Reality PRO technology that both of them have because it determines whether this clarity enhancement technology is augmented with dual database processing or not. The X850F’s X1 chipset is able to process only a single upscaling database. The X900F’s X1 Extreme chipset, on the other hand, is powerful enough to support Dual database processing. In addition to the aforementioned upscaling database, the X900F utilizes a second database for compressed image noise reduction. The X900F therefore has the upper hand, especially when it comes to upscaling poorly compressed content. However, the fact that the X850F’s X1 processor and the X900F’s X1 Extreme chipset share a number of features, such as Super Bit Mapping, Dynamic Contrast Enhancer, and Object-based HDR remaster, cannot be ignored. When watching Blu-ray discs or Full HD programming, for example, the difference between the X850F and X900F is mostly diminished. Another difference between the X850F and X900F is that only the X900F is able to support Dolby Vision (via a future firmware update) thanks to the X1 Extreme processor. The X850F cannot be updated to support Dolby Vision. Furthermore, the X850F’s X1 processor doesn’t support Precision color mapping which can be found on the X900F, also owing to the X1 Extreme chipset.
3. Difference in the dynamic range capabilities
The X850F has an edge-lit LED backlight that can only perform frame dimming. Considering that both highlights and shadows (as well as mid tones) are darkened when the X850F’s edge-lit backlight is dimmed, there is no change in the dynamic range. The X900F, on the other hand, has a Full-array local dimming and boosting backlight. This means that the backlight zones on the X900F can either be dimmed (thus enhancing the black level), boosted (rendering highlights brighter), or both dimmed and boosted within the same frame (thus increasing the dynamic range between shadows and highlights which is needed in order for HDR content to be reproduced more faithfully). The X-tended Dynamic Range PRO 6x technology the X900F is equipped with delivers a contrast range six times that of a conventional edge-lit LED TV without local dimming such as the X850F. The difference between the X850F and X900F with HDR10 content is most apparent in the specular highlights which are significantly brighter on the X900F in comparison to the X850F.
4. Different Motion technology (Motionflow XR vs X-Motion Clarity)
The X850F utilizes the Motionflow XR technology whereas the X900F uses the X-Motion Clarity. The difference between them is that the X900F uses its local dimming and boosting zones in order to restrict the backlight blinking only to the zones where the motion is concentrated instead of having an entire black frame inserted between the original frames which would lead to a sizable reduction in brightness as well as visible flickering (depending on your susceptibility). The X900F’s approach prevents the moving object from appearing blurred across different frames (by the means of providing a break in the continuous light output so that the retinal persistence can be cleared) without affecting the overall image brightness. Additionally, some of the backlight zones can be boosted if required. The X850F doesn’t have a full-array local dimming and boosting backlight so it omits the X-Motion Clarity technology. That being said, both the X850F and X900F resort to using motion compensated frame interpolation in order to increase the smoothness of motion. You can adjust the level of generated intermediate frames to your liking. Furthermore, the X850F and X900F both have a native refresh rate of 120Hz.
5. Different table top stand
Although the design is mostly identical on the X850F and X900F, it should be said that the table top stand is different. The two feet of the X850F’s stand are in the form of an inverted V whereas on the X900F they are L-shaped. The color is also different: the X850F has a silver stand while in case of the X900F it is dark silver. You can route cables through the legs of the stand that is supplied with either the X850F or the X900F in order to have a cable-free front. Another difference between the X850F and X900F is due to the X900F’s full-array backlight which makes it approximately 0.7 inches thicker than the X850F.