To compare 240Hz vs 120Hz refresh rates it is necessary to appreciate that there is a 240Hz refresh rate and 240Hz effect which is not actually a 240Hz refresh rate.

240Hz Refresh Rate

When a HDTV is advertised as having a 240Hz refresh rate it indicates that the refresh rate has been achieved by the software running on the video processor creating a suitable number of interpolated frames to add between the frames of the video source. Frame interpolation is based upon the knowledge that the smoother the track of an object across a screen the less likely the human eye will perceive it as being blurred. Each interpolated frame places moving objects at intermediate positions between their positions in trailing and leading frames thus smoothing the motion track and reducing or eliminating perceived blurring.

240Hz Effect

A HDTV advertised as having a 240Hz Effect has a combination of frame interpolation to achieve a 120Hz refresh rate and scanning backlight technology which also acts to reduce perceived motion blur. Calling it a 240Hz Effect acknowledges that backlight scanning improves blur reduction beyond what is achieved by the 120Hz refresh rate. Backlight scanning is based on the knowledge that the at interruption of constant light reduces the likelihood that the human eye will perceive motion blur. Scanning backlight technology has been used in conjunction with frame interpolation by Sony, LG, Toshiba, Philips and Vizio. The image below shows this combination as used in Sony’s MotionFlowPRO brand of anti-blur technology.

Anti-blur Technologies 120Hz, 240Hz and 240Hz Effect Compared

A conventional LCD HDTV displays video at 60Hz and is susceptible to having viewers perceive motion blur when there are fast moving on-objects such as during sports broadcasts or action films.

If you watch sports and actions films a 120Hz refresh rate display will provide an improvement in noticeable blurring. As an added bonus, the frame interpolation also reduces judder which may also be noticeable during movies where the 24 frames per second film has been boosted in frame rate through a process known as pulldown.

Both 240Hz and 240Hz Effect do provide a further improvement in anti-bluring capability beyond a 120Hz refresh rate for the differing reasons explained. The difference between the two technologies and to 120Hz is difficult to determine as the performance of the human eyes looking at the screen start to have an influence on the result. Put simply, both are better than 120Hz but, the degree and whether it is worth the cost is down to the individual.