Hi there Stewrt,
Yes, in the end I found out that essentially it is a single light that indicates the status/level of the treble and bass. There are 8 lights in total, and as you increase/decrease with the remote, the lights with pulse dimly then light up in full, before moving onto the next, until it reaches the 8th one. You know when its at the max when the final led becomes slightly brighter than it was before, reaching its full brightness means its hit the top.
It's not the most intuitive method by far, and should have been detailed more in the manual, but it works. What is strange, is that to get that loudness and treble and bass, even at their max settings, you have to turn the SoundBar on, then turn Audio Volume on the remote Off, then press On again, for a marked difference in sound.
Other than that, Im happy with my purchase still after all this time, its an improvement over the Samsung UE55f8000 built in speakers for sure, but mainly due to the low cost rather than performance. In the last week funnily enough, Ive ordered two Sonos Play:1s and a bridge to begin the process of paying a home theatre Sonos setup (just need the play bar and sub woofer to complete) and the stereo set up of a pair of Play:1s already sounds better/meatier than the single play bar, Im looking forward to the full set up to see how much better it becomes.
I intend to keep the HTL5120 but place it in a different room/office area as its definitely an improvement over normal tvs, just maybe not the wow factor you were hoping for with a single piece of kit. The Sonos set up is expensive, and Im sure more learned audiophiles would say its better to buy a proper audio set up for half the price, but Im already in love with the wireless nature (reason I bought the HTL5120 in the first place was to remove clutter) and the ability to push music into other rooms.
Hope that helps, all the best,