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Difference Side-lit LED versus Direct LED: pay attention when buying

Discussion in 'LCD & LED LCD TVs' started by LiquidB, May 18, 2009.

  1. LiquidB

    LiquidB Member

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    For sake of clarity:

    We are facing two different LED technologies today:

    1. Direct LED

    Here the backlight consists of hundreds of small LED's (usually white) which are divided into segments. The segments are referred to as a number of rows and columns.
    The LEDs are positioned directly behind the screen, over the entire surface of the screen. Doing so, you can locally switch ON, OFF or dim a segment where it is needed.
    This dimming, if done well by the TV manufacturer, enables the fabulous black levels in dark scenes or areas.
    The more segments, the more precise the dimming can be done and the less light leakage you will observe.


    2. Side-Lit LED

    Here the backlight consists also out of LED's, but in this case they are positioned not behind the screen, but on the sides of the screen.
    This has 2 big drawbacks:
    - You can not locally dim a segment where it is needed
    - If you look well, you will see that there is some light leakage at the sides of the display where the LED's are located.

    The second point may be improved by suppliers and may depend on sample/size.
    However, the first point is a definite drawback of the technology and puts the TV in performance comparable to it's CCFL brother. The whole problem is that the backlight is dimmed all over the screen in the same ratio.
    The blacks will look either washed-out because of light-leakage OR the light output in dark scenes will be dramatically low, due to dimming algorithms.
    Theoretically, you could also dim in rows or columns, but never in segments.
    This would not bring back the performance of direct LED backlight sets.

    So what is the advantage then? Well: the side-lit LED panels can be made very very thin and they consume less power than a CCFL TV. That's it.


    Be aware of this when buying a TV: a LED tv does not mean you ar buying a top PQ tv!
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  2. ash08

    ash08 Member

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    There was a thread last week that touched on this. I have a Samsung F96, the first LED backlight TV in the UK, complete with local dimming. I assumed that the technology would progress along the LED 'backlight' (eventually Multi RGB LED's I thought) path but it seems that the edge LED's have become popular in their own right. Like you say, this is mainly due to energy usage and the ability to use thinner panels.

    Theres quite a bit of confusion and its good to see a basic explanation. It seems as though Samsung have come under fire for a misleading marketing campaign for their new 'LED TV's' from some quarters...
  3. Mr-Bananas

    Mr-Bananas Member

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    LED back lighting with local dimming is surely the only way to go for LCD's

    This tech is capable of delivery phenomenal picture quality and helps to eliminate most of the LCD problems like uneven backlight and light leakage.

    I am a bit worried though, that so few models are out there.

    Apart from one or two models from Samsung and Sony, nobody else seems to be making them.
  4. AndyCob

    AndyCob Active Member

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    Think I posted on that other thread as well. Is the Samsung the first LED backlight TV in the UK? The Sony X4500 series uses an RGB matrix LED backlight with localised diming and they have been out for what 6 months+ (or is over a year) in the UK. Sony made a Qualia branded set with this feature 3-5 years ago, if I remember rightly, of course it was over £30,000 and not excatly widely publicised but it did exist to buy.

    I think LED has just become the latest 'must have' lable to entice the uninformed customer, the difference in simply replaceing the conventional light source with white LEDs versus local diming/RGB etc is lost on the average punter, just like HD ready caused so much confusion with things now changing to Full HD as a lable.
  5. Chris Muriel

    Chris Muriel Active Member

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    Above posters are correct in that edge lit LED backlighting is somewhat of a marketing gimmick; where it really helps the manufacturers in my opinion is that it allows the TV to be very thin (less than an inch) which scores high up the aesthetics scale.
    Joe Public will quite often be seduced by this and his wife even more so; hence they are scoring well on the WAF side of things (Wife Acceptance Factor).
    Behind the scenes at the IC manufacturers new LED controllers for true fully controllable, locally dimmable LED backlighting are being developed and I would expect these to become mainstream on new models within a couple of years.

    Chris Muriel, Manchester
  6. ash08

    ash08 Member

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    The F96 was the first LCD LED TV in the UK I think, came out in Nov 07. I picked mine up in June 08.
    I did read about the discontinued Sony's, I didn't know the price :)eek:) but it did state they were for the 'High End' market.
    Apparently LCD LED has been available elsewhere (Australia, USA) for a number of years in some form...
  7. KUBBY

    KUBBY Active Member

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    The OP has hit the nail on the head.

    This information should be available for everyone considering buying an LCD.

    I know that there is some way of preserving this,can a Mod consider this please.

    KH
  8. manowar68

    manowar68 Active Member

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    I bought a samsung led tv yesterday 7000 series and i have had a good look at all the sides and i have no light leakage what so ever.
  9. 5to1

    5to1 Member

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    I'm a little unsure how placing the LED's at the edge of the screen negates the other potential advantages LED backlighting can have over CCFL.

    For example it could still provide improved colour gamut. It could still provide more consistant colour over lifetime. It could still provide improved backliht lifetime. The reduced thermal output and hotspots could improve the life of other components. It could still provide improved resiliance both for transport and backlight failure (losing one of many backlights is not a disaster, whereas losing one of one or two is). It could provide more consistant backlighting of the panel.

    Even with respect to dynamic backlight adjustment, edge-lit LED systems could potentially be controlled in smaller and more consistant increments then their CCFL counterparts.

    I'm not saying the current generation necessarily have all these advantages. But the potential is there.
    Last edited: May 18, 2009
  10. ziffius

    ziffius Active Member

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    CCFL LCD TVs don't just have one or two backlights. The 46A530 for example has 22! Here's an inverter for one http://cgi.ebay.com/Samsung-Back-Li...emQQptZLH_DefaultDomain_0?hash=item3c9e500923

    LED backlighting is nothing more than a stop gap until the real deal OLED gets upto speed.
  11. 5to1

    5to1 Member

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    I was just giving the worst case example to illustrate the point. The number of CCFL backlight units will depend on the size and budget of the display.

    Even taking the highlighted case of the 46A530, you're more likely to notice the failure of one of those 22 CCFL backlights, then 1 of the LED's in the Samsung LED displays.

    WRT to LED backlighting being a stop gap, it's already been around for a few years in display devices. With OLED's progress still not clear it looks like it will be around for a while yet. And even when OLED does show up, its likely to be at the top end of the price bracket for some time. Therefore I would hardly describe it as a stop gap.
    Last edited: May 18, 2009
  12. LiquidB

    LiquidB Member

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    Some extra answers:

    1. On reliability, the Side-LED TV's are performing worse: you need to make as much light as on a direct LED, but with fewer LED's. This means you need to use high-power LED's and drive them to the maximum. This means your average light output willl decrease over time.
    This could also explain why Samsung only outputs 65% of the light output in home mode versus shop mode: in shop mode, they let them 'burn up'.

    2. On the availablility of direct LED's I can say the following: look at Philips 9803 and 9704. They are all direct LED.


    3. The light-leakage of a side-LED can be best judged on a black pattern.
  13. 5to1

    5to1 Member

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    1) Given that edge-lit LED is the more mature application and "direct LED" is relatively new I'm unsure where you're getting your figures from.

    To address some of your concerns, like most solid state devices its thermal properties of the application which are the key determining factors of lifetime.

    In two isolated LED's of the same type it may be correct to state the one outputting the most light is likely to fail first. Since light output and thermal output are related. However, in real world applications this is often mitigated by using components with higher tolerances or mechanisms to disipate heat.

    To give you some examples the fact that less LED's (although this depends on specific applications and doesn't always hold true) are used in an edge-lit display may allow the manufacturer to use superior components. Moreover, the fact that less LED's are used and they are spread over a smaller area, could allow the manufacturer to use superior mechanisms to disipate heat. Having several heatsinks/fans spread accross the screen would be more costly then having 2-4 along the edge of the screen.

    Ofcourse having the LED's spread accross the screen may help disipate heat, and in higher end screens they may still use superior components. But the point is your statement that edge-lit displays will have poorer reliability then "direct LED" ones because of the nature of how edge-lit displays work is clearly incorrect. As I've highlighted, some of the points which you make can actually be positive when it comes to reliability.

    WRT shop mode, I think you'll find having the backlight set to 100% in this mode is not something restricted to edge-lit displays. Therefore its incorrect to apply anything you infer from this practice solely to edge-lit displays. Of the many displays I've had, I've never run any of them near the backlight setting the manufacture/retailer has used on the shop floor.

    People need to remember edge-lit LED backlighting is quite a mature technology. I've had several over the past 3 years.

    2) I tihnk you can still get some of the Samsungs if you look hard enough. I'm not sure how well the Philips have reviewed, I know the Samsungs suffered from artifact issues.

    3) I've tested mine in a dark room on a black screen and don't see any backlight bleed. On other edge-lit displays I have seen varying degree's of backlight bleed. But IMO the extent of the issue hasn't been any different to most other backlight technologies.

    You should remember that while the location of the backlight units on edge-lit displays could result in greater likelyhood of light leakage from the edges of the panel. The directed nature of light produced by LED's makes it easier in some respects to prevent light leakage.

    The extent of light leakage is determined more by the individual implimentation, then the backlight application.

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