Is your LED screen backlight needlessly at 100%?

Roderick Stewart Wrote in message:
On Sat, 25 Jun 2016 09:19:02 +0100, Ian Jackson
wrote:

I've just replaced 2 LED strips on a 50" LG less than 2 years old. It
seems that LG set backlight current at maximum by default and it's
becoming a known problem with LG's.

Just as an aside, can anyone briefly explain the concept of 'backlight'?
Why is it necessary, and how does it differ from 'brightness'?

Liquid crystal displays don't emit light. They are effectively
transparent filters that can only vary their densities, so that to be
visible they need either a reflective backing or a light behind them.
Those silvery-grey number displays on some electronic devices are
liquid crystals with a reflective backing, and need incident light
from the front to be visible.

TV and computer screens have an evenly distributed diffused light
source (either fluorescent or LED), which without the LCD screen in
front would simply display a white rectangle. The brightness of this
determines the maximum possible brightness of any part of the display
where the LCD is at its minimum density. What adjustments are possible
would depend on what controls are provided and how meaningfully
they're labelled, but I would suggest that what to aim for is to set
the video gain so that peak white corresponds to minimum LCD density
(ideally by checking for the the top levels of a staircase test signal
just beginning to crush), then set the backlight to make that part of
the picture whatever brightness you want. Then you should use only the
video controls to set black levels, because black is determined by the
maximum density of the liquid crystal and backlight won't have any
effect on this without having a much greater effect on the white level
you've just set.

Rod.


That's an excellent explanation. Thank you.
We have come a long way since the first generation of LCD screens,
I remember the first one I tried to set up, a 14 inch TV. the
controls had the traditional names, contrast and brightness,
but they interacted to such a degree the names seemed arbitrary.
Even a slight change in viewing angle messed it all up.

--

%Profound_observation%


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On 25/06/2016 09:19, Ian Jackson wrote:


Just as an aside, can anyone briefly explain the concept of 'backlight'?

They're so nobody runs into you at the back.

Bill

On Sat, 25 Jun 2016 13:23:56 +0100 (GMT+01:00), "Graham."
wrote:

I can understand this for the fluorescent kind of back light, but I thought
LED ones were immune.
Brian


You would think so wouldn't you?
Perhaps the less well designed sets over-run the LEDs when set
near maximum.

The first batch of GU10 LED spotlights I bought certainly weren't
immune. I must have replaced about thirty halogen types in three
family kitchens and bathrooms, but ended up replacing most of the new
LEDs in the first few months. Thankfully quality control for these
things seems a bit better now.

Rod.