A small (6") portable TV with TFT display is presumed to use the usual
cold-cathode backlight. Does frequency of starting affect the life of
the tube - i.e. is it better to leave the set running for extended
periods, or keep switching it on and aff as required?

I have heard it suggested that these small tubes have a limited
lifespan and that replacements can be difficult or even impossible to
find or fit. Comments please?

TIA

--
ajb

In most of the very small LCD (TFT) screens up to about 8 inches, the
backlight is an electroluminance type wafer that gives off the light. Most
of the ones made with the electroluminance backlight, it is manufactured as
an integral part of the panel, and is not replaceable. In some of the
panels, it is a small type of fluorescent tube. In most of the very small
displays, and even in many of the larger ones, the backlight is not
replaceable. In many of the screens, the placement of the backlight is also
critical for the shading of the screen.

In both cases, it is a combination of the frequency of the powering on, and
the amount of hours used. Normally gas discharge tubes, such as fluorescent
tubes will have a reduced life span with power cycling. The start-up current
is hard on the tube. The electroluminance wafer is less susceptible to
increased wear from power cycling.

The average life span of the back plane lamp for LCD monitors is about
20,000 to 30,000 hours, with about a 50% average duty cycle for power on and
off cycling. This rating is for the 50% illumination point. The lamp may
last a bit longer or shorter than this average rating. If the lamp is rated
at 20,000 hours, it should have about 50% illumination or brightness after
this amount of hours. Some monitor manufactures rate their back plane lamps
to about 30,000 hours or more. This is because they are looking at more than
a 50% drop off in illumination to rate the lamp to be weak.

For most fluorescent tubes, during the first 100 to 500 hours, the
illumination may infact increase slightly, and then sort of taper off on its
way down. The wear curve is very gradual. For a 20,000 hour rated lamp,
after about 30,000 hours, the curve rate of drop-off would normally become
very steep, and the lamp will quickly fade out over a shorter time span.

If you use an LCD monitor for about 12 hours per day, and turn it off after,
this is a 50% duty cycle. You should be able to get about 1600 days or
periods of usage from the screen, to reach the 50% illumination point. This
would be about 4.4 years. So, you can say that you should get a bit more
than 4 years out of the screen. If the screen is on for 24/7, then this
would give about 830 periods or days of use. This would be 2.28 years of
use.

Since you may only use a computer monitor for about 3 to 5 hours on some
days, on others you may not use it at all, and then there may be days that
it would be used for maybe about 14 hours. In the end, the average projected
life should be about 4 to 5 years for the average person.

In 5 years from now, these monitors will probably be about 1/3 of the price
that they are now. And, the new ones will be far improved.

--

Greetings,

Jerry Greenberg GLG Technologies GLG
=========================================
WebPage http://www.zoom-one.com
Electronics http://www.zoom-one.com/electron.htm
=========================================


"ajb" wrote in message
...
A small (6") portable TV with TFT display is presumed to use the usual
cold-cathode backlight. Does frequency of starting affect the life of
the tube - i.e. is it better to leave the set running for extended
periods, or keep switching it on and aff as required?

I have heard it suggested that these small tubes have a limited
lifespan and that replacements can be difficult or even impossible to
find or fit. Comments please?

TIA

--
ajb