I have a Phillips LCD which is getting close to being 10 years old. Still ticking along just fine. 

Like any electronics, that is highly variable. It may outlast you or it could quit as soon as you plug it in. I've seen high quality electronics die suddenly and low cost stuff that is still going strong after years of constant use.  There are way too many factors involved, such as heat, vibration, humidity, low or high voltage, surges,component quality,physical abuse, etc. to pin down a "life expectancy" 

Cost or time in service often has little bearing on the lifespan.

You might as well be asking "How high is up"? or "How long is a peice of rope"?

There has been times where it's been on for several weeks at the time.

Thanks for the link RedneckDude. However how do I tell what backlight source my TV uses?

Didn't come with one. Company says everything is posted online. I went to the website and read through the manual. No mention of what kind of backlight the TV employs.

Kona...post the brand and model number etc....perhaps someone can have more luck hunting down the info.

Many televisions use componentry from external sources...

Why do you want it on all day?

Seriously, there are only so many times you can watch Avatar.

It's tube-lit.

Generally speaking, if it's a couple of inches thick it's probably tube-lit. If it's extremely thin, it's probably LED-lit. LED-lit sets have only become common in the past year or so and generally cost more, and you can rest assured that stores make it a point to advertise LED-lit sets as "LED TV" to make it seem like it's not an LCD. But the difference mostly a matter of power and longevity. LED-lit sets actually have poorer color reproduction unless you spring for the high end ones with full-screen lighting that adjusts with the picture brightness.