Lamp replacement - timing thereof

Mr Incredible · 16-01-2005, 12:37 PM

My Sony 50" LCD RP-TV is over six years old with the original bulb still going strong.

Over that period I cannot tell wether the picture contrast/brightness is as good as it was when it was new. Should bulbs be replaced after their nominal life expectancy is exceeded to ensure optimum quality? Or is the case that PJ bulbs do no deteriorate in "quality" over time: either they work or they don't?

Curious.

**LV426** · 16-01-2005, 1:12 PM

I just replaced the lamp in my Sony projector after 1850 hours (rated at 2000). It still works and I'll keep it as an emergency spare. However, the brightness had clearly deteriorated hugely, as evidenced by the vastly increased brightness of the new lamp.

So.....yes, I'd say. Did your set come with a spare? If not, then I wish you well in sourcing one.

Mr Incredible · 16-01-2005, 1:36 PM

Interesting. If a lamp does lose its brightness over time, is it not the case that with LCD panels you could just increase the "brightness/contrast" level on the TV? After all, its not changing the output of the bulb, rather the opacity of the RGB LCD panels.

Then again if brightness is related to temperature, and colour related to temperature, I'd be more concerned about colours being off what they should be.

My TV did not come with a spare lamp. At £200 for a replacement I was willing to order as and when required. Are you suggesting I will have a problem sourcing a XL-100e lamp? If so I'd better get my plastic flexible friend out of my wallet b4 its too late!!

Nick_UK · 16-01-2005, 1:41 PM

If the lamp in your TV is the same type as that used in my projector (high pressure mercury vapour), and I suspect that it is, it might not be a good idea to wait for the lamp to fail. It's not unusual for lamps to explode when they fail, and it's a messy procedure to clean it up. You even run the risk of damage to the optics. It's best to change the lamp at the intervals suggested by the manufacturer.

**LV426** · 16-01-2005, 2:00 PM

LCD panels are passive (as I'm sure you realise) - meaning that they simply filter the light coming off the lamp to a greater or lesser degree.

LCD panels are also limited in their contrast range. In order to get the most out of any LCD-based display, it is necessary (and I guess you probably have already done this, perhaps without realising it) to have the contrast and brightness values fairly critically set, so that:

peak white corresponds to fully transparent LCD pixels
true black corresponds to (as) fully (as they can be) opaque LCD pixels.

Hence, turning the brightness or contrast up, simply narrows the range between light and dark. You can't increase the brightness of a fully transaperent pixel.

As for sourcing a lamp - it's a good few years since these TVs were sold, so you may find them hard to come by.

Mr Incredible · 16-01-2005, 2:05 PM

AFAI can tell, the "bulb" is a cartridge affair, fully sealed. The manual says that if the bulb "goes" it will make an audible sound and is no indication that damage has occurred. It suggests replacing the bulb if the picture goes dark or the colours change. As far as I can see my piccy is as just good as it ever was. But then again how would I know?!!! Sometimes I can't even remember what I did last week never mind the comparative results of picture quality over 6 years!!

Mr Incredible · 16-01-2005, 4:17 PM

Quote:

Originally Posted by LV426

peak white corresponds to fully transparent LCD pixels
true black corresponds to (as) fully (as they can be) opaque LCD pixels.

Hence, turning the brightness or contrast up, simply narrows the range between light and dark. You can't increase the brightness of a fully transaperent pixel.

True. But the "brightness" setting on the TV is no where near its "max" suggesting that the LCD pixels are not fully transparent. The level at which it is set for day to day use gives me vibrant but not washed out colours. Additonallly I have a DVD (Monsters Inc I think) which I can run the "tests" to set the contrast / brightness at the correct level. Again these have plenty of latitude on their min/max settings suggesting the unit is operating reasonably well within its tolerance limits.

Cheers

**LV426** · 16-01-2005, 4:38 PM

Brightness is used to control black level. Contrast is used to control white level.

Turning either too high will result in loss of detail in bright areas (eg no differentiation between white cloud and very bright sky.

Mr Incredible · 16-01-2005, 4:51 PM

Ah, wasn't sure which was which, but I should have known considering that the DVD set up (the same for PC monitor set up) sets contrast first to make the darkest areas appear black, then adjusts brightness. In my case the contrast level @ +/- 80% of max is more than what it was originally for a "decent" picture, suggesting that the brightness has reduced somewhat. But as the Monsters Inc test patterns show that I can still obtain a superb picture perhaps I shouldn't worry too much!!

Thanks for taking the time to converse!