It sounds like the 8' lamps may have gone mercury-starved.  Over time the mercury inside a tube may be absorbed.  It's still there but no longer evaporates during use to contribute to light output.  This occurs more often these days now that they no longer add as much surplus mercury for environmental/disposal reasons.

Another possibility is that the ballast is no longer providing full power to the lamps.  The only way to be sure is to replace the tubes and see what happens.  New lamps may start out dim but should reach full output within a few minutes.  If they remain dim, the ballast may be faulty.  If it's bad or you simply don't like having a PCB-containing ballast around, non-PCB replacements are available.  Eight-foot T12 fixtures are starting to go by the wayside, in favor of multiple four-foot T8 fixtures, but most big box stores will still have the parts.

You could really replace the kitchen light with any ceiling fixture.  It'd be easiest to go with something at least as large in diameter to avoid repainting, and keep in mind your current light output is about 2800 lumens or a little over the output of a 150W incandescent bulb.

PCB我不知道是啥，好像是多氯联苯，我们国家早期的镇流器都是灌的沥青的，和美国的差不多，都是铁盒子的那种，然后带引线出来的，这种镇流器现在已经全停产了，没有厂家生产了，都是欧洲的那种的了，而且漆包线也改成铝的了。

Patrick and Ash:

Thank you for taking the time to respond again and for all the good information you passed on to me. The property caretaker removed the cover of the fixture in the basement and the ballast looks to be the HPF green and yellow universals and isn't labeled "no pcbs" but there was no sign of any leakage. They decided that they will replace the lighting with LED fixtures anywayss.

Thanks again!

They decided that they will replace the lighting with LED fixtures anywayss.

Insist on not having LED, as other kinds of lighting are likely better.

The marketing LEDs get is impressive (they are the most profitable for the lighting industry), but they are not the one end-all solution as one would believe. Modern Fluorescents have better light quality (good contrast but it does not appear "intrusive"), light distribution across the area, lower glare, and (compared to "built in lamp" type of LED lights) easily replacable lamps when they burn out

In this case, the best option (and cheapest for the same results) is to keep the body of the Fluorescent light, and upgrade the ballast inside to a new electronic ballast. As a side benefit, the electronic is more energy efficient than the old one

There may be more than one type of Fluorescent lamp that can fit into the same length and sockets. Since you replace the ballast, you get to choose which type to go with from now on, and pick the ballast for it

Tell us :

 - what lamp type is specified on the ballast

 - what is written on the lamps

 - what sort of connector they have

 - what size of area it lights and how bright you need it

 - for how long the light is switched on at a time (estimated)

so we can see what your options are and suggest something

Regarding the 8-foot fixture, those green and yellow Universal ballasts tend to be pretty good, but since yours is high power factor and doesn't say "No PCBs" it's safe to assume it has a PCB-containing capacitor inside. I would just install a new pair of lamps and leave it alone, but if you'd be more comfortable getting rid of it, then that's what you should do.

Replacing the whole thing with LED is an option, but you can also just replace the ballast for not much money. This ballast would work if you wanted to use F96T12 lamps (which I assume is what you have), or for a little extra energy savings, you could use F96T8 lamps with this ballast. Both the T12 and T8 lamps should fit in your fixture with no changes needed other than the ballast. One thing to keep in mind, though, is that the electronic ballasts I linked to don't wire up the same way as the old magnetic ballast.