Folks here will try to pick apart the optical comparitor approach for various reasons. But if you use a bulb with CIE xy coordinates reasonably close to D65 (like the GE mentioned in my previous links), with a neutral white card that's a good match to the X-Rite/Munsell photo white cards, it should provide a pretty good reference for your TV's color temperature.
Is it as good as using a measuring instrument? Probably not. But it'll likely get you closer to the ballpark than any other low-cost method.
If you don't care what color the displays are though, and just want them to match, then you may not want to bother with this.