My Hampton Bay ceiling fan has upper and lower lighting. The upper light works fine but the lower light just has a warm glow like it in not getting full power.

Did you just install a new fan? If so, 1st check the wattage for that lower light, some two lite fixtures have a night lite which are designed that way just check the wattage and if that's not the issue than either there's a loose neutral under the wire nut either under the ceiling canopy or at the lower connection which should be a push in connection,make sure the wire colors are correct,white to white and blk. To blk. Or blk. To blue... Usually when people connect all the proper wires under a wire nut the small fixture wire is the last to get connected together and isn't as tight under the wire nut as they think making an intermittent connection.. Check it

Has it always been like this?