From Nookipedia, the Animal Crossing wiki
Spotlight items first appeared in Animal Crossing: Wild World as a replacement to the Lottery. Every so often, Tom Nook will place an item in his shop with a light shining on it. This is the spotlight item, and can only be bought from Tom when in the spotlight. In Animal Crossing: New Leaf, they appear in Timmy and Tommy's store when it has upgraded to T.I.Y.. They can also appear as items from Mom or Wishy the Star. They are worth +151 points to the HRA. Everyday there is a spotlight item, there will be a notice on the bulletin board.
The following spotlight items give additional luck when placed in your house.
The following spotlight items are deemed 'Lucky' and are worth +7,777 points to the HRA.