Edit, 8 p.m., Aug. 28: The trivia contest is now closed, and no further entries will be accepted. We’ll be back tomorrow to let you know the answer and choose a winner, who will be notified by email. Thanks to those who submitted their guesses!

Another $50 Amazon gift card is up for grabs today in the latest installation of our energy efficiency trivia contest! It’s the third in a series of questions we’re posting this summer and fall.

The full official rules are here, but we’ll summarize the basics for you:

•Each question will be posted here on our Stories blog at 8 a.m. on contest day. (We’ll promote them on social media beforehand — particularly on Twitter and Facebook — so be sure you’re following us.)

• You’ll have until 8 p.m. that same day to post your answer in the Comments section of the blog post. Answers posted on any other social media platform, or posted after 8 p.m. on contest day, will not be eligible to win.

•One correct response will be chosen at random, and the winner will receive a $50 Amazon gift card. Make sure to leave a valid email address as part of your comment, so we can reach you if you win — if we can’t reach you, we’ll have to choose another winner.

Also, we reserve the right to hide or delete comments not related to the contest. If you need help with a customer service issue, the best way to handle it is to call us at 1-800-DIAL-PPL (that’s 800-342-5775.)

Now that that’s out of the way, here’s this month’s energy efficiency trivia question. Remember, answers go in the comments:

According to ENERGY STAR, if every American home replaced just one light bulb with an ENERGY STAR-certified replacement, how much would America save on energy bills? (To clarify the question: We’re looking for the amount the entire country would save in annual energy costs if every home swapped in an ENERGY STAR bulb — not just the savings one home would get from swapping in one bulb.)