Hey Toot, the short answer is no, it won't pay for a long long time. I'm making some assumptions here, because I don't know what your electric rates are, but if they are similar to average rates across the US, at 15 cents per kilowatthour (kwh), it will take years to pay back the $40, maybe 40 years or so. We live in a home that is powered by the wind and sun, so in the end, we probably pay more for our electricity than if we bought it off the grid. Really, grid power in most places in the US is pretty cheap, most people just use so much that their bill climbs into the hundreds of dollars per month. One LED bulb like that that saves you a couple watts might save you 5 cents a month if you ran it several hours a day, you can do the math after that. What I'm getting at is even with our limited power production, I do not use LED's in most of my fixtures. I have a few low voltage strips under the cabinets, and I use LED Christmas strings for decoration and limited outdoor lighting, but the rest of the house is CFL.
If you could find an LED bulb that used 4 watts instead of 16, it would save you 12 watts. If you ran it 3 hours a night, that would add up to 1 kwh of savings each month, or about 15 cents. After 5 years, or 60 months, your total savings would be $9.00 USD. You could probably do better putting your $40 in a long term investment. Not that the dollar cost is the only thing to consider, the reason we make our own electricity is environmental in our case. If you have a fixture that is on all night, maybe an LED makes sense there, even if it doesn't entirely pay for itself in electric cost, you're still reducing your use, that is worth something. Good luck, and take care, Rudydoo