Another day, another fight over... lightbulbs. Yes, lightbulbs.

Back in 2007, Democrats in Congress passed a bill to increase the energy efficiency of the most common types of lightbulbs in the United States. This was often referred to as a "ban" on incandescent bulbs since the law would effectively phase out the manufacture and import of those cheaper, old-fashioned incandescents by Jan. 1, 2014.

In their place, manufacturers have been offering more efficient (but also more expensive) compact fluorescent, LED, and even incandescent bulbs. But the newer bulbs aren't always popular, and conservatives have long criticized the rule.

Now there's a new twist. Congress is getting ready to vote on a $1.012 trillion spending bill for 2014 that would bar all funding for enforcement of the new lightbulb standards. That rider had been pushed by Republicans for years. Now they may finally get it passed.

The catch? It probably won't make much practical difference to U.S. manufacturers, who have largely switched over to making newer, more efficient bulbs. But it could create a loophole for anyone who wants to import the old bulbs. Here's a rundown:

What are the lightbulb standards, anyway?

Back in 2007, Congress passed a law that would set higher efficiency standards for the most common lightbulbs. The first set of standards would require the bulbs to use at least 25 percent less energy and were scheduled to take effect between 2012 and 2014, like so:

That means, starting in 2012, all 100-watt bulbs that were manufactured in or imported into the United States have to meet these standards. Those rules extended to the more common 60- and 40-watt bulbs on Jan. 1, 2014.

Now, incandescent bulbs aren't "banned" under this standard, as is often suggested. Manufacturers can still produce incandescents, so long as they meet these energy standards. Companies like Philips have been doing just that, putting out incandescent bulbs that are filled with halogen gas, so that the filament burns more efficiently.

But it's true that the traditional, cheaper incandescents that cost 50 cents a bulb are getting phased out, since they can't meet the standard. As of Jan. 1, 2014, it is illegal to manufacture or import these bulbs. Stores can sell off their remaining stockpile. But, eventually, those old bulbs will be gone. Home Depot says it only has a supply that will last six months. (There have even been reports of bulb hoarding.)

By the way, this is just the first round of standards. By 2020, lightbulbs will have to be 60 percent more efficient than the old models.

So what kind of bulbs will be available?

Manufacturers have been offering three broad types of bulbs to replace the old incandescents:

Compact fluorescent lights: These are the swirly bulbs. They typically cost more than incandescents but use around 75 percent less energy and last up to 10 years. (Many 23- to 27-watt CFL bulbs, for instance, put out as much light as a 100-watt incandescent.) Depending on the bulb, it can take a few months to a year for homeowners to recoup the higher upfront costs through lower energy savings.



LED bulb. (Philips)

LEDs: These bulbs tend to last the longest and use up to 80 percent less energy than traditional bulbs. But they're pricey. For instance, an LED that's the equivalent of a 60-watt bulb can cost between $5 and $22 (vs. $1 or less for the old incandescent). But, at least in theory, that light should last up to 22 times longer and use less than one-sixth the electricity.

Halogen incandescent bulbs: Many people prefer the warm yellow light that comes from incandescents, and halogens are the most similar to old-fashioned bulbs. These tend to be cheaper than CFLs and LEDs, but they're not quite as efficient and don't last as long. (They use about 25 percent less energy than the old incandescents — and they also won't be able to meet the stricter 2020 standards unless they continue to get more efficient.)

The Natural Resources Defense Council, a supporter of the law, offers a guide (pdf) to the different types of bulbs currently on offer.

Why did these standards come into place?

The official rationale is that the rules help save energy. Back in 2007, the Energy Department estimated that lighting for homes and businesses consumed about 300 billion kilowatt-hours of electricity each year, equivalent to about 100 power plants. And much of that energy was wasted. The traditional incandescent bulb converted just 10 percent of the energy it used into light. The rest was lost as heat.

But that wasn't all. The biggest lightbulb manufacturers — General Electric, Philips, Sylvania — also lobbied hard for the rules. As Andrew Rice reported for The New York Times Magazine in 2011, these companies had long lamented the fact that the cheap old incandescent bulbs weren't very profitable to make. And Philips, in particular, had been investing in efficient new LEDs and fluorescents in response to tightening standards in California and abroad. Yet consumers in the rest of the United States didn't seem very interested — unless, that is, there were regulations to force the transition.

So environmentalists and lightbulb manufacturers worked together on the new standards. Green groups liked the energy savings. And companies like Philips liked the fact that they were well-positioned to capitalize on the newly created market for efficient bulbs.

What's the main argument for the law?

Proponents argue that the rules save energy and money — and that the newer bulbs are increasingly innovative and no longer give off the harsh light that used to be common with CFLs.

As noted above, the bulbs cost more upfront. The upside is that they're supposed to cut down on electricity bills over the longer term. The Department of Energy estimates that using a traditional incandescent bulb adds about $4.80 per year to the average electricity bill. But a CFL bulb adds just $1.20 per year and an LED bulb $1 per year. Add it up, and a typical household could save about $50 per year by replacing 15 old incandescent bulbs.

In theory, that could add up to major electricity savings. If LED bulbs became widespread, the Energy Department estimates, then by 2027 the country would save as much energy as that put out by 44 large power plants. That's an optimistic scenario, though.

Meanwhile, Time's Michael Grunwald has argued that the standards have "inspired a flurry of made-in-America innovation," as manufacturers tinker with new models and prices plummet. For instance: "Ohio-based Advanced Lighting Technologies is releasing the Vybrant 2x, a 21st century incandescent powered by nanotechnology. It lasts twice as long as an old-fashioned Edison bulb and uses 50% less energy."

What's the main argument against the law?

It's a restriction on consumer choice. By the numbers, at least, Americans still prefer the old-fashioned incandescents. In 2013, those old-fashioned bulbs were, by far, the most popular in the country:

Over at Reason, Shawn Regan lists a number of other common complaints with the newer bulbs: "They are often slow to respond, sensitive to high temperatures, and can cast a harsh and unattractive tone. CFLs also contain a small amount of mercury, which requires extensive and careful cleanup when a bulb breaks."

That's why many Republicans still support repealing the regulations. "If the new energy-efficient light bulbs save money, and if they’re better for the environment, we should trust our constituents to make the choice on their own move toward these bulbs,” said Rep. Michael Burgess (R-Texas) last year. “Let the market decide.”

So what did Congress just do?

Tucked inside the $1.012 trillion spending bill that Congress is considering, there's a provision that would bar funding for enforcement of the new lightbulb standards. (It's the same bill that Burgess was pushing last summer and which he added to a 2011 budget bil.) That means the Energy Department can't spend any money to prohibit the manufacture or import of old bulbs.

Will this enforcement provision make any difference?

In some ways, no. All of the big manufacturers — General Electric, Philips, Sylvania — have been working for years to comply with the new standards, churning out new CFLs and halogens and LEDs. They're not expected to change course now.

But some stores could, in theory, try to sell the older incandescents if they can get their hands on them. Opponents of the enforcement provision have worried that foreign companies will do exactly that. "Given that American manufacturers have committed to following the law regardless of whether or not it is enforced," said Rep. Marcy Kaptur (D-Ohio) last year, "the only benefit of this ill-informed rider is to allow foreign manufacturers —who may not feel a similar obligation—to import noncompliant light bulbs that will not only harm the investments made by U.S. companies, but place at risk the U.S. manufacturing jobs associated with making compliant bulbs."

Whether that happens or not remains to be seen. It's still illegal to make or import old lightbulbs. The rider just makes it a little easier to get away with it in practice.