John_newJohn Drengenberg, consumer safety director at UL, answers burning questions about compact fluorescent light bulbs (CFLs) and light-emitting diode light bulbs (LEDs). (Photo: UL)

To submit a question to John, email with "Ask John" in the subject line.

Dear John: Can I put a new LED light bulb in an old lamp? What wattage should I choose?

Yes. As long as they have the same screw-in base, an LED light bulb would work fine in a lamp, wall sconce or ceiling fixture. Wattage refers to both brightness and electricity. The wattage comparison between incandescent bulbs and LEDs can be confusing. Consumers should carefully read the packaging to understand the wattage comparison between incandescents and LEDs. Most manufactures will put on the packaging what the incandescent equivalent for the LED is. As for what wattage to choose, that depends on your lamp. A label should be included somewhere on the fixture detailing the maximum number of watts safe to use. Don’t buy a bulb stronger than that.

The difference is this: When you replace your incandescent with an LED, you’re going to use 75 percent less electricity. Lighting is about 13 percent of your electric bill. And on top of that, LEDs (and CFLs) will last about 25 times longer than the old incandescent light bulbs. So even if you’re spending up to $10 for one light bulb, you’re really getting a good bargain.

Lastly, look for the UL mark on the LED bulb (or CFL bulb), which means representative samples have been tested and met the rigorous safety standards of UL. And make sure you turn off the lamp or fixture as you replace the light bulb.

Related: Ask the Expert: Home Inspections

Dear John: Should I be worried about radiation emitted by CFL and LED light bulbs?

No, there is no need to worry as there is very little radiation emitted from CFLs and LEDs. In fact, with light bulbs, especially the CFLs, the radiation from the lights is no different than what you’ve experienced for many years being under fluorescent lights in schools, stores and office buildings.

Dear John: Should I worry about the mercury in CFL bulbs? And what should I do if I break one?

There’s no mercury problem with a CFL bulb unless you break it. Mercury is not leaking out of the bulb — it’s inside the glass tube. The mercury is absolutely necessary. It interacts with the phosphor coating on the inside of the glass to make the bulb fluoresce. But if you break the bulb, yes, there is mercury inside. It’s about 5 milligrams, enough to cover the head of a pin.

If a CFL bulb breaks, it’s not a terrible catastrophe and you don’t have to don your hazmat suit. Let it sit for a little while to let the dust settle. Don’t sweep it with a broom and don’t vacuum the glass particles because that just atomizes them and moves them into the air so you’re breathing them. Put on gloves, pick up the bigger chunks of glass and put them in a sealable plastic bag. Then get a damp paper towel and clean up the remains of the glass you can’t pick up. The wet towel will get all the residual pieces of glass and mercury. Put the paper towel and the plastic bag in the garbage.

Related: How to Dispose of Light Bulbs and 9 Other Hazardous Items

Dear John: I’ve noticed that when a CFL bulb burns out, it may smoke or blacken. Is that dangerous?

People have to change their perception of how a light bulb burns out. The end-of-life period for CFLs is different than what we were accustomed to with incandescent bulbs for the last 100 years. You’ve probably come into a room, flipped on a switch, saw a bright flash and thought, “Oh, I burned out a light bulb.” A CFL does not burn out that way — there is no flash.

The old incandescents were just two wires going into the filament inside the base of the glass. But in the base of a CFL and LED, there are a number of electronic components — transistors, diodes, a circuit board. And if any of them go bad, your light bulb doesn’t work.

You might experience something that has scared many consumers — a little smoke coming out of the CFL, blackening of the base or the smell of something burning. As a consumer, naturally, this tells you something is wrong. But UL has investigated more than 100 of these incidents and found it’s actually not dangerous.

Though manufacturers have taken great strides to change this in the last few years, these bulbs last many years, and the oldest ones are just starting to burn out. The newer ones don’t exhibit that much of the smoke and the blackening.

Dear John: Do CFLs work with light dimmers?

CFLs can work with dimmers if they are rated to do so and you have a (UL approved) dimmable light switch that is for CFL lighting. Look carefully at the compatibility recommendations on the packaging.

Related: CFLs and 8 Other Things You Probably Didn’t Know You Can Recycle

Angela is a Pulitzer Prize-winning digital editor with more than 15 years of experience delivering news and information to audiences worldwide. Prior to joining SafeBee, she was the features editor for at The Boston Globe, overseeing health, travel, entertainment, business and lifestyle coverage. Before moving to features, she was the news and homepage editor, covering stories such as the Boston Marathon bombing, Red Sox World Series victories, presidential elections, a papal inauguration, and more. Her favorite safety tip: Clean your phone! The average cell phone has 18 times more germs than the toilet handle in a men’s restroom.