Q: What compact fluorescent light bulb do I buy to replace a 60-, 75-, 100- or 150-watt regular bulb?

While a regular (incandescent) light bulb uses heat to produce light, a fluorescent bulb creates light using an entirely different method that is far more energy-efficient – in fact, 4-6 times more efficient. This means that you can buy a 15-watt compact fluorescent bulb that produces the same amount of light as a 60-watt regular incandescent bulb. Plus fluorescent light bulbs last up to 13 times longer and use 2/3 to 3/4 less electricity than incandescent bulbs with similar lumen ratings.

Here are the watts needed by regular incandescent bulbs and compact fluorescent bulbs to produce the same amount of light.

  • 20 watts incandescent = 5 watts compact fluorescent
  • 28 watts incandescent = 7 watts compact fluorescent
  • 36 watts incandescent = 9 watts compact fluorescent
  • 40 watts incandescent = 10 watts compact fluorescent
  • 52 watts incandescent = 13 watts compact fluorescent
  • 60 watts incandescent = 15 watts compact fluorescent
  • 75 watts incandescent = 20 watts compact fluorescent
  • 100 watts incandescent = 26-29 watts compact fluorescent
  • 150 watts incandescent = 38-42 watts compact fluorescent
  • 250-300 watts incandescent = 55 watts compact fluorescent
Q: How does a compact fluorescent light bulb work?

Fluorescent light bulbs (including compact fluorescents) are more energy-efficient than regular bulbs because of the different method they use to produce light. Regular bulbs (also known as incandescent bulbs) create light by heating a filament inside the bulb; the heat makes the filament white-hot, producing the light that you see. A lot of the energy used to create the heat that lights an incandescent bulb is wasted. A fluorescent bulb, on the other hand, contains a gas that produces invisible ultraviolet light (UV) when the gas is excited by electricity. The UV light hits the white coating inside the fluorescent bulb and the coating changes it into light you can see. Because fluorescent bulbs don’t use heat to create light, they are far more energy-efficient than regular incandescent bulbs.

Q: Can I use a compact fluorescent light bulb with a dimmer switch?

To use a compact fluorescent bulb on a dimmer switch, you must buy a bulb that’s specifically made to work with dimmers (check the package). GE makes a dimming compact fluorescent light bulb (called the GE Longlife Plus Soft White Energy Saving Bulb) that is specially designed for use with dimming switches. We don’t recommend using regular compact fluorescent bulbs with dimming switches, since this can shorten bulb life. (Using a regular compact fluorescent bulb with a dimmer will also nullify the bulb’s warranty.)

Q: Can fluorescent lamps be put on a dimmer?

Yes, only if the fluorescent light is using a dimmable ballast. Any time a dimmable ballast is used, a compatible dimming switch needs to be installed. The ballast manufacturer can provide a list of compatible switches

Q: Why do fluorescent lamps need a ballast?

Fluorescent light bulbs need a ballast because they use a gas to create light. When the gas is excited by electricity, it emits invisible ultraviolet light that hits the white coating inside the fluorescent bulb. The coating changes the ultraviolet light into light you can see. (Because fluorescent bulbs don’t use heat to create light, they are far more energy-efficient than regular incandescent bulbs.)

The combination of gas, electricity, and coating in a fluorescent bulb is so effective at producing light that, without something to regulate the electricity flowing into the bulb, the light will continue to gain intensity until the bulb stops working. That’s where a ballast comes in. It supplies the initial electricity that creates the light, and then it regulates the amount of electricity flowing through the bulb so that the right amount of light is emitted.

Q: I can’t find the lumen rating on my MR16/MR11 lamp. Why?

MR11s and MR16s are a directional light source, and are only measured by center beam candle power, which is the average amount of luminous intensity, or how bright the light is, at the center of the beam.

Q: Why do halogen bulbs last longer than incandescent?

The life of incandescent and halogen light bulbs, referred to as tungsten filament lamps, is limited by the state of the filament. The filament is the wire inside the bulb that produces light when heated. The light bulb will not work if the filament is broken which may occur as a result of the application of force, such as dropping the bulb, or by lack of tungsten in a particular area over the filament. During the operation of tungsten filament light bulbs, tungsten from the filament evaporates into the gas inside the light bulb. When the tungsten comes in contact with a cool surface it will condense. Often, with incandescent products, the tungsten condenses on the bulb wall. Because the tungsten is redeposited on the wall instead of the filament, the filament grows thin over time. Eventually, there will be a point on the filament with so little tungsten that the filament will break and the light bulb will stop working.

Halogen light bulbs have a special gas inside their bulb containing halogens. The halogen gas facilitates the “halogen regenerative cycle” which means that the halogens carry the evaporated tungsten back to the filament instead of allowing it to deposit on the bulb wall. By placing the tungsten back on the filament instead of the wall, it delays the filament breaking due to lack of tungsten. Although the halogen cycle significantly increases the life of the light bulb, it cannot last forever because the halogen gasses cannot place the tungsten on a specific spot on the filament to avoid any place having too little tungsten and breaking.

Q: What is a halogen bulb?

Halogen is a type of incandescent lamp. It has a tungsten filament just like a regular incandescent that you may use in your home, however the bulb is filled with halogen gas. When an incandescent lamp (one which produces light by heating a tungsten filament) operates, tungsten from the filament is evaporated into the gas of the bulb and deposited on the glass wall. The bulb “burns out” when enough tungsten has evaporated from the filament so that electricity can no longer be conducted across it. The halogen gas in a halogen lamp carries the evaporated tungsten particles back to the filament and re-deposits them. This gives the lamp a longer life than regular A-line incandescent lamps and provides for a cleaner bulb wall for light to shine through.

Q: How much heat (or infrared radiation) is emitted by regular, halogen, and compact fluorescent light bulbs?

Because incandescent and halogen bulbs create light through heat, about 90% of the energy they emit is in the form of heat (also called infrared radiation). To reduce the heat emitted by regular incandescent and halogen light bulbs, use a lower watt bulb (like 60 watts instead of 100).

Fluorescent light bulbs use an entirely different method to create light. Both compact fluorescent bulbs and fluorescent tubes contain a gas that, when excited by electricity, hits a coating inside the fluorescent bulb and emits light. (This makes them far more energy-efficient than regular incandescent bulbs.) The fluorescent bulbs used in your home emit only around 30% of their energy in heat, making them far cooler.

Q: How is lamp diameter measured? How can I determine the diameter of the lamp from the lamp name or description?

The shape of a bulb is followed by its maximum diameter, expressed in eighths of an inch. For example, a R40 has a maximum diameter of 40 eighths of an inch which equals 5″.

The chart below will help you to quickly make these conversions.

Eighths of an inch – Inches

1 – 0.125 11 – 1.375 21 – 2.625 31 – 3.875
2 – 0.25 12 – 1.5 22 – 2.75 32 – 4
3 – 0.375 13 – 1.625 23 – 2.875 33 – 4.125
4 – 0.5 14 – 1.75 24 – 3 34 – 4.25
5 – 0.625 15 – 1.875 25 – 3.125 35 – 4.375
6 – 0.75 16 – 2 26 – 3.25 36 – 4.5
7 – 0.875 17 – 2.125 27 – 3.375 37 – 4.625
8 – 1 18 – 2.25 28 – 3.5 38 – 4.75
9 – 1.125 19 – 2.375 29 – 3.625 39 – 4.875
10 – 1.25 20 – 2.5 30 – 3.75 40 – 5