Knowledge Base

Despite Thomas Edison not inventing the first light bulb, he did invent the first household light bulb. There is a small rumor that he was afraid of the dark. Thanks to Thomas Edison, everyone today is able to continue their daily tasks into the night without a problem.


Incandescent lights use a specialized resistor that slows down the electricity that flows through it. Some of the electrical energy is given off as light, but a lot is given off as heat, which is why these bulbs are not as efficient. The bulb must be air tight so the resistor filament does not burn out.

Incandescent light tends to be a warm white color, mostly because its light wavelengths pass beyond the visible spectrum and include many infrared wavelengths. This range, including red visible and invisible light, gives it a more natural color. 


Halogen bulbs are a more efficient version of the incandescent bulb. These bulbs emit very bright white light. Their light output will not diminish as the bulb ages. Halogen bulbs are also known for their consistent ability to start up with no flickering.


Fluorescent lights use a special inert gas and a powder coating on the inside of their bulbs to produce lights. The electrical current cycles through the gas and excites its atoms. After each cycle the atoms release their energy in small bursts, which then hit the atoms of the powder coating. The coating atoms react in the same way, but the energy they release is actually light. This process uses electricity very efficiently.

Fluorescent lights tend to be white or bluish, but their color depends on the temperature of the light produced, with light around 6500 Kelvin produced wavelengths across the spectrum in a way similar to daylight.


Light-emitting-diode, or LED, bulbs are long-lasting and extremely energy-efficient. LEDs use a semiconductor as their light source, and the amount of light given off is measured in lumens. Incandescent bulbs are categorized by their wattage, but wattage does not measure brightness; it only indicates how much electricity a bulb uses. LED lighting has many applications and may replace other types of lighting in the future. Battery-operated LED lanterns or flashlights have several advantages over other types of lighting, such as incandescent bulbs. Widespread use of LED lighting, however, may require a reduction in cost.


Incandescent light bulbs fade with age, unlike halogen bulbs. An average incandescent bulb will last anywhere between 750 and 1,000 hours. An average halogen bulb will last anywhere between 2,250 and 3,500 hours. A 75 watt incandescent bulb produces around 1,180 lumens of light while a 75 watt halogen bulb lets off about 1,300 lumens. Both incandescent and halogen light bulbs are available in a variety of sizes and voltages.

LED bulbs are expensive, costing more than 10 times the price of equivalent incandescent bulbs. Because LED bulbs use less energy and last longer, however, they save money compared to incandescent or compact fluorescent bulbs in the long run. Energy Star-designated LEDs are a good investment, and prices for LEDs are expected to come down in the future, encouraging more LED bulb use.


Standard incandescent light bulbs are great for everyday use in the home where “soft” light is desired. Some incandescent light bulbs are used not only for their light output but for their heat output as well. Heat lamps found in reptile tanks utilize the heat producing capabilities of incandescent bulbs to warm small, contained environments. Halogen bulbs keep a constant light output throughout their lives which is one of the reasons why they are widely used in car headlights. This type of bulb is ideal for outdoor situations like lighting up a deck or patio. Halogen lights can also be used in the home where intense light is desired.


While there is no simple conversion formula, LED bulbs tend to be more energy efficient than incandescent bulbs at lower levels of brightness than they are at higher levels of brightness. For example, to produce 450 lumens, an LED bulb needs 4 or 5 watts and an incandescent bulb requires 10 times as much energy -- 40 watts. Yet to produce 2,600 to 2,800 lumens, an LED bulb needs 25 to 28 watts and an incandescent bulb requires about six times more energy --150 watts.

How to Compare LED Light Output to Incandescent Bulbs

Changing a light bulb is one of the simplest steps most households can take to save energy. According to Energy Star, if each household changed just one bulb, the reduction in greenhouse gas emissions would be the equivalent of taking 2 million cars off the road. Light-emitting diodes are one of the many energy-saving alternative lights now available. Although expensive, these bulbs save you money by lasting up to 20 years and using only a fraction of the energy that an incandescent light does. Shopping for LEDs can be confusing until you learn how to compare their light output compared to other bulbs.

Understand what is meant by lumens. Traditional bulbs are measured in watts, but because LEDs use so little energy, wattage is not an indication of brightness. Lumens are a measure of brightness and are now stated on most packages of bulbs.

Determine the wattage on your current bulbs. Before you purchase LEDs to replace your incandescent bulbs, you'll need to know the wattage of your old bulbs. This number is printed either on the top of the bulb or along the base of the bulb.

Convert your old bulb's wattage into lumens. This can be calculated if you happen to know your bulb's lumens per watt, using this equation: Lumens = Watts x lumens per watt. However, because lumens per watt vary for both incandescent and LED lights, it's easier to use a wattage-to-lumens comparison chart. Since most household bulbs are 40W, 60W, 75W or 100W, you may be able to memorize their equivalent lumens. Some of the common wattages vs. lumens for incandescent bulbs are: 40W equals 450 lumens, 60W equals 800 lumens, 75W equals 1100 lumens and 100W equals 1600 lumens.

Examine the label of the LED bulbs at the store. Bulb packaging now has a Lighting Facts label to inform you about the bulb's lumens, wattage used, lifespan and cost to operate. Lumens are listed under Brightness. Find a bulb that matches the lumens you need to replace your incandescent bulbs.


Most incandescent bulbs emit a warm, yellow light, while most LEDs produce a white light. If this is a concern, check the Lighting Facts label for the Light Appearance information.

Look for Energy Star approved LEDs. These lights produce a high-quality light over their lifetime and are more reliable than nonapproved LEDs.


Never exceed the maximum wattage stated on your light fixture.

Light Bulb Shapes Guide

The names of light bulb shapes are denoted with a letter, which describes the shape, and a number, which indicates the size. The number associated with the shape indicates the diameter of the light bulb at its widest part in eighths of an inch. For example, an A19 light bulb has a maximum diameter of 19/8 of an inch, or 2.375 inches.

lk_shape_aA – Appliance light bulbs

Appliance light bulbs are one of the most widely used shapes and can be used almost anywhere, including homes, hotels, and restaurants. Appliance light bulbs have the shape that most consumers think of when they picture a light bulb. Typical sizes include A15, A19, A21, and A23.

PS – Pear shape light bulbs

Pear shape light bulbs are similar to A light bulbs, except they have a larger diameter, which causes the bulb to look like a pear. Typical sizes include PS30 and PS40. PS30 light bulbs can be found in office buildings and retail stores, whereas PS40 light bulbs are used in radio towers, cellular towers, bridge power lines, and high tension wires.

lk_shape_sS – Sign light bulbs

Sign light bulbs are found in outdoor signs used by casinos, hotels, restaurants, and theatres. Typical sizes include S6, S11, and S14.

lk_shape_cC – Candle light bulbs

C light bulbs are made to look like a candle flame for decorative applications, such as chandeliers, restaurants, bathrooms, and hotels. C light bulbs with a blunt tip are sometimes referred to as “torpedo shaped” or “bullet,” as with most compact fluorescent C light bulbs and C-7 incandescent bulbs. C light bulbs with a molded, bent tip (also known as a flame tip) are sometimes referred to as a “chandelier light bulb.” The bent tip is created in order to give the light bulb a more aesthetic appeal. The C7 is used in marquees, time/temperature signs, and scoreboards. The C9, C11, and C15 are used in decorative applications.

lk_shape_fF – Flame light bulbs

F light bulbs are similar in size and shape to C light bulbs; however, the glass of the bulb is blown and/or etched in such a way that causes the light to look as though it is flickering like a flame. F light bulbs are used in decorative applications such as chandeliers, bathrooms, and restaurants.

lk_shape_hH – Chimney light bulbs

Chimney light bulbs are found in decorative applications such as coach lights and post lights. The most common size is H19.

lk_shape_gG – Globe light bulbs

Globe light bulbs are found in decorative applications, such as bathrooms, theatres, restaurants, and hotels. Typical sizes include G16.5, G25, and G40.

lk_shape_rR – Reflector light bulbs

Reflector light bulbs have a built-in reflecting surface, which causes the light to be pushed through the front of the light bulb, as opposed to being emitted around the entire bulb. Reflector light bulbs are used for down lighting, and they are used primarily in recessed cans or track lighting for residential, retail, hotel, and restaurant applications. The most common size is R20.

lk_shape_brBR – Bulk Reflector light bulbs

BR light bulbs were created in response to EPACT, which mandated that reflector light bulbs needed to meet minimum efficiency standards. Standard reflector light bulbs in higher wattages and sizes lost light in the neck and sides of the light bulb. The bulk reflector in the neck of the light bulb redirects the light lost in the neck and reflects it forward to increase the overall lumen output of the light bulb, allowing light bulb manufacturers to continue producing the larger reflector light bulbs and still abide by EPACT laws. Typical sizes include BR30 and BR40. These light bulbs are used for down lighting in recessed cans for residential, hotel, food service, offices, and restaurant applications.

lk_shape_erER – Elliptical Reflector light bulbs

ER light bulbs were also created in response to EPACT. In this case, the elliptical reflector increases the overall lumen output by redirecting light that has been lost at the sides of the light bulb and reflecting it forward. The most common size is ER30. These light bulbs are used for down lighting in recessed cans for residential, hotel, and office applications.

lk_shape_parPAR – Parabolic Aluminized Reflector light bulbs PAR light bulbs are reflector light bulbs that have an aluminized reflector in a parabola shape. They are covered with a hard glass lens to control the light beam, which is available in a variety of beam spreads from narrow spot to wide flood. PAR light bulbs can be used outdoors unprotected because their hard glass shell can withstand adverse weather. PAR light bulbs are also used for down lighting applications in recessed cans and track lighting in residential, retail, museums, and art gallery applications. Typical sizes include PAR16, PAR20, PAR30, PAR30 long neck, and PAR38. The PAR30 long neck was introduced to replace incandescent BR30 light bulbs in recessed cans in which standard PAR30 light bulbs did not fit.
lk_shape_parMR – Mirror Reflector light bulbs MR light bulbs have a mirrored reflector. They are used for accent and spot lighting in various retail, residential, and commercial applications. The most common size is MR16; however MR11 is also used in limited applications.
lk_shape_tT – Tube light bulbs T light bulbs are shaped like a cylindrical tube. Depending on the size, T light bulbs have very different applications. Incandescent T6 light bulbs are used in exit and stairway signs and picture lights. Linear fluorescent T12, T10, T8, and T5 light bulbs come in a variety of lengths, ranging from 2-8 feet. These light bulbs are placed in fluorescent troffers and are used for general lighting in offices, retail outlets, hospitals, and parking garages. High intensity discharge light bulbs also come in T shapes, including T9 and T15. These light bulbs are used in sports arenas, billboard signage, and industrial applications.
lk_shape_u-bendU-Bend – U-Bend Tube light bulbs The U-Bend T8 is created by bending a 4-foot length T light bulb into a U shape in order to reduce the maximum overall length of the light bulb. This is desirable in some locations that have limited space. By bending a 4-foot light bulb into a U configuration that is comparable to a 2-foot light bulb in length, the end user will receive double the light output in the smaller space. This light bulb is used in offices, hospitals, and retail applications.
lk_shape_spiralSpiral – Spiral Tube light bulbs The spiral light bulb is the shape of a compact fluorescent light bulb. A smaller diameter fluorescent T light bulb, such as T4, T3, T2, or T1, is twisted into a spiral or coil configuration in order to provide the most amount of light output in the least amount of space. Spiral light bulbs are typically used to replace incandescent light bulbs and can be used virtually anywhere, including residential, commercial, retail, hospitality, and restaurant applications.
lk_shape_btBT – Blown Tube or Bulbous Tube light bulbs The blown tube light bulb is a T light bulb that has had the glass blown in the middle so that it appears to have a bubble in the middle of the tube. BT halogen light bulbs can be used to replace incandescent light bulbs. High intensity discharge light bulbs come in BT28, BT37, and BT56. These are used in sports arenas, car dealerships, canopy lighting, and industrial applications.
lk_shape_edED – Elliptical Dome light bulbs

ED light bulbs have an elliptical shape to house the arc tube of a high intensity discharge light bulb. ED light bulbs are used in sports arenas, high bay industrial lighting, parking lots and garages, and car dealerships. Typical sizes include ED17, ED18, ED23.5, ED28, and ED37.