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What to Consider When Choosing a Light Bulb

Revised: 7/30/19
Grainger Editorial Staff

While a light bulb’s function is fairly simple, choosing a light bulb is anything but. There are so many options available that it can seem overwhelming. Rather than buy a bulb that appears to fit, take the time to figure out which bulb is the right match for your fixture. Here's what you need to know about which light bulb to buy:
5 Factors to Consider When Choosing a Light Bulb

1. Light Bulb Shape and Base

Shape: Light bulbs tend to be described by their designated shape name, such as globe, reflector or spiral. Light shapes are denoted with a letter-number-letter. The first letter indicates the bulb’s shape; the number is the bulb’s diameter at its widest part while the last letter designates bulb length.

Base: There are two main types of light bulb bases: pin base or screw base. It is important to see which base is most suited to connect to the socket or ballast of your lighting source. Choosing the correct bulb base type is vital along with its size to ensure compatibility with a fixture. Consider the shape of your light bulb to make sure it will fit and function properly in the fixture.

2. Watts and Lumens

Watts measure the amount of energy required to light the light bulb, whereas lumens measure the amount of light produced. The more lumens produced by a light bulb, the brighter the light. When selecting an energy-efficient light bulb, look at the lumens, rather than watts.

3. Color Rendering Index (CRI)

Color rendering describes how a light source makes the color of an object appear to the human eye. The CRI is a scale from 0 to 100 percent indicating how accurate a "given" light source is at rendering color when compared to a "reference" light source; a typical comparison is to daylight. Light sources with a CRI of 85 to 90 are considered good at color rendering. Light sources with a CRI of 90 or higher are excellent at color rendering and should be used for tasks requiring the most accurate color discrimination.

4. Color Temperature

Color temperature is measured in degrees Kelvin (K). The color temperature of a light bulb describes how the light appears when an illuminated bulb is looked at directly by the human eye.Light bulbs that produce a yellowish white light may have a color temperature around 2700K, producing a “warm, cozy feeling.” As the color temperature increases, the yellowish color of the bulb decreases, and the white or “cooler” color increases. At 5000K or higher, the light color appears bluish white.


2700K 3000K 3500K 4100K 5000K 6500K
Light Color Warm/Soft
Warm/Soft White Cool, Bright White Cool, Bright White Daylight or Natural Daylight or Natural
Mood Created Ambient Personal Calm
Friendly Inviting Precise
Daylight Vibrant Daylight
Uses Commercial Hospitality Commercial Hospitality Light Commercial Garage Commercial Commercial


5. Voltage

For maximum efficiency, the voltage on the light bulb should match the supplied voltage of your fixture. It’s important to be as precise as possible with voltage as low voltage draws more current and high voltage can reduce the life of your bulb. In the case of incandescent light bulbs, you can use a lower voltage light bulb but it will emit lower light levels as a result.

As simple as light bulbs are functionally, don’t let choosing one confuse you. If you take into consideration the factors above, your fixtures and the area you want to light, you can’t go wrong when choosing the right light bulbs.


Lumen Coalition

The information contained in this article is intended for general information purposes only and is based on information available as of the initial date of publication. No representation is made that the information or references are complete or remain current. This article is not a substitute for review of current applicable government regulations, industry standards, or other standards specific to your business and/or activities and should not be construed as legal advice or opinion. Readers with specific questions should refer to the applicable standards or consult with an attorney.


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