Light Wattage: Bulb Wattage, Lumen, CRI & Voltage

Whenever you are choosing any lighting bulb, you should consider wattage, lumen, CRI, and voltage amongst others. This guide explores all fundamental aspects of light wattage.

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Last updated on February 14th, 2024 at 07:55 pm

What Is A Light Wattage

The energy load required to generate a certain amount of light is called light wattage. A higher light wattage translates to higher energy consumption. Also, light wattage dictates the amount of heat emission from a light bulb.

What Is Watt?

Watts, in this case, is a measure of how much energy a light source consumes. Alternatively, watts can be defined as the units used in measuring electrical power.

Watts is the unit used in rating the power of various electrical components. Mathematically, you can calculate watts as below:

Voltage (in volts) x Current (in amps) = Power (in watts)

Light Wattage Vs Lumen

Many times, wattage is used interchangeably with lumens. However, this should not be the case.

We will help you break down and point out the difference between the two.

In the proceeding sections, we defined watts (w) as a standard measure of electrical power (one joule

per second).

Fact: The more the watts, the more energy used per second.

On the other hand, Lumen (lm) is the international standard measure for the total amount of visible light

emitted from a source.

Fact: Direct sunlight produces up to 100 000 Lumens.

From the above definitions, you can now clearly see the difference between the lumens and watts.

Yes, they are both standards of measurement. However, one measures electrical power (watts), while the other measures brightness (lumen).

Relationship between Lumens and Light Wattage

The relationship between lumens and wattage will vary across the various lighting technologies. In this

case, we will consider two lighting technologies, incandescent bulbs and LED bulbs.

LED BulbLED BulbTraditional Incandescent BulbsTraditional Incandescent Bulbs

From the above table, you can see that the type of lighting technology does dictate the number

of watts required to produce specific lumens. Generally, the LED bulb requires less wattage to

attain higher brightness levels.

Fact: LED can produce up to 110 Lumens per watt.

In summary, the relationship between the lumens and wattage dictates the light bulb’s energy

efficiency vis-à-vis its brightness.

Importance Of Knowing Light Wattage

Choosing a bulb with the correct wattage for your intended application is essential. Below are the main reasons why you need to comprehend light wattage.

To Preserve The Bulb’s Life

If the fixture’s wattage is higher than the bulb’s wattage, the bulb is likely to malfunction or burn out prematurely.

For Your Safety

Using a bulb with a lower voltage rating than the fixture can potentially cause a fire outbreak. If the bulb overheats due to excess energy from the fixture, it can explode, causing a fire outbreak.

To Prevent Over Lamping

Over lamping occurs when you use a bulb with a higher wattage than the electrical fixture. Over lamping will ultimately burn the cables or destroy the entire electrical fixture.

In the long run, using a bulb with incorrect wattage is costly. A detailed understanding of a bulb’s light wattage is essential in cutting costs and using the bulb efficiently.

Tip: Always check your electrical fixture’s rating before purchasing a light bulb.

       Ensure you confirm the manufacturer’s wattage rating for the bulb.

Relationship Between Light Wattage And Bulb Energy Consumption

The higher the bulb wattage, the more the bulb energy consumption.

From its definition, wattage is the amount of energy consumed by a light source. Deductively, the higher the light wattage, the more electrical energy the light source will consume.

However, this does not imply that the high watts translate to brighter light sources.

Fact: High Light wattage = High Bulb Energy Consumption

Average Light Wattage For A Bulb

The average light wattage for a bulb depends on the bulb type. Below are the common types of bulbs and their average wattage.

  • Incandescent Bulb – 60 to 80 Watts
  • CFL Bulb – 14 to 20 Watts
  • LED Bulb – 7 to 10 Watts

How Light Wattage Affects Light Intensity

The light intensity can also be referred to as light output or brightness. Lighting wattage does not affect the light intensity of all bulbs.

In incandescent light bulbs, the light wattage will directly affect the light intensity. The higher the wattage, the higher the light intensity. For example, a 100-watt incandescent bulb will produce about 1700-1800 lumens.

Notably, a 32-watt CFL or a 15-watt LED is the equivalent of 100-watt incandescent bulbs.

Remember, the two types of bulbs have a lower wattage but still produce the same light intensity as an incandescent bulb.

Conclusively, modern bulbs have lower wattage (low energy consumption) but are still offer the same brightness as traditional light sources. Hence the name, energy saver bulbs.

Converting Lumen To Wattage

In an internet era like ours, conversion of a lumen to wattage isn’t an uphill task. Various websites offer online calculators that you can use to convert lumens to wattage.

However, if you are a mathematics enthusiast, you can use the formula below for conversion.

P(W) = ΦV(lm) / η(lm/W)

From the above formula, Power (P in watts) is equal to the luminous flux (Φ in lumens) divided by the luminous efficacy (η in lumens per watt).

Luminous efficacy means the number of lumens per watt. Notably, energy-saving bulbs have more lumens per watt. Consequently, they have a lower wattage but a higher light intensity.

Light Wattage As A Measure of Brightness

In the past, it was assumed that the more the wattage, the brighter the light source. However, this narrative has been revised with the advent of low-energy lighting technologies.

Brightness is defined as the light output or the amount of light emitted by a light source. The unit for measuring light output is lumens and not wattage.

Fact: Wattage is gradually being phased out as a measure of brightness.

How Light Wattage Affects Choice Of A Light Bulb

Light bulb wattage will affect the choice of a bulb in terms of energy consumption. Light energy will guide you in choosing a light bulb that will:

  • Suit your electrical fixture.
  • Conserve energy.

Notably, you can also use wattage to gauge the brightness of the bulb if you know the luminous efficacy of the bulb.

Difference Between Incandescent Light Bulb, CFL, and LED Wattage

The different types of bulbs have varying wattage. Below, we briefly discuss the wattage of the various bulb types.

LED Lights Wattage

LED bulbs have the least amount of wattage. Typically, the wattage of LED lights ranges from 7.5 watts to 17 watts.

CFL Wattage

Compact Fluorescent Bulb has the second least wattage ranging from 5 watts to 20 watts.

Halogen Light Bulb

The wattage range of a halogen bulb is from 18 watts to about 70 watts.

Incandescent Light Bulb

Lastly, traditional incandescent bulbs have the highest wattage ranging from 25 to 100 watts.

Notably, the above bulb types are arranged in descending order regarding luminous efficacy. LED lights have the highest luminous efficacy, while incandescent bulbs have the lowest luminous efficacy.


What Is Color Rendering Index?

Color Rendering Index (CRI) measures how light affects your vision of color; or the appearance of a specific color.

CRI will affect how the surrounding of the light source will look. Color rendering is measured using a scale chart ranging from 0 to 100. The closer the rating is to 100, the more accurate the color rendering of the light bulb will be.

Is There a Relationship Between Color Temperature And Wattage Of Lighting systems?

Color temperature is the measure of how blue or yellow the color light emitted from a bulb is.

Light sources with a blue color temperature tend to be cool. Conversely, the yellow color temperature implies the bulb is warm.

Most blue color light bulbs are either LED or fluorescent light bulbs. On the other hand, incandescent bulbs are categorized as warm light sources and hence have a yellow color temperature.

Conclusively, it is evident that bulbs with higher wattage (incandescent bulbs) have a yellow color temperature while those with low wattage have a blue temperature.

What is a Low Wattage Light Bulb?

Between 4 watts to 15 watts are low wattage bulbs. However, anything below 40 watts is a low wattage bulb. These bulbs save significant energy costs.

Useful Resources:



Luminous Flux

Color Rendering Index

Light Color Temperature

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  1. David Meade Reply

    Above you say “Using a bulb with a lower wattage than the fixture can potentially cause a fire outbreak.”

    Isn’t it more correct to say that using a bulb with a lower VOLTAGE rating than the circuit could cause a fire outbreak? E.g., if you plug a 110-volt bulb into a 220-volt circuit, you will blow out the bulb. On the other hand, if you plug a 220-volt rated bulb into a 110-volt circuit, the bulb would light only dimly. I don’t believe that the wattage rating of the bulb matters…it’s the voltage rating.

    1. admin Reply

      Sure, thank you David. Voltage rating matters.