Understanding Lumens to Watts Conversion in LED Lights: Intensity and Brightness Explained

Brightness and intensity are among the major features of LED lights. These properties are influenced by Lumens and Watts. Understanding these metrics helps you understand the quality, performance, and lifespan of an LED. This article explores the two metrics, how they are calculated, their significance, and more.

Overview of Lumens and Watts

Learning the definition of these concepts is the best way to understand them. As you will realize, they are closely related. However, each stands for a specific aspect of LED lights that is quite significant. 

What are Lumens (lm)?

Lumens are a metric of light that indicates the light intensity emitted by a light-emitting device, such as an LED. Light intensity is also referred to as luminous flux, which means the quantity of visible light emitted over a quantifiable period.

Lumens are expressed as lm and they are tied to the amount of power (Watts) that the light consumes to generate light. For instance, a 60-Watts LED light could generate light of 1000 lumens.

In most cases, the higher the lumens, the brighter the light source. That also means the device consumes a lot of power in Watts.

Put simply, lumens are the SI units of illumination. They indicate the brightness level of a light source. While there are special tests to determine the brightness of light, the light intensity is primarily the perceived power of light. That is why light intensity is expressed as the amount of visible illumination.

What is Watts (W)?

Light sources require various forms of electric energy to produce light. This energy is measured in Watts. In the light generation process, various light sources generate electromagnetic energy referred to as radiant flux. Radiant flux represents the energy consumed over a specified time.

The energy consumption of small devices such as LEDs is denoted by Watts, while for larger devices is represented by Kilowatts (Kw). Wattage measurement can be expressed by the rate of energy transfer per unit of time. In this case, 1 Watt is equivalent to 1 Joule per second (1W = 1 J/s). 

Quantifying the rate of transfer over time is essential to understand the amount of energy an LED source would consume over time. When purchasing an LED-powered device, such as an LED panel, you would not have to worry since the manufacturer indicates the Wattage ratings. 

Watthours is another essential metric used to quantify the amount of energy consumed by an electrical device, such as an LED, over time. This metric is measured in kilowatthours (kWh), which represents the amount of Watts consumed over an hour. It helps you identify the amount of energy consumed by the light.

In context, the amount of energy consumed is the multiple of Wattage ratings by the consumption time. For instance, a 50-Watt LED bulb that lights up for 5 hours consumes 250 kWh of energy.

How to calculate lumens and watts 

Lumens and Watts are calculated using various formulas. These formulas depend on factors such as the type of light and source of energy. Since both metrics are intertwined, they have influence over each other.

Calculating Lumens

Electrical devices that generate light or illumination are referred to as luminaires. Luminous flux is a better measurement of light intensity since it takes into account variables like the directional nature of light. Luminous flux is a far more accurate indicator of the light intensity of LED lights since LEDs generate a unidirectional light.

Unidirectional light is mainly measured in lumens using the following formula;

Φ = I × A × K

  • Φ is the universal symbol for luminous flux
  • I represent the luminous intensity, expressed in Candelas
  • A is the beam angle that the light illuminates
  • K is a coefficient that indicates the efficiency of a light source to illuminate light in a certain direction 

With these values, the Lumens or luminous flux of a light source can be determined and noted. This is one of the factors you should look at when choosing LED-lighted panels or generally LED lights.

Calculating Watts

Most light sources use electrical energy as their source of power. Power has both strength (Amperage) and pressure (Voltage). These two properties will vary depending on the energy outlet and the target device.

Power, in this case, Watts, is calculated using the following formula;

P = V × I

  • P is power in Watts
  • V is voltage
  • I is current in Amperes 

Voltage and Amperes are dynamic in that they depend on factors such as the source of power and its flow path. This boils down to the engineering of the luminaire and the power supplier. LED lights are optimized to be effective power consumers. As such, they are known to be among the best luminaires in the market.

Understanding luminous efficacy (lm/W)

There are many factors used to determine the efficiency of a light source in relation to its light intensity versus its power consumption. Luminous efficacy is used to describe this property. It is an expression of luminous flux over Wattage.

In other words, luminous efficacy is the lumens per watts efficiency. It measures the efficiency of a light source to convert power (Watts) into light (Lumens). 

If a light source needs too much power to produce light, it is probably inefficient. On the other hand, there are lights with high Wattage ratings that do not consume too much power. LEDs are a great example. This happens because LED technology is optimized to produce a lot of light without needing too much power.

The luminous efficacy of LED lights can go up to 300 lm/W. This range shows that LED luminaires are more effective in terms of lighting. Therefore, when buying an LED-lighted device, choose the one with high luminous efficacy for better results.

Significance of lumens and watts 

You might be wondering why is it important to understand lumens and watts. The following are some of the many reasons why you should.

Importance of lumens

Lumens or luminous flux has several purposes. Apart from being a standard practice in photometry, there are many concerns taken into account when choosing lights. Mainly, you will consider the costs and environmental impact of lighting sources. These can be summarized as follows;

  • Indicating levels of brightness

We started by noting that lumens are a measure of the brightness levels of a lighting source. This is important in several ways. The level of brightness is a factor used to determine if the light emitted will be sufficient. This is dependent on the illumination area or solid angle. While the illumination area applies to light bulbs, the solid angle applies to LED panels.

  • Standardizing light output

Finding a common unit to measure light is another significance of lumens. There are international organizations that regulate lighting. Their mandate is to develop measures to regulate lighting, among other agendas. 

Standardizing lighting entails objectives like stipulating when lighting is misused. For instance, issues like light pollution can arise when these objectives are not enforced. Overly bright light sources lead to light pollution, especially in outdoor environments. Therefore, denoting the Lumens of a light source can help you avoid causing light pollution

Importance of watts 

Energy consumption should and is a major concern across the board. This means lighting solutions need to be efficient power consumers. When that is the case, there are several benefits that arise. They include;

  • Regulating power consumption

Lighting is estimated to consume between 20 – 50% of electrical energy supplied to commercial buildings. It means that regulation is vital when such a huge portion of power is dedicated to one category. Opting for energy-efficient lighting solutions like LEDs will ensure that the total energy consumption is reduced. The less the Wattage, the higher the energy savings.

  • Identifying efficient lighting solutions

Lighting solutions manufacturers are legally required to accurately indicate the Wattage ratings of their products. This helps you identify the suitable rating according to your lighting requirements. Also, since low ratings imply high savings, you will have an easy time picking out efficient lighting solutions.

  • Cost considerations 

Wattage is among the factors that influence the cost of luminaires. Generally, the more efficient the lights are, the higher their costs. This is why incandescent lights are usually cheaper compared to alternatives like LEDs. Luckily, advancement in technology has standardized the manufacture of LED lights and made them more affordable.

Lumens to watts conversion 

Total energy consumption and lighting requirements are the top factors considered when choosing luminaires. Even though the two are distinct properties, people convert lumens to watts when making buying decisions. 

This conversion is observed since most people are more familiar with watts than with lumens. They believe wattage is a direct indicator of light intensity. As inaccurate as this is, the belief is widespread. Still, the errors are minimal in situations where lighting technologies are related. 

Traditional lighting technologies require high watts to produce the same amount of light intensity as modern counterparts. In this regard, a 7:1 ratio is used when converting lumens to watts. This ratio means that 1 watt is equivalent to 7 Lumens. 

In other words, for every 1 watts of energy, the light intensity is estimated as 7 lm. This approach helps buyers estimate the amount of energy that will be consumed by an incandescent light as well as the level of brightness.

This simple table will explain further;


Watts Lumens
50w 350lm
80w 560lm
100w 700lm
120w 840lm


The table shows that each Lumens is 7 times the Wattage. As you can tell, this conversion will primarily apply to incandescent and other non-modern lights. This is because most modern lights have lumens and wattage ratings clearly indicated.

Light intensity and brightness units of measurement

The brightness and intensity of light are informed by many metrics apart from Lumens and Watts. These metrics are expressed as photometric values and they can be influenced by several factors. Some of these metrics include;


The luminous flux of a light source is quantifiable. Lux is a unit of measurement used to denote the total amount of light intensity or illuminance of a light source. The quantity of illuminance is calculated based on the surface area of the lighted crosssection. 

Lux differs from lumens in that Lumens measures the light intensity, regardless of the surface area of the lighted area. In other words, Lumens is a measure of illuminance in all directions. The amount of lux depends on the distance of the light source to the area being measured. That is why panels look brighter when looked at from a short distance.


This is another common measure of brightness. It is particularly used to describe the brightness of display screens. Nits are units of measurement. These units are expressed as candela per square meter. Candela is the luminous intensity, while the area per square meter represents the brightness according to the size of the display.

The higher the nits value, the higher the brightness of the screen. Therefore, whereby lumens indicate the total amount of brightness, nits indicate the light according to the display size.

Candela (cd/m²)

This unit of measurement is used to denote the luminous intensity of light. It is the international SI unit and it is measured in square metres. Light intensity is measured in relation to the direction of light. Candela applies to LED lights because they are known to be unidirectional in nature.


Did you know that Candela is a Latin word for candles? While candela is the measure of light intensity in square meters, footcandle is the measure of the same property, but in feet. It is actually in its name— foot candle.

The expression formula for footcandle is;

1 footcandle = 1 lumen/ft² 

Footcandle can be used interchangeably with nits or candelas. The difference comes in when factors such as direction, surface area, and light source are taken into account. 

Pupil Lumens (Plm)

When measuring luminous flux, the color perception of the human eye is not considered a variable. Therefore, pupil lumens (Plm) were adopted as a unit to measure lumens and to address this issue. Pupil lumens measure the perception of the brightness of the light.

Benefits of Measuring the Light Intensity and Brightness

There are many reasons you should care about the brightness and light intensity of a light source. Here are some of these reasons;

Helps in Decision-Making

Light intensity and brightness are among the factors you will contemplate when deciding on the type of light to purchase. Since the two are controlled and denoted by lumens and watts, you can make decisions based on the corresponding units of these metrics.

For example, you would not purchase a high-wattage light since you already know that it implies high power consumption. Still, you would not entirely rule it out since there are high-wattage lights that have power-saving technologies. In other words, you would use luminous efficacy to make the final decision.

Energy Efficiency

In a world where energy crises are a growing concern, it helps to be mindful when dealing with heavy power consumers such as lights. Being aware of these concerns is the first step toward addressing the problem.

Mindfulness involves compromising brightness levels since you will be saving on energy consumption. It also entails choosing better lighting solutions like LEDs since they are better energy savers. All these and more are recommended by environmental protection agencies like EPA.

Alleviate Light Pollution

Too much brightness leads to light pollution. This is a case whereby there is too much artificial light intensity. You will find this kind of pollution mostly in urban centers. Light pollution has the negative effects of disrupting natural cycles, increasing CO₂ gas emissions, and so on. 

The chances of contributing to light pollution are lowered when one is aware of the luminous flux of a light source. It will help people choose luminaires that will shine enough light to illuminate without causing spillovers.

Lighting Design 

When picking out lights, you are most likely to be guided by a certain design. This is the basis of lighting design. It is a concept in architecture that explores how light fits in a given space. Aspects like light intensity and brightness are huge factors in lighting design.

With these properties, you will be able to choose luminaires with the right values to support your design. An example is choosing lights that have high brightness in case the lighting design demands well-lit spaces.

Avoid Lumen Depreciation

Over time, the quality of luminaires drops significantly. Luminous flux is one of the key aspects that is affected by age. In other words, lights experience what is known as lumen depreciation. This aspect is primarily experienced in LED lights. As LEDs age, their ability to maintain brightness decrease significantly. 

LM-80 is a standard measure used to test the lumen depreciation and color shift of LED lights. It tells how long LED lights can sustain without their color changing or becoming dimmer. 

These properties are affected by various external and internal issues. Apart from age, lumen depreciation is contributed by heat and the quality of LED lights. Color shift on the other hand is affected by degradation of phosphor, environmental stressors, and other underlying conditions. Mitigating these issues beforehand is beneficial,

How Lumens and Watts Influence the Cost of LEDs

Currently, Light Emitting Diodes (LEDs) are among the most common and widely used luminaires in the market. However, they are not cheap, especially when used in display technologies. Lumens and watts contribute to the cost of LEDs in the following ways.

Energy consumption 

LEDs consume energy in watts and convert it into lumens. The amount of energy consumed is tied to the electromagnetic properties of the LED. This means if the electromagnetic properties are advanced, the light is likely to require less energy to get illuminated, and vice versa.

LED lights with low wattage requirements are generally more expensive. This is because they have a negligible impact on utility bills. For light bulbs, they are much cheaper since there are several efforts toward the adoption of energy-efficient lighting solutions.

Maintenance costs

Costs associated with the regular operations of LEDs are minimal. This is because LED lights have a long lifespan. For instance, inorganic LEDs such as micro LEDs can maintain their luminous flux for up to 50,000 hours. This eliminates the need for regular maintenance which can be costly.

Minimal maintenance practices translate to low operational costs for LED lights. However, this only applies if the quality of LED lights used is high. There are formulations that tend to require regular maintenance. 

Upfront costs 

The cost of LED lights will be impacted by their luminous flux (Lumens) and Wattage. As discussed earlier, high watts mean high power consumption. An LED with high wattage requirement could be lacking energy-saving technology. High wattage does not necessarily result in high illuminance. These LEDs end up being a lot cheaper.

Impact on the environment

There is a huge price to pay for a dilapidated environment. Environmental activists, led by scientists, agree that there is a need to focus more on preventing issues like global warming when there is still time.

LED technology has proved to be a better alternative lighting solution that has a minimal carbon footprint. Due to this, LEDs have gradually become cheaper to accommodate more takers. Provided that lighting is an integral part of human lives, LEDs will contribute to a better tomorrow for the future.


Light has many defining properties. In this article, we discussed two of the main ones — brightness and light intensity and their corresponding metrics. The article established that LED lumens and wattage significantly impact these properties. Doing so helps you choose the right lighting source according to your needs.

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