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Lumens to Watts Conversion: A Quick & Easy Guide

What are lumens and watts? How do you convert lumens to watts? What are the formulas needed for lumens to watts conversion? Watts is more common today while lumen is a less popular term. Perhaps these were discussed during grade school science and physics classes. You’ve probably heard of watts more than lumens. Perhaps you might remember going to the hardware store and buying a 15-watt light bulb. But what could be the significance of watts? What does it measure? Moreover, how does the lumen fit into the equation? Are the two related to each other? 

In this article, we’ll answer those questions and provide easy-to-digest information about lumens to watts conversion. Let’s begin.

Defining Lumens

We get it. Lumen kind of sounds technical and uncommon today. However, discussing it is important in understanding lumens to watts. It’s a word you don’t hear every day. To keep it simple, lumens is a metric for brightness. Think of it as meters or feet. We use lumens as a yardstick for brightness and a way for us to know how bright a light bulb can reach. In science, lumens is often abbreviated as “lm,” which is helpful when solving equations related to lumens. 

Hence, having a brighter light output means getting a lighting product with a higher lumen value. In lumens to watts conversion, the wattage depends on the type of lighting used, which is discussed in the later sections. However, as the Spiderman quote goes, “With great power comes great responsibility.” Indeed, a high-lumen light bulb consumes a lot of power. Thus, expect electricity costs to rise if you’re using lighting products that emit very bright lights.

For more context, if you find 100 kilometers very far, it’s the same understanding with lumens. You can say that 100 lumens won’t be as bright as 1,000 lumens. In the next section, we dig deeper into the formula.

Lumens Formula

Lumens is calculated using the formula below:

Luminous Flux (Φ) or Phi = I × A × K

Where:

  • Φ (Phi) is the symbol used to represent luminous flux or the amount of visible light.
  • I or illuminance represents the value of lux. It is the amount of light that touches a surface.
  • A represents the angle of the light rays
  • K is the efficiency coefficient of light at a certain angle

For example, let’s say that we have a light bulb emitting an illuminance level of 200 lux. The area at which the light illuminates is 3 square meters, and the coefficient is 0.8. The luminous flux or lumen is:

Φ = I × A × K

Φ = 200 × 3m2 × 0.8

Φ = 480 lumens

Once you get the lumens, you can use this value for the lumens to watts conversion.

Define Watts

Now that we’re done covering lumens. It’s time for us to discuss watts to fully understand how to convert lumens to watts. To keep it simple, a watt is a unit of power. It is how we measure electric consumption or energy transfer. In the context of LED lighting products, watts are important. Light sources (e.g., LCDs, LEDs, incandescent, fluorescent) use electricity to work. LEDs, in particular, work because of electricity. When electric currents pass through the diodes, the LED chip emits light.

Watts measures how energy is used per second. A watt is equivalent to one joule per second. LED light bulbs and other consumer technology products always specify the number of watts. Sometimes, people misconstrue watts as the main way of determining brightness. For instance, if you want a bright light bulb, you may want to target 15 to 20 Watts. However, that’s not the proper use of wattage in lighting.

When applying the concept of wattage in lighting, your aim is to determine how much electricity a light bulb would consume over a period of time. This measurement is called Watthours. The longer you turn on the light, the more electricity you consume. Hence, LEDs come at an advantage because they have energy-efficient capabilities that won’t hurt the pocket.

Watts Formula in Relation to LEDs

In computing wattage, we use the formula below:

kWH = (Watts x Hours) / 1,000

We won’t go over the scientific computation of wattage because it’s not relevant in the lumens to watts conversion. In the real world, the wattage is always given in the product descriptions and you don’t need to compute it. But if you’re interested in computing watts, check this website that shows you how to compute watts.

Let’s say you have a 10-watt LED bulb at your home that’s on for 12 hours a day. The total kilowatt hours for this consumption is:

kWH = (10 Watts × 12 hours) / 1,000

kWH = 120 Watts / 1,000

kWH = 0.12 kWH

Why do we divide it by 1,000? Since the unit is kilowatt hour, the prefix kilo is actually 1,000. Hence, we need to convert it to make it kWH. This computation is important in lumens to watts conversion.

Now, let’s assume that the price per kWh is $10. How much is the electricity cost of a 10-watt LED bulb that’s on for 12 hours? Simply multiply the price per kilowatt hour with the total kilowatt hours. Hence, the total cost per day is only $1.2. On a monthly basis, that’s $36 of the electricity bill. 

But that’s just for one bulb. If you have 20 LED bulbs running in the same conditions, the daily electricity cost is $24, and the monthly cost is $720. Therefore, even if the wattage is only 10 watts, electric costs can still rise if you have several lights turned on.

Lumens to Watts Conversion Chart

A chart showing the lumens to watts conversion and vice versa.
Conversion Table of Lumens to Watts in Comparison With Different Lighting Sources (Source: The Lightbulb Company)

The image above shows the lumens to watts conversion chart used by different lighting products and their lumen output. Did you notice why LEDs are powerful? Take note of the 18-watt LED bulb. Based on the chart above, an 18-watt LED bulb can generate a lot of lumens while maintaining a low wattage level. Now, let’s compare that to an 18-watt halogen. Both are at 18 watts, but look at the lumen output. An 18-watt halogen only emits more than 220 lumens versus the more than 1,300 lumens for LEDs.

Now, that’s the reason why LEDs use less electricity. For a standard bulb, the lowest wattage is 25 watts, and it generates more than 220 lumens only, while for an LED bulb, it’s only four watts. Therefore, knowing your way around wattage and lumens can help you save electricity and get the desired lumen output.

Convert Lumens to Watts & Vice Versa

In converting lumens to watts and vice versa, we use the following multipliers:

  • LEDs: Multiply wattage by 80
  • Incandescent: Multiply wattage by 15
  • Halogen: Multiply wattage by 20
  • CFL: Multiply wattage by 70

The multipliers above compute the lumens per watt. Hence, we can say that one watt is equivalent to 80 lumens for LEDs, 15 lumens for incandescent, 20 lumens for halogens, and 70 lumens for CFL.

For example, how much lumen output can a 20-watt LED bulb generate? We simply multiply 20 watts by 80, and the lumen output is 1,600 lumens. This level of lumen output is so bright for a small area. Hence, try a lower wattage instead.

Now, for comparison, let’s say we have a similar incandescent bulb at 20 watts. How many lumens can it generate? Let’s compute. Multiply 20 watts by 15, and the lumen out is only 300 lumens. That’s a bit low compared to LEDs that can reach 1,600 lumens.

To give more perspective, let’s say we turn on both bulbs for 12 hours a day with an electricity cost of $10 per kWH. However, since the incandescent bulb only generates 300 lumens, let’s make it five bulbs so that it generates a lumen output of 1,500, which is closer to our 1,600-lumen LED bulb.

Which bulb is cheaper to operate?

LED (1 Bulb Only)Incandescent (5 Bulbs)
(20 watts x 12 hours) / 1,000 x $10
240 / 1,000 x $10
Total Cost per Day = $2.4
Total Cost per Month = $72
(20 watts x 12 hours x 5) / 1,000 x $10
1,200 / 1,000 x $10
Total Cost per Day = $12
Total Cost per Month = $360

It’s very obvious why LEDs are cheaper to operate. For 1,600 lumens, you only need one 20-watt LED bulb. But for incandescent bulbs, you need at least five to reach close to 1,600 lumens.

Now, let’s try to compute watts to lumens. To do this, let’s just reverse the process above:

  • LEDs: Divide lumens by 80
  • Incandescent: Divide lumens by 15
  • Halogen: Divide lumens by 20
  • CFL: Divide lumens by 70

If we have a light bulb emitting 600 lumens, how many watts does it use if it’s (1) an LED bulb and (2) an incandescent bulb?

LEDIncandescent
600 lumens / 80 = 7.5 watts600 lumens / 15 = 40 watts

Clearly, we can see that LED bulbs are indeed cost-efficient at 7.5 watts only while an incandescent bulb reaches 40 watts.

Best Use of Lumens and Watts

In the discussion above, we have ascertained that lumens and watts have their proper uses. Therefore, understanding the best use of each will help us further make use of its unique attributes and uses. Below, we’ll discuss further the best use case of lumens and watts to help you decide which term is more appropriate for a certain situation.

Lumens: Best for Measuring Brightness

By now, you should have understood that lumen is the better term to use when we want to describe brightness. Lumens impact how bright the light is in a given area. Brighter doesn’t mean better. You should always acquaint the light with the size of the area. In understanding lumens to watts equivalent, you should always remember that more lumen output means more wattage consumption.

But how important can lumens be? Let’s find out in the following bullet points:

  • A lumen is our yardstick for measuring brightness, like a meter stick to measure distance and height.
  • A higher lumen output will always generate more light, but its illuminance might depend on the area.
  • Even if the lumen output is high, the size of the area heavily dictates how much area the light can illuminate.
  • Knowing the size of the area is key to knowing which lumen level is ideal.
  • Too much light can cause light pollution. Hence, picking the ideal lumen output is required.
  • Too little light might cause accidents or lead to poor eyesight.
  • Higher lumens mean higher wattage. Using more electricity has an environmental impact, so choosing your lighting products well is important if you’re a conservative person when it comes to environmental causes.

Watts: Best for Calculating Power Consumption

Wattage is how we determine how much electricity a lighting product has used over time. To understand wattage, you need to remember two elements: watts and hours. The longer we use lighting products, the more electricity it uses. Hence, choosing energy-saving products like LED bulbs and displays can help you generate more light output at a fraction of the cost.

Now, let’s discuss wattage importance in the bullet points below:

  • Higher kilowatt hours in lighting products means higher electricity costs.
  • Choosing energy-saving lighting products like LED can help you reduce electricity costs. However, it still depends on the number of hours used.
  • A lower wattage will help you save more electricity. Refer back to the lumens to watts chart and see what the best lumen output is for your needs. Find the corresponding LED wattage. 
  • To save electricity, it’s best to have the optimal lumen for your needs. For example, a small room won’t need a light bulb with 1,000 lumens or more. Hence, try getting somewhere around 400 to 700 lumens.
  • If you use a lot of electric appliances and lighting, try to take conservative measures by turning off lights when they are not used.
  • Investing in LED lights is one way of reducing the electricity cost of lighting. LED screens and displays also contribute to less wattage.

The Case of LEDs

Indeed, we’ve seen that LEDs generate more lumens at a lower wattage output. Regardless of whether it’s a lighting product or display, LEDs always give the best lumen output at a fraction of the wattage if compared with other lighting products. LEDs generate light when electricity interacts with passing electric current. It doesn’t generate heat when emitting light because it doesn’t need burning elements to produce light. Hence, LEDs don’t create a lot of heat as well.

Since LEDs are characterized this way, it’s normal if they are priced higher than other lighting products. For instance, LED panels are typically more expensive than LCD panels. It is also the same case for fluorescent bulbs, that are priced more affordably than LEDs. Hence, LEDs require quite an investment, but you get lesser electricity consumption and lower electricity bills in the long run.

Another great feature of LEDs is that they can last longer than traditional displays or lighting. Even if LEDs can generate 2,000 lumens, you can still expect them to last from 10 to 15 years, depending on the brand and quality of the product. Therefore, LEDs are worth the investment, given that they generate higher lumens, consume lower wattage, and last for years. 

Conclusion

Understanding the relationship between lumen and watts is crucial in making design and functional decisions at home. Knowing how much electricity a lighting product uses enables you to choose which lumen value is best for a given area. With the help of the lumens to watts conversion chart, you can see why LEDs are energy savers compared to CFLs and halogens.

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