You can use our lumens to watts calculator to calculate the efficiency of different bulbs and low wattage LEDs based on their brightness to power ratio, known as luminous efficacy, where the brightness of the light is in lumens and its power, in wattage.

You can then compare your LED bulb wattage with other light bulbs to observe how much electricity you'll save. And to further reduce your electricity bill, you may try our outstanding appliance wattage calculator.

Furthermore, we will tell you how to calculate lumens to watts using a formula and show you a comparison chart of LED wattage consumption against other bulbs.

Features of lumens to watts calculator

  • We can use this lumens to watts calculator to find the required LED bulb wattage, i.e., the power needed for our light bulb to produce the specified amount of visible light, based on its luminous efficacy.

  • You can also use it to find the luminous flux, i.e., the brightness of light that our bulb produces with a given amount of power and luminous efficacy.

  • Finally, we can find the luminous efficacy, i.e., how efficiently our light bulb produces visible light based on its power to Lumen ratio.

How to calculate lumens to watts using this calculator

Here's how we use the lumens to wattage calculator for LED lights.

  1. Enter the luminous efficacy of your light source. The default is at 100 lm/W, primarily for LEDs.

🔎 You can find your value from our light bulbs efficiency chart below if you have a different light source.

  1. Enter the brightness of your LED in lumens or nits, e.g., 1200 lumens or 350.25 nits. It is usually mentioned on the packaging of the bulb or you know the lumens of the old bulb you want to replace.

💡 Nit generally measures the brightness of digital displays, such as mobiles, computers, or TVs. For reference, the sun at noon measures about 1.6 billion nits.

  1. Once you have entered your bulbs luminous efficacy and brightness, you'll determine how much power or wattage your light source requires.

    Thus, with a luminous efficacy of 100 lm/W, for producing 1200 lumens, the required power is 12 watts.

Light bulbs efficiency comparison chart

The following table shows a range of luminous efficacies for different light bulbs:

Luminous efficacies of different light bulbs.

Light bulb type

Luminous efficacy (lumens/watt)

LED bulbs

80-120

Compact fluorescent bulbs

45-75

Fluorescent tube lights

40-105

High-pressure Sodium

85-150

Low-pressure sodium

100-190

Sulfur plasma lights

50-100

Metal halide lights

75-100

Mercury vapor lights

35-65

Halogen light bulbs

16-30

Tungsten Incandescent bulbs

12-18

Because different manufacturers have different standards, there are variations in lumens to watts ratio for the same light sources.

You can also try our lighting calculator to determine how much lighting you'll require based on the dimensions of your surface.

How to calculate the wattage of LED lights and other bulbs manually

Based on their brightness and efficiency, we use the following formula when we want to find the required wattage of our low-wattage LED bulbs:

P(W)=ΦV(lm)/η(lm/W)P _{(\text W)} = \varPhi _{V (\text{lm})} / \eta _{(\text{lm/W})}

where:

  • PP – Power required, in watts;
  • ΦV\varPhi _{V} – Luminous flux or the brightness in lumens (lm); and
  • η\eta – Luminous efficacy or the efficiency of producing visible light in lumens per watt (lm/W).

As an example, let's find the required wattage of an LED that has a luminous efficacy of 120 lm/W, and produces 1200 lumens:

  1. Placing the values in the formula, we get:

    P(W)=1200/120=10P _{(\text W)} = 1200 / 120 = 10

  2. Thus, our LED requires 10 watts for producing 1200 lumens.

💡 Standard LED luminous efficacy is between 80 and 120. However, some specific LEDs take this luminous efficacy up to 200 lm/W.

Let's take another example where we wish to find the luminous efficacy of our bulb, which consumes 15 watts and produces 1000 lumens:

  1. In order to find its luminous efficacy, we rearrange the formula as follows:

    η(lm/W)=ΦV(lm)/P(W)\eta _{(\text{lm/W})} = \varPhi _{V (\text{lm})} / P _{(\text W)}

  2. Placing the values in the formula, we get:

    η=1000/15\eta = 1000 / 15

  3. Thus, our bulb's luminous efficacy is 66.67 lm/W.

In case there is no mention of wattage on a device, we multiply its voltage by the electric current in amperes, i.e.,

Wattage = Voltage × Ampere\text{Wattage = Voltage × Ampere}

How to compare wattage of LED to incandescent and other bulbs

Here's an LED wattage chart comparing a low-wattage LED bulb of 12 W at 100 lm/W against other bulb types with different luminous efficacies.

Power consumption of LED vs other light bulbs.

Light bulb type

lm/W

Power consumption

Tungsten Incandescent bulb

15

Requires almost 7 times more power

Halogen light bulb

20

Requires almost 5 times more power

Mercury vapor light

50

Requires almost 2 times more power

Fluorescent tube light

60

Requires almost 1.7 times more power

CFL light bulb

70

Requires almost 1.4 times more power

Sulfur plasma light

75

Requires almost 1.3 times more power

Metal halide light

85

Requires almost 1.2 times more power

The chart tells us that the equivalent wattage of an LED to an incandescent light bulb is almost 7 times less for producing the same amount of light.

Disclaimer: This LED wattage chart only represents approximate values, as different manufacturers have different standards.

FAQ

How do I calculate the wattage of an LED strip?

You can multiply the required voltage by amperes (current) to obtain the wattage.

  • watts = volts × amps

Or you can divide the lumens, i.e., the brightness of the LED strip, by its luminous efficacy to obtain the wattage.

  • η = lm / W

where:

  • η – Luminous efficacy;
  • lm – Brightness in lumens; and
  • W – Power in wattage.

How do I convert 500 watts to lumens?

To convert 500 watts to lumens:

  1. Find the type of bulb to determine its luminous efficacy.
  2. Then multiply the wattage of the bulb with its luminous efficacy to obtain lumens.

For example, if our 500 watts bulb has a luminous efficacy of 40 lm/W: The amount of light it can produce will be 500 × 40 = 20,000 lumens.

Can we use higher wattage LED bulbs?

Yes, as long as your LED wattage doesn't exceed the maximum recommended power load on your fixture or wiring, you can use higher wattage LED bulbs. Be careful not to overload, as that may damage your wiring due to excessively generated heat and cause short-circuiting before catching fire.

How does LED wattage compare to incandescent light bulbs?

The wattage consumption of LED is roughly 7 to 10 times less for producing the same amount of light compared to incandescent light bulbs.

Divide the lumens, i.e., the brightness of a light bulb, by its luminous efficacy to obtain this wattage:

  • watts = lumens / luminous efficacy

Why are bulb lighting colors in Kelvin?

The bulb light colors artificially mimic the Kelvin temperature of a metal object when it’s heated, ranging from 1000 K to 10,000 K.

Lower numbers have warmer tones, while higher numbers have cooler tones.

We generally use between 2700 K to 4100 K lights in our daily lives.

AbdulRafay Moeen
Bulb's efficiency for producing visible light
Luminous efficacy η
lm/W
Bulb's brightness
Lumens
lm
Nits
cd/m²
Power requirements
Power
W
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