Lumen Calculator – How do calculate the lumens of LED lights?

What is Lumen? Lumens are a measure of the total amount of visible light emitted from lamps or light sources reaching the human eye. The higher the lumen, the brighter the light. On the contrary, low lumen means the light is weak and dim. 

Therefore, you are often advised to choose a light bulb based on the Lumen parameter. Specifically, how to calculate the lumens of LED lights by the needs? The article “Lumen Calculator” will show you all.

What is Lumen Brightness?

What is Lumen Brightness_

The luminous flux (symbol lumen) is a photometric quantity that tells you the radiant power of a beam of light emitted by a point light source. Or easier to understand it is the total amount of light emitted by a light source.

What is Lumen? Lumens = Light Output (shows the amount of light output or luminous flux).

Lumens (symbol lm) is a measure of the total amount of visible light emitted from lamps or light sources reaching the human eye. The higher the lumen, the brighter the light, on the contrary, the lower the lumen, the weak and dim the light.

A useful lumen is a unit that measures the amount of useful light emitted during a 90-degree angle. Useful Lumens are usually lower than total lumens but are more appropriate for spotlights, where the light is concentrated in one direction.

In the past, we used to buy all 50W or 60W bulbs or lighting fixtures thinking they would provide enough light. However, the Watt unit of power only reflects the power consumed by electricity, not the brightness of the LED bulb. Therefore, it is no longer appropriate to use Watts as a measure of bulb brightness.

Example: A 6.5W LED bulb will produce the same amount of light as a 50W Halogen lamp. This energy is 87% less with the same amount of light output. When using LEDs, more energy is converted into light than into heat. As technology advances, more light can be produced using less energy.

Read More: How to Convert Lumen to Watts – Lumen Watt Conversion Calculator

The formula for calculating the luminous flux of an LED

The formula for calculating the luminous flux of an LED

The luminous flux is used to measure the amount of light emitted by a luminaire, it is not measured in a particular direction of light emission and this value is often stated on luminaire products.

From the formula for calculating the illuminance Lux = lumen/m², we have the following formula for calculating the total number of lumens:

Total lumens = Standard illuminance (lux) x Area (m²) of the room.

For example, a light bulb has an illuminance = 150 (Lux), the room area is 14m², from which we have: 

The total amount of Lumen needed for a 14m2 room is = 150 * 14 = 2100 lumens.

Read More: LED Power Supply Guide – How to choose the best?

Formula to calculate the number of LED bulbs

  • Illuminance (lumens/m2 = lux) = (lamp power (W) * luminous flux (lm/w) * several lights used) / area to be illuminated (m2)
  • Number of lights to use: (lighting area * standard illuminance) / (lamp power * luminous flux)

For example, how to calculate the number of LED lights for a bedroom with an area of ​​​​15m2, with an illuminance of 150 Lx.

Then the luminous flux of the LED will = 150 (lx) * 15 (m2) = 2250 Lumens

LED light provides from 100 lumens per watt is

Lighting power: 2250/100 = 22.5W

Assuming you choose an LED with a capacity of 5W, the number of lights to use is 22.5/5 = 4.5 equivalent to 5 LED bulbs.

This is a formula to calculate the number of LEDs based on the ideal condition that all LED light emitted is directed at the lighting location, not absorbed by the surrounding environment.

Lm/W is a useful way to measure the efficiency of a decorative light by measuring the total light output in Lumens divided by the energy usage in Watts.

Common Watts unit estimate table converted to Lumen: 

Unit Watt Unit Lumens
25W Normal lamp: 230 – 270
35W Spotlight: 250 – 280

Spotlight: 200 – 300 Useful Lumens

Normal lamp: 390 – 410

40W Normal lamp: 440 – 460
50W Spotlight: 330 – 400

Spotlight: 350 – 450 Useful Lumens

60W Normal lamp: 800 – 850
75W Normal lamp: 1000 – 1100
100W Normal lamp: 1500 – 1600

Read More: Lux Lumens Conversion – What to pay attention to?

How many lumens of light are needed for a room?

There is no exact answer to this question. As it will depend on many factors like room size and shape, ceiling height, color scheme, type of lights & accessories, task area, and user needs. Below are the tables and estimates:

Lumens Area Area
Kitchen  300-400
Cooker  700-800
Living room  400-500
Corridor  300
Bedroom  300-400
Large bedroom 700-800
Bathroom 500-600
The bathroom 700-800
Reading area  400

Can Watt be used to determining the brightness of a lamp?

The short answer is no, Watt represents the amount of energy consumed by the product, not how much light (Lumen) the lamp provides. 

That is why you should not rely on the amount of Watt consumed, to choosing to buy any lamp. It will only tell you how much energy the lamp uses, not how much light the lamp produces.

What is the difference between Lumen and Watt?

What is the difference between Lumen and Watt_

In the past, people used Watt to compare incandescent light bulbs. While an incandescent light bulb produces light by burning a filament, only about 5% of the electricity is converted into light energy, the rest is heat. So to achieve the desired light output we need more Watt. 

However, now with the explosive development of lighting technology, especially LED lights. They have the same power consumption as an incandescent bulb but provide different light output (lumens). So the number of watts is no longer relevant, but instead, the lumen number indicates what the light output of the bulb is?

Lumen and watt are 2 closely related and closely related units. An easy example is an LED bulb printed on the box with 80lm/w this indicates the light output produced per watt of energy consumed.

Measuring lumens is not a new concept designed for LEDs. It’s a rating metric that has been used for decades as a measurement of how much light a bulb (or anything else) emits. In 2011, the US Federal Trade Commission began requiring manufacturers of compact, fluorescent, and LED light bulbs to use lumens as an indicator of how bright a lamp is. 

On the packaging, the lumen rating is indicated by a number, followed by “lm” (short for lumens). The higher the lumen number, the brighter the bulb will be.

Read More: Recessed Lighting Calculator – How much light is sufficient?

What factors affect the intensity of an object’s illumination?

What factors affect the intensity of an object’s illumination_

A lot of devices need a high lumen output like a super bright flashlight. However, when you want to calculate and determine the appropriate throughput for an object, you need to ensure the following two factors.

  • How much brightness is required at a light source and how much light is needed to illuminate an object in a given space. When you have calculated the exact level of illumination needed by an object, you can choose the right lamp products for home and work.
  • The luminous flux of an object also affects the aesthetics of the living space. Imagine a house choosing a low-lumen lamp, low light will make the house cold. In contrast, in a bedroom, choosing bulbs with a large lumen level will make the room too bright, dazzling, and difficult to fall asleep.

Read More: Power Consumption Calculator Of Any Electrical Equipment


Above is the general information, answer questions related to “Lumen Calculator“. Capturing important information about lumens and what they mean will help you choose the best lamp models for your space. Wish you will calculate correctly and choose the right brightness for your home.

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