One of the most common specifications of lights is lumens or lumen efficiency. But, what do lumens mean?

Lumens (lm) are a measure of the total amount of visible light to the human eye from a lighting source. In simple terms, the higher the amount of lumens, the brighter the lighting source is.

This quick guide will explain what are lumens, how this metric works and how to calculate lumens needed.

So, let’s get straight to it!

What are lumens?

Lumens are the international scientific unit for luminous flux. They measure the total quantity of visible light emitted by a lighting source per unit of time. To put it simply, lumens measure the brightness of a lighting source. The higher the amount of lumens, the brighter the light is.

LED lights are often labeled with their light output in lumens and, in many countries, this specification is required by law. The class of energy label is up to lumens. This measure is the international standard for lighting output measurement.

Are lumens and watts the same thing?

Lumens and watts are different measures. Watts are a unit of power that measures electricity, whereas lumens measure brightness. This means that two bulbs with the same wattage can have very different amount of lumens (brightness). 

Watts measures energy use and not lighting output. If your priority is high brightness, focus on the lumen rating. On the other hand, if you want to buy a lamp that will not spend too much electricity, then pay closer attention to the light wattage.

Does higher lumens mean brighter light?

Think of lumens as the “brightness quotient” of a light. The more lumens, the brighter the light. So, if you want a bright light, look for an LED with a high lumen count.

Here’s a simple way to visualize it: One lumen equals the light of one candle. By that measure, a 1000-lumen bulb is like having 1000 candles shining at once—that’s seriously bright!

How many lumens do you need? It depends on the space:

To light up a large, open area, you’ll need a high-lumen solution.

For a cozy, small room, a lower-lumen fixture will provide plenty of light.

 

How do lumens work?

Lumens represent the amount of lighting output that a lamp puts out in any given direction per second. This unit only measures light radiated over visible wavelengths to a human eye from about 400 to 750nm.

Lumens shouldn’t be used as the only unit to determine the amount of brightness needed to cover a certain area. Lumens should always be used together with candelas (cd).

Candelas are a less common unit to measure light intensity. Candela (cd) is the SI-based unit to measure luminous intensity. One regular candle emits approximately 1 candela of luminous intensity, this is why candela used to be called candlepower.

The Difference between Lumens and Candelas

The main difference between a lumen and a candela is that lumens measure the amount of lighting output in any given direction whereas candelas measure the lighting output in a single direction.

Lumens would be the ideal measure for light that needs to cover a large multidirectional area, such as a ceiling light. On the other hand, candelas could be useful for lights that emit brightness in only one direction, such as a spotlight or flashlight.

A light source with 1-candela intensity produces 1 lumen of luminous flux with a 1 square meter surface. This is represented by the mathematical equation 1lm = 1cd * sr.

How to convert lumens to watts?

Lumens and watts are scientific units that represent different quantities, therefore you can’t convert lumens to watts directly.

However, you can use a different formula to calculate watts from lumens and luminous efficacy. This calculation formula is the following:

P(W) = ΦV(lm) / η(lm/W)

The power, which is represented by the letter P in watts (W) is equal to the luminous flux (ΦV) in lumens (lm), divided by the luminous efficacy (η) in lumens per watt (lm/W).

How many lumens do I need?

The number of lumens you need will depend on the room you want to illuminate, its square footage, and your brightness requirements. For example, a large dining room usually requires many more lumens than a small bedroom.

To calculate how many lumens you need, you have to determine your room’s square footage. Then, you will need to multiply your room’s square footage by your room’s brightness requirement.

As a rule of thumb, a bedroom will generally require around 10-20 lumens per square foot, while a bathroom will need a stronger level of lighting, at around 30-40 lumens per square foot. 

A large living space, such as a kitchen or living room will usually require a high number of lumens at around 50-80 lumens per square foot. 

To work out the exact amount of lumens you need, simply multiply the square footage of the room by this figure, which represents your brightness requirement.

For example, if you want to illuminate a bedroom that has 100 square feet, you can multiply 100 by 10 (minimum brightness requirement), for a total of 1000 lumens needed to illuminate the room efficiently.

How many lumens is bright?

A total of 80 lumens per square foot is considered to be very bright. For example, if your room has 100 square feet and your lighting fixtures emit a total of 80,000 lumens, the room will be extremely bright.

For ideal brightness, it is recommended that you pick a light that emits between 50 and 80 lumens per square foot.

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