The Meaning of Lumens
One of the most common specifications you will find when browsing for garden lights is the number of lumens. 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 how this metric works and why it is crucial. We will also give examples of the minimum amount of lumens required for different light types.
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 labelled with their light output in lumens and, in many countries, this specification is required by law. This measure is the international standard for lighting output measurement and it is part of the SI system.
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 2 bulbs that have the same amount of watts can have a different amount of lumens (brightness).
Watts measures energy use and not lighting output. If your main goal is to buy a lighting fixture that emits high levels of brightness, you should look at the number of lumens.
On the other hand, if you want to buy a lamp that will not spend too much electricity, then you need to look at the light wattage.
Does higher lumens mean brighter light?
A higher amount of lumens means a brighter light. If your LED light emits a high number of lumens, it will generate a higher lighting output, which means the light will be brighter. On the contrary, if your light has fewer lumens, it is a dimmer light.
As opposed to watts, lumens give you a good indication of how much light you will get in any given direction. As a rule of thumb, 1 lumen equals the brightness of 1 candle.
Therefore, if your light has 1000 lumens, the lighting output will generate brightness equivalent to 1000 candles, which is generally considered to be very bright.
Large spaces require lighting with higher lumens to provide a good level of illumination. However, if you’re looking for a light to illuminate a small room, you can use a fixture with lower lumens.
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) and square radiation, also known as steradian (sr).
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).
Lumens to Watts Conversion Chart
|Lumens||LED Bulb Watts||CFL Bulb Watts||Halogen Bulb Watts|
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 do I need for outdoor lights?
You can use the same formula above to calculate the exact number of lumens that you need to illuminate your outdoor space.
As a rule of thumb, the larger your outdoor space is, the more lumens you will need to light up your garden efficiently.
You can either use fewer lighting fixtures that emit a big amount of lumens, or many lights that emit fewer lumens to cover the same area.
If you’re browsing outdoor security lights, such as LED garden spotlights or solar path lights (see here for the best solar pathway lights in 2023), then it is crucial to opt for lights that emit a large number of lumens. These lights will usually emit between 50 and 80 lumens per square foot.
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.
The brightest solar path lights will usually have a total of 1000 lumens. However, these lights require a larger amount of sunshine, which can be a challenge during winter months.
Generally, it is only recommended to opt for high-lumen solar lights when you're buying a spotlight or security light as these lights need high levels of brightness.