How to Calculated the Amount of Lighting Need in a Room

A complex subject, the question of lighting is often seen as a specialist’s business, because each room in the house requires very specific lighting. In a kitchen or a bathroom, for example, the need for lighting is much higher than that of the living room or a bedroom and has its own rules and specificities.

The amount of lighting needed for space depends on several parameters: the type of room, the atmosphere you want to create there but also its surface. Lumens, watts or even kelvins, we are often lost among all these units of measurement.

Discover the key elements to finally understand everything, estimate the amount of lighting needed for the room you want to furnish and make you a real lighting specialist!


To illuminate an area of ​​your home effectively while creating a pleasant space for everyday living, you need to learn to master some lighting concepts . Successful lighting emphasizes the areas that we want to enhance and highlight, or the living spaces in which we gather and towards which we want to be naturally directed when entering the room: the dining room table , the living room coffee table , the sofa, the kitchen island , etc.

Another factor, more subjective this one, also comes into account: the style of furnishing of the room. Indeed, with identical lighting, the rendering will be very different between a refined living room with light floors and furnished with white wood, and another more busy living room with imposing furniture and dark ground.

Likewise, the lighting power adapts to activities: work such as homework or preparing meals requires bright lighting, while reading or watching television requires rather diffuse and subdued lighting. This element must therefore be taken into account depending on the areas that one wishes to develop.

Finally, we are very sensitive to the color of the lighting around us and our mood is largely influenced by the color of the light. Cold, direct lighting suggests energy: it is ideal for moments of work. A warm light is it ideal for moments of relaxation: it evokes comfort and calm.


To master your lighting, another essential step is to understand and master the technical data .
3 essential elements appear on the packaging of our light sources and our luminaires:

Watts (W)

This unit measures the electrical power produced by the light source, ie it’s electrical consumption. With the low-consumption bulbs that are the LED and the fluorescent bulbs, this unit of measurement is no longer indicative of the luminous efficiency of a bulb , but of its electrical consumption: the higher the number of watts, the more the bulb consumes electricity  .

Lumens (Lm)

This unit measures the quantity of light emitted by a bulb: it is the luminous flux . This is the decisive criterion as to the brightness produced by a bulb, because for the same consumption expressed in watts, all bulbs do not produce the same amount of light. To understand, imagine the flow of water coming out of your shower head: the further your hand is from the shower head, the less water it receives, or even none at all. Likewise, the further you move your book away from your bedside lamp or reading light, the less light you have to read. Thus, the higher the number of Lumens, the more the bulb produces a significant luminous flux and illuminates efficiently .

Here are some benchmarks on the recommended amount of lumens per living space:

Main lighting for a living room, a dining room, a hallway requires approximately 100 lm / m².

Main lighting for a kitchen or bathroom requires 300 lm / m².

Kelvin degrees (K)

This unit measures the color temperature of light . Paradoxically, the higher the data, the colder the light, in other words “bluish”. And the lower the data, the warmer the light, in other words “orange”. Some benchmarks:

Very warm light: orange in appearance / candle flame, around 1500 K,
Warm light: orange yellow in appearance, around 2700 K,
Soft light: in neutral white appearance, around 4000 K,
Cold light: d bluish appearance, closest to daylight, around 6500 K.

Nowadays we mainly find on the market light sources between 2700 and 3000kelvin : it is the color temperature produced by incandescent bulbs, it is the most neutral and anchored in our uses, neither too hot nor too cold.

The Lux (Lx)

Another data must be taken into account because it is used as a basis for calculating the amount of lighting needed in a room: these are the Lux (Lx). This unit measures the efficiency of the lighting, in other words the flow of light received by an object or a surface: it is the luminous illumination . It is calculated from the lumens emitted by our light sources and the square meters of the surface to be illuminated. To put it simply, a lux corresponds, when the reflection of the support to be lit is good, to 1 lumen per m².


The arrangement and characteristics of the light sources that equip your interior must therefore be designed according to 4 criteria :

  1.   The type of room to be lit,
  2.   The desired atmosphere,
  3.   The appropriate light color temperature,
  4.   The distribution of lighting to take advantage of each space.

Here are some benchmarks to guide you in your choices:

Room and sought-after atmosphere Light intensity Recommended color
Living room, dining room, adult bedroom. Subdued, intimate atmosphere. 25-50 lux White hot
Living room, dining room, kitchen, adult bedroom, office. Friendly atmosphere, moments of relaxation. 100-150 lux White hot
Office, library, children’s room, games room. Atmosphere of work, games. 200-250 lux Neutral white
Technical atmosphere: areas of high activity (office, workshop) and circulation (corridors, entrance) 350-500 lux White cold



Make your life easier with this quick and easy calculation method: lumens / m² = lux!

Let us take the example of the arrangement of a room of 15 m² which one would equip with low consumption bulbs of 9W and which produce 350 lumens.
For a lamp equipped with this bulb and on the basis of the calculation rule cited above, you therefore make the following calculation: 350 lm / 15 m² = 23 lux of illumination.

The amount of Lux produced by a light source must then certainly be multiplied by the number of light points of the same type installed in the room. Thus, with two l bedside lights fitted with this 350 lm bulb, you generate an illumination of 46 Lux and you place yourself in the recommended range for a room with an intimate atmosphere. If you are looking for a less subdued atmosphere in this room, you will simply have to opt for bulbs producing a greater luminous flux, therefore more Lumens, to increase the illumination accordingly.

Let’s take the example of a 25 m² living room equipped with 1000 lm LED bulbs: 1000 lm / 25 m² = 40 lux of illumination.
This obviously cannot be sufficient to illuminate the entire room.

How to calculate the number of light points needed to obtain satisfactory illumination ? Well, by dividing the recommended light intensity in lux with the lux of illumination produced by the light source. This gives you the number of lamps you need to properly illuminate your room!
150 lux recommended / 40 lux produced by your LED bulb = 3.75. This is the number of light points to be installed according to the recommendations in the table. As we need a round number, let’s say 4 in this specific case!

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