How to choose the wattage of an LED bulb?

Understanding units of measurement: Watts vs Lumens

The Lumen revolution

The first step to choosing the right wattage for your LED bulb is to understand the fundamental difference between watts and lumens. Watts measure a bulb's power consumption, while lumens measure the amount of light actually produced. With the old incandescent bulbs, these two values were proportional, making the choice simple: more watts meant more light.LEDs have changed this equation. A 10-watt LED bulb can produce as much light as a 60-watt incandescent bulb, while consuming six times less energy. That's why it's now essential to focus on lumens when assessing the real light output of an LED bulb. On average, an LED bulb produces between 80 and 120 lumens per watt, while an incandescent bulb produces only 10 to 17 lumens per watt.

Practical correspondence table

To help you make the mental transition from old bulbs to LEDs, here is a cross-reference table:

• Incandescent bulb 25W = LED 3-4W = approx. 250 lumens
• Incandescent bulb 40W = LED 5-6W = approx. 470 lumens
• 60W incandescent bulb = 8-10W LED = approx. 800 lumens
• Incandescent bulb 75W = LED 10-13W = approx. 1100 lumens
• Incandescent bulb 100W = LED 13-16W = approx. 1600 lumens

These matches give you a solid basis for replacing your old bulbs with LEDs without losing brightness. However, for optimum lighting, it's important to consider other factors, which we'll look at later in this article.

Calculate your lighting needs by room

The concept of recommended luminous flux

Every room in your home has specific lighting requirements, depending on its function, size and wall color. To determine the power required, professionals use a unit called the lux, which corresponds to the number of lumens per square metre. This approach allows you to calculate your exact requirements by multiplying the surface area of your room by the recommended number of lux.Lighting standards vary according to the use of each space. A living room generally requires between 100 and 150 lux to create a warm, comfortable atmosphere. A kitchen, where you need to see clearly to prepare your meals, requires 300 to 500 lux. Offices and workspaces require 400 to 500 lux to avoid eyestrain, while a bathroom needs 200 to 300 lux, with more intense lighting near the mirror.

Practical calculation for each space

For a 20 m² living room, aiming for 150 lux, you'll need a total of 3000 lumens. If you're using a central ceiling light, choose a 3000 lumen bulb or fixture. If you prefer to distribute the lighting with several sources, divide this total: for example, three lamps of 1000 lumens each or five lamps of 600 lumens.For a 15 m² kitchen requiring 400 lux, the calculation gives 6000 lumens. However, it is often preferable to combine general ceiling lighting with directional spotlights above worktops. You could install a 3000 lumen ceiling light for ambient lighting, and add 500 to 800 lumen LED spotlights above preparation areas.A 12 m² bedroom requires around 1200 to 1800 lumens for comfortable general lighting. Nevertheless, you should opt for several adjustable light sources: a 1000 lumen ceiling lamp for general lighting, complemented by bedside lamps of 300 to 400 lumens each for reading.

Different types of lighting and their specific requirements

General or ambient lighting

General lighting is the main source of light in a room. It must be powerful enough to allow you to move around safely and perform daily activities without visual effort. For a standard living room of 20 to 25 m², general lighting of 2500 to 3500 lumens is recommended. You can opt for a central ceiling light with a powerful LED bulb, or several recessed spotlights that distribute the light evenly.In open-plan spaces such as American kitchens, general lighting needs to be more important because of the surface area covered and the varied activities that take place there. Choose modular solutions with dimmers, so you can adapt the brightness to the time of day and the mood you want.

Functional or accent lighting

Functional lighting meets specific needs in areas where you perform tasks requiring good visibility. In a kitchen, the spotlights under the wall units illuminating the worktop should provide 500 to 800 lumens per linear metre. For an office or reading area, a desk lamp should produce between 400 and 800 lumens, depending on whether you're working on a computer or reading paper documents.In the bathroom, lighting around the mirror is crucial for daily care and make-up. Plan for 800 to 1200 lumens distributed on either side of the mirror to avoid unsightly shadows. Wall lamps with LED bulbs of 400 to 600 lumens each are an ideal solution.

Accent and decorative lighting

Accent lighting highlights architectural elements, works of art or creates a special atmosphere. For these applications, light output can be more moderate, typically between 200 and 500 lumens per source. LED strip lights, very popular for indirect lighting, offer remarkable flexibility, with adjustable wattages depending on the length installed.Adjustable spotlights to highlight a painting or shelf require between 300 and 500 lumens. What's important here is not so much power as beam direction and color temperature, which must be chosen according to the object or area to be highlighted.

Factors influencing the choice of wattage

Ceiling height

The height of your ceiling has a direct influence on the power required for effective lighting. The higher the ceiling, the further the light has to travel before reaching your living spaces, and the more it diffuses into the space. For a standard height of 2.40 to 2.70 meters, the usual recommendations apply. However, for ceilings of 3 metres or more, the light output needs to be increased by 20 to 30%.In a room with a cathedral ceiling or mezzanine, lighting becomes a real challenge. Choose more powerful light sources, with LED bulbs of 1500 to 2000 lumens or more, or multiply the light points. Height-adjustable suspension fixtures can be an elegant solution, bringing the light source closer to activity areas.

Room colors and materials

The ability of surrounding surfaces to reflect light plays a major role in the efficiency of your lighting. A room with white or light-colored walls reflects up to 80% of the light, making the space naturally brighter. Conversely, dark or brightly colored walls absorb a large proportion of the light, requiring 30-50% more light output to achieve the same effect.Shiny materials such as tiles, mirrors or lacquered surfaces increase light reflection and can create glare if the lighting is too intense. In these areas, use bulbs with diffusers and consider dimmers to adjust intensity. Wooden fabrics, carpets and furniture absorb more light and require more generous lighting.

Available natural light

The exposure of your rooms to natural light has a major influence on your need for artificial lighting. A south-facing room with large windows will need less artificial lighting during the day than a north-facing room with small openings. However, it is important to provide sufficient lighting for periods when natural light is lacking.In rooms with good natural light, you can opt for slightly less powerful LED bulbs for general lighting, compensating with targeted accent lighting for work areas. Brightness sensors and automatic dimmers offer a modern, cost-effective solution, adjusting light intensity according to available daylight.

Color temperature and its impact

Understanding Kelvins

Beyond light output, color temperature, measured in Kelvins, has a considerable influence on the atmosphere of a room and your perception of brightness. A warm 2700K to 3000K light, tending towards yellow-orange, creates a cosy, relaxing ambience, ideal for relaxation areas. A neutral light from 4000K to 4500K, close to daylight, is ideal for work areas and kitchens. A cool light of 5500K to 6500K, tending towards blue, stimulates concentration and is ideal for garages or workshops.Paradoxically, cold light can appear more intense than warm light of the same lumen output, because our eyes are more sensitive to blue tones. For a bedroom where you're looking for relaxation, an 800 lumen warm white bulb will be more pleasant than a cold white bulb of the same wattage, which might seem too stimulating.

Adapt the temperature to each room

In a living room, choose temperatures from 2700K to 3000K to create a warm atmosphere conducive to conviviality and relaxation. This warm light enhances the wood tones and creates a welcoming ambience. You can, however, use a more neutral 4000K light for an office area integrated into the living room.Kitchens and bathrooms benefit from more neutral 4000K lighting, offering good color rendition and sufficient clarity for precise tasks. In the bathroom, lighting from 4000K to 4500K around the mirror lets you apply make-up or shave with true color vision.Offices and workspaces benefit from being lit with temperatures from 4000K to 5000K, promoting concentration and reducing eyestrain. Some modern LED bulbs even offer adjustable color temperatures, allowing you to switch from a warm light in the morning to a cooler, more stimulating light in the afternoon.

Diffusion angle and its importance

Spotlights and directional lighting

The beam angle, measured in degrees, determines the area illuminated by your LED bulb. A spotlight with a narrow angle of 25 to 40 degrees focuses light on a precise area, creating an intense beam of light. These spotlights are ideal for accent lighting, highlighting a painting, sculpture or architectural feature. To achieve the same result as diffused lighting, you'll need to choose bulbs with higher wattages.An average angle of 60 to 80 degrees is suitable for functional lighting, such as kitchen spotlights above a work surface or a desk lamp. The light is sufficiently concentrated to effectively illuminate the work area, while offering a certain diffusion. For a kitchen worktop, 500 to 700 lumen spotlights with a 60-degree angle spaced every 60 to 80 cm provide optimum lighting.

Diffused and ambient lighting

For general room lighting, choose bulbs with wide beam angles from 100 to 360 degrees. These bulbs distribute light evenly throughout the room, avoiding shadows. LED globe bulbs with 360-degree diffusion are particularly effective in ceiling or suspended fixtures, where light needs to spread in all directions.LED strip lights generally offer a 120-degree angle, ideal for indirect lighting behind cornices or under furniture. To calculate the number of lumens required with directional lighting, allow for around 30% more power than with diffused lighting, as some of the light is lost outside the useful area.

Color rendering index (CRI)

What is IRC and why is it important?

The color rendering index, or CRI, measures a light source's ability to faithfully reproduce colors in relation to natural light. This index ranges from 0 to 100, with natural light having a CRI of 100. For optimum visual comfort and realistic color perception, choose LED bulbs with a CRI of at least 80.A high CRI is particularly crucial in certain rooms. In the kitchen, a CRI of over 85 enables you to correctly judge the freshness and doneness of your food. In a dressing room or bedroom, a good CRI ensures that the colors of your clothes appear faithfully. For artists, photographers or any activity requiring precise color perception, look for LEDs with CRI above 90, or even 95.

Variable, connected LED bulbs

Modulate power to suit your needs

Variable LED bulbs offer remarkable flexibility, allowing you to adjust light intensity according to the time of day and your activities. A dimmer allows you to reduce light output from 100% to around 10%, transforming a 1000 lumen light into a subdued 100 lumen mood light. This feature is particularly useful in bedrooms and living rooms.Please note, however, that not all LEDs are dimmable. Check that your bulbs are compatible with a dimmer before you buy. Non-dimmable LEDs may malfunction, flicker or have a reduced lifespan if connected to a dimmer. What's more, the minimum power of the dimmer must be compatible with the low power consumption of the LEDs, generally less than 50W in total.

Connected LEDs and their advantages

Connected LED bulbs represent the future of home lighting. They allow you not only to adjust light intensity, but often also color temperature, creating customized lighting scenarios. You can program a maximum intensity of 1000 lumens of cool white light in the morning to wake you up, 800 lumens of neutral light during the day, and 300 lumens of warm subdued light in the evening.These bulbs can be integrated into home automation systems and controlled remotely via smartphone. Some models even adapt automatically to ambient light or follow your circadian rhythm. Although their initial cost is higher, they offer unrivalled flexibility and can replace several types of traditional bulb.

Energy savings and long life

Return on investment for LEDs

LED bulbs are more expensive to buy than traditional bulbs, but their cost-effectiveness becomes clear over the long term. A 10W LED producing 800 lumens consumes 6 times less than an equivalent incandescent bulb and 2 times less than a compact fluorescent. For 3 hours' use a day, an LED will save you around 15 to 20 euros a year per bulb on your electricity bill.Another major advantage is the exceptional lifespan of LEDs. While an incandescent bulb lasts around 1,000 hours and a compact fluorescent 8,000 hours, a quality LED operates between 15,000 and 50,000 hours. At 3 hours a day, this represents 15 to 45 years of service. You'll replace your bulbs 10 to 50 times less often, reducing not only your costs but also your waste.

Choose wisely to optimize service life

Manufacturing quality has a direct influence on the life and performance of your LEDs. Choose recognized brands and check the warranty offered, generally 2 to 5 years for quality LEDs. A premium LED may cost a few euros more, but will last significantly longer than an entry-level model.Thermal management is crucial to LED longevity. Avoid installing high-power LEDs in enclosed fixtures without adequate ventilation, as heat considerably reduces their lifespan. For these applications, choose LEDs specifically designed for confined spaces or models with better heat dissipation.

Common mistakes to avoid

Underestimating light requirements

The most common mistake is to choose LED bulbs of insufficient wattage, often for reasons of economy or confusion with older references. Lighting that's too dim is hard on the eyes and makes spaces look uninviting. Don't hesitate to opt for a wattage slightly higher than the minimum recommendations, even if it means using a dimmer to adjust the intensity to your needs.In large spaces, a single powerful light source often creates unsightly shadows. It's best to distribute several medium-wattage sources to ensure even, comfortable lighting. For a 25 m² living room, rather than a single 3000 lumen ceiling light, consider a combination of a 1500 lumen ceiling light and additional floor or wall lamps.

Neglecting color temperature consistency

Mixing different color temperatures in the same room creates an unpleasant, unharmonious atmosphere. If you're using several light points, make sure they all have the same color temperature, to within 500K. This coherence is particularly important in open spaces where several zones exist side by side.Likewise, beware of temperature differences between adjacent rooms that can be seen at the same time. A hallway in 2700K warm white and a living room in 4000K neutral white will create an abrupt and uncomfortable transition. Ensure a harmonious temperature progression in your home.

Forget about the scalability of your needs

Your lighting needs can change over time, as you change the layout, add dark furniture or change the function of a room. Choose flexible solutions such as luminaires that accept different wattages of bulbs, and variable or connected systems. This flexibility means you won't have to change your entire system for future upgrades.

Practical advice for the right choice

Drawing up a lighting plan

Before you buy your LED bulbs, take the time to create a complete lighting plan for each room. Identify the different zones and their functions, then calculate the lumen requirements for each. Note the types of existing luminaires and their characteristics (bases, accepted shapes, compatibility with dimmers). This preparatory work will help you avoid inappropriate purchases and frustrating returns.If possible, visit a lighting showroom where you can see and compare different wattages and color temperatures in real-life conditions. Online images and descriptions don't always do justice to luminous nuances, and nothing beats direct experience to make the right choice.

Test before you generalize

When replacing the lighting in a room, start by buying one or two bulbs to test them out before fitting the whole house. Live with this lighting for a few days, at different times of the day, to assess whether the wattage and color temperature are right for you. This progressive approach allows you to adjust your choices without excessive investment.Keep your invoices and packaging during the withdrawal or warranty period. If the lighting doesn't suit you, you can exchange your bulbs for more suitable models. Specialized lighting retailers are generally more flexible on trade-throughs than supermarkets.

Focus on quality and certification

Look for quality certifications such as the Energy Star label, CE standards or A+ and A++ energy certifications. These labels guarantee that the advertised performance is real and that the bulb has undergone rigorous testing. Beware of very cheap LEDs that promise exceptional performance, as they often disappoint in terms of color rendering, lifespan and light stability.Consult user reviews before you buy, especially for lesser-known brands. Feedback will inform you about actual durability, consistency of advertised color temperature, and possible problems such as hum or flicker.

Case studies: examples of complete layouts

Lighting for a 25 m² living room

For a 25 m² living room with light walls and standard ceiling height, aim for a total of 3000 to 3750 lumens. Opt for stratified lighting combining several sources. A central ceiling light with a 1500 lumen LED bulb in 2700K warm white provides general illumination. Add two corner floor lamps with 800-lumen bulbs each for mood lighting and reading.To highlight your bookshelf or TV set, install a 500 lumen LED strip for indirect lighting. If you have an office area in the living room, add a 600-lumen desk lamp in neutral white 4000K with adjustable gooseneck. Together, they create a comfortable, modular lighting system, with a total of 4200 lumens that can be adjusted to suit your activities.

Lighting for a 12 m² kitchen

A 12 m² kitchen requires between 4800 and 6000 lumens for optimal lighting. Divide this power between general and functional lighting. Install a ceiling light or recessed ceiling spotlights for 2500 to 3000 lumens in 4000K neutral white, ensuring sufficient brightness for traffic and general tasks.Add LED strips under the wall units, with a total of 2000 to 2500 lumens distributed along the work surfaces. This targeted lighting eliminates cast shadows and provides perfect visibility for food preparation. If you have a central island, decorative pendant lights with bulbs of 500 to 800 lumens each harmoniously complement the lighting while creating an aesthetic focal point.

Lighting for a 15 m² bedroom

For a 15 m² bedroom, opt for modulation and softness. A central ceiling light with a variable LED bulb from 1200 to 1500 lumens in 2700K warm white provides the general lighting needed for storage and dressing. Use a dimmer switch to reduce the intensity in the evening, creating a relaxing atmosphere conducive to sleep.Bedside lamps provide functional lighting for reading. Choose bulbs with 400 to 500 lumens each, also in 2700K warm white. If your bedroom includes a walk-in closet, add 800 to 1000 lumens of dedicated lighting in 4000K neutral white to distinguish clothing colors correctly. Dimmable LED lighting at the head of the bed can replace traditional bedside lamps.

Conclusion

Choosing the wattage of an LED bulb is no longer a simple matter of converting watts. It's a well-considered decision, taking into account the lumens required, the desired color temperature, the right beam angle and the specific features of each room. By mastering these concepts and applying the recommendations in this guide, you can create optimal lighting that enhances visual comfort, adds value to your living spaces and significantly reduces energy consumption.LEDs are a smart investment for your home. Their exceptional energy efficiency, remarkable longevity and growing flexibility with connected models make them the lighting solution of the present and future. Take the time to plan your lighting scheme carefully, don't hesitate to test out different options, and always prioritize quality over price when purchasing.Good lighting transforms the atmosphere of a room and has a direct impact on your daily well-being. By choosing the right wattage for your LED bulbs, you're investing in your comfort, visual health and the enhancement of your home. Whether you're planning a complete renovation or simply replacing a few bulbs, the principles set out in this guide will help you make informed, sustainable choices.