Beacon Lighting Supply | Lighting the Way

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A Beginner’s Guide to Understanding Lumens, Watts, and Kelvins

Walk down the lighting aisle at any store today, and you’ll see bulbs labeled with numbers that might make your head spin — 800 lumens, 9 watts, 2700K, and more. Gone are the days when you could simply grab a “60-watt bulb” and know exactly what you were getting. Modern lighting has evolved, especially with the rise of LEDs, and so have the ways we measure brightness, energy use, and color.

If you’ve ever wondered what those terms on the box actually mean — lumens, watts, and Kelvins — this guide will make it all clear. Whether you’re designing a cozy living room, illuminating a workspace, or upgrading to energy-efficient lighting, understanding these three key measurements will help you choose the right light every time.

1. Lumens: Measuring Brightness

Lumens (lm) measure how much visible light a bulb produces — in other words, how bright it appears to your eyes.

Think of lumens as “light output.”

For example:

Traditional Bulb	Approx. Lumens	Typical LED Equivalent
40W incandescent	450 lumens	5–6W LED
60W incandescent	800 lumens	8–10W LED
75W incandescent	1,100 lumens	12–14W LED
100W incandescent	1,600 lumens	16–18W LED

Quick tip:

When replacing bulbs, use lumens to compare brightness, not watts. A “60-watt equivalent” LED will usually produce about 800 lumens, even though it uses only about 9 watts of power.

2. Watts: Measuring Energy Use

Watts (W) used to be the go-to way to measure how bright a bulb was — but that’s no longer true. Watts measure power consumption, or how much energy a light source uses.

In the past:

With incandescent bulbs, more watts meant more light — but also more heat and wasted energy. For example, a 100-watt incandescent bulb was brighter than a 60-watt one because it consumed more energy to produce light.

Today:

Thanks to energy-efficient technologies like LEDs (Light Emitting Diodes), we can get the same brightness with far less power.

Example:

All three bulbs produce the same amount of light, but the LED uses about 85% less energy.

That’s why watts no longer measure brightness — they measure how much electricity the bulb draws from the socket.

Why this matters:

3. Kelvins: Measuring Color Temperature

If lumens tell you how bright a light is, and watts tell you how much power it uses, Kelvins (K) tell you what the light looks like.

Kelvin measures color temperature, which affects the mood, function, and appearance of a space. It’s not about heat — it’s about how warm or cool the light appears to your eyes.

The Kelvin scale:

Color Temperature	Appearance	Common Description	Typical Use
2200K–2700K	Warm, yellowish	“Soft White”	Bedrooms, living rooms, and restaurants
3000K–3500K	Warm white / neutral	“Bright White”	Kitchens, bathrooms, retail
4000K–4500K	Cool white	“Neutral White”	Offices, garages, workshops
5000K–6500K	Daylight / bluish white	“Daylight”	Outdoor areas, task lighting, display lighting

How to choose color temperature:

Choosing the right Kelvin temperature can completely change the feel of a room. For example, a warm white (2700K) makes your living room feel like a sunset glow, while daylight (5000K) makes a workshop feel sharp and clear.

4. How Lumens, Watts, and Kelvins Work Together

These three values — lumens, watts, and Kelvins — describe different aspects of the same bulb. Here’s how they fit together:

When choosing a bulb, you’ll want to balance all three based on your needs.

Example 1: A cozy living room lamp

Example 2: A kitchen work area

Example 3: A garage or workspace

By reading the lighting label carefully, you can customize the light for both function and feel.

5. Reading the Lighting Facts Label

Most bulb packaging now includes a Lighting Facts label, similar to a nutrition label on food. It shows:

Take a moment to check that label before you buy — it gives you all the information you need to choose wisely.

6. Bonus: Understanding CRI (Color Rendering Index)

While not one of the “big three,” another term you might see is CRI, or Color Rendering Index.

CRI measures how accurately a light source reveals colors compared to natural sunlight (rated 0–100).

If color accuracy matters — for example, in a kitchen or gallery — look for high-CRI LEDs.

7. Choosing the Right Bulb for Every Space

Here’s a quick cheat sheet for common areas:

Space	Recommended Lumens	Color Temperature (Kelvins)	Notes
Living Room	800–1600 lm	2700K–3000K	Warm and cozy
Bedroom	450–800 lm	2700K	Soothing, helps relaxation
Kitchen	800–1500 lm	3000K–4000K	Bright and clear for cooking
Bathroom	700–1300 lm	3500K–4500K	Clean, flattering light
Home Office	1000–2000 lm	4000K–5000K	Crisp for focus
Garage / Workshop	1500+ lm	5000K–6500K	Daylight for visibility
Outdoor	700–2000 lm	3000K–5000K	Cooler tones for security

8. Putting It All Together

Let’s say you’re upgrading your old bulbs to LEDs. Instead of grabbing “60-watt bulbs,” you’ll now shop with this mindset:

Example:

You want a cozy reading nook:

9. Why It Matters

Understanding these terms isn’t just about picking the right light — it’s about saving energy, money, and creating better environments.

Lighting isn’t just functional anymore — it’s design, sustainability, and psychology all rolled into one.

10. Final Thoughts

Next time you shop for a light bulb, forget the old wattage rule. Instead, think in lumens, watts, and Kelvins — the modern language of light.

By understanding these three simple concepts, you’ll never again stand in the lighting aisle wondering which bulb to buy. You’ll know exactly how to choose the right light for your home, office, or outdoor space— efficiently, beautifully, and confidently.