What is Kelvin and why do you need it?

Introduction

White light has two important properties: the amount of light (expressed in lumens or lux - we go into this in more depth in this blog) and the colour temperature.

The term colour temperature, expressed in degrees Kelvin (K), is based on the colour a particular metal or gas gives off when it is heated to a certain temperature. For example, 2400K corresponds to 2,126.85 °C. This scale dates back to the days of incandescent bulbs.

With LED technology, this naturally works differently. Today, white LED strips are made by applying a phosphor coating to a blue LED to make the LED white. The warmer the light (more orange), the thicker the phosphor layer. The colder the light (more blue), the thinner the phosphor layer.

Which colour temperature should I choose?

Let's start with a few familiar reference points:

• Candlelight: around 1800K
• Daylight: around 5600K

The colour temperature of lighting largely determines the atmosphere you want to create:

🔥 2400K - 2700K: Warm atmosphere
Ideal for accent lighting in bars, bedrooms, living rooms and so on. Perfect for a cosy, relaxed atmosphere.

⚖️ 2700K - 3000K: A balance between atmosphere and functionality
Excellent when you need both atmosphere and functional lighting. Think of kitchens, home offices and the like.

💼 4000K - 5600K: Task lighting
For offices, workshops, factories or production areas, it is essential to use light that matches daylight as closely as possible.

Influence on Mood and Productivity

Our brains are tuned to the rhythm of natural sunlight: waking up at sunrise, getting sleepy at sunset. That explains why people often feel more tired in winter: there is less daylight.

In short:

• Warm light has a calming effect
• Cool light has an activating effect

Practical Application

In workplaces, it is best to choose cold light (4000K – 5600K) to increase alertness and productivity.

For multifunctional spaces, we recommend tunable white: LEDs that can switch between different colour temperatures (e.g. 2700K – 6500K). These are best placed above workstations and set to change automatically throughout the day:

• Morning (6000K) – for an energetic start to the day
• Afternoon (4000K) – neutral and functional
• Evening (3000K) – calmer, promotes a good night's sleep

Warm tones on the other hand have a calming effect. That makes them ideal for bedrooms, restaurants and cafés.

CRI Value: Colour Rendering

The CRI value (Color Rendering Index) indicates how well the light renders the true colours of an object:

• Sunlight has a CRI value of 100
• Lower-quality white LEDs often have a CRI value of up to 80
• From CRI 95 upwards, our eyes can barely see the difference

As mentioned earlier, a white LED is made by applying a phosphor layer to a blue LED. Depending on the quality of the phosphor layer, you get different CRI values. The warmer the colour, the harder it is to achieve high CRI values. That is why we usually choose 3000K or more for functional lighting.

Important Recommendations

• Do not use 2400K LED strips as your only light source. They are hard to find and not powerful enough.
• For warm tones below 2400K, you are better off using an RGBW or RGBWCW LED.
• Choose tunable white in offices or meeting rooms.
• Use cool colours (4000K – 5600K) to increase your employees' productivity.