Go to content
RED Horticulture
To Understand Light

Kelvin for Horticultural Cultivation

When buying a light bulb, you may have noticed that kelvins appear alongside watts.

14 November 2023

What is Kelvin?

When purchasing light bulbs, you may have noticed that alongside watts, there are Kelvin values. While a common concept in the lighting industry, it is less familiar to many of us.

Kelvin (K) is the absolute unit of temperature measurement. It is called absolute because a temperature of 0 K corresponds to the lowest temperature in the Universe. Unlike degrees Celsius, it is not preceded by the word “degree” and is simply expressed as “Kelvin.” The scale used is the same as that of degrees Celsius but shifted downward by 273.15 units.


Kelvin in Lighting

In the field of lighting, Kelvin is used to characterize the color temperature. Be cautious of shortcuts, as illustrated in the table below: the lower the Kelvin value, the warmer the color. Conversely, the higher the Kelvin value, the cooler the color.

Why? Scientists have chosen to define white light by comparing it to the hue that a black body takes on when heated to different temperatures. The sunlight at noon represents a temperature of 6500K.

Kelvin for Cultivation

The light spectrum varies according to the chosen white temperature. Each plant has specific needs, and it is essential to understand the plant’s requirements to apply an appropriate spectrum.

The graph below illustrates the spectra received for different Kelvin temperatures.

Indeed, by increasing the Kelvin temperature, the blue-to-red ratio in the light spectrum also increases.

"The challenge for me, as a photobiologist at RED, is to choose a white temperature based on production goals. The aim is to vary the proportion of blue and red in the spectra to adapt to the cultivated variety."

Raphaël Quenum

photobiologist, RED

Contact our team of photobiologists now