Best Kelvin Temperature for Indoor Plant Growth in 2026: Best Kelvin Light Spectrum

LED grow lights are becoming very popular and are a good choice if you’re buying a new plant lighting system or upgrading old fluorescent lights. This article about LED grow light myths will save you time and money.

As with any new technology, there are many myths about LED grow lights. Some are created due to public lack of knowledge, but there are also many myths created by manufacturers trying to sell their products. Some of them want to keep us in the dark so they can make outrageous claims, but better companies do not. We need to do our part and become informed consumers so we can properly evaluate both the message being conveyed and the product itself.

What is the Light Spectrum?

The light spectrum can encompass the range of wavelengths of electromagnetic radiation our eyes are sensitive to—the visible spectrum—or a chart of light intensity versus its wavelength. Simply put, it’s the different wavelengths of energy produced by a light source. Nanometers (nm) are the unit of measurement for light, with each nanometer representing a band of light energy or a wavelength of light.

What is PAR?

PAR stands for “Photosynthetically Active Radiation,” a term referring to the spectrum of a grow light covering the light color range from 400nm to 700nm, which can be used by plants for photosynthesis. PAR measurements are often expressed as PPFD—Photosynthetic Photon Flux Density, in µmol m⁻² s⁻¹. It can also be expressed as total Photon Flux (PPF). This expression counts all photons within the PAR band exiting the bulb or lighting fixture. While there are significant caveats, generally, the higher a light’s PPFD value relative to the total growing area, the better the plants will grow. However, using too much PAR is wasteful and can harm plants. This is less of a problem with artificial grow lights.

Fundamentally, PAR light measurements do not account for the relative usefulness of specific wavelengths to plants. Even within the PAR range, some photons are still more useful to plants because leaves preferentially absorb different spectra. Also, high PAR doesn’t automatically mean plants grow well under the light; spectrum must be considered. Furthermore, PAR also assumes that all photons outside the 400nm-700nm range are useless for photosynthesis.

However, plants use some light outside PAR, such as far-red light beyond 700nm, to increase photosynthetic efficiency. Additionally, below 400nm, UV light enhances secondary metabolites like THC, terpenes, vitamins, and CBD. Significant variations in a light’s illumination area can occur in PAR measurements. Therefore, any single PPFD measurement does not provide enough information about how the light will illuminate the plants. Only by measuring PAR across the entire illumination area of the light at an appropriate hanging distance above the plants and observing the entire spectrum can you make meaningful comparisons.

What is Kelvin?

Kelvin is the scale used to denote “color temperature,” an elegant way of expressing the spectrum (color) of light emitted by a particular bulb.

• Growth Stage – 5000K/6500K:
  Bulbs with a bluer hue are called “Cool White” or “Daylight” and are listed with a Kelvin of 5000K/6500K. These “high kelvin” bulbs are optimal for the vegetative growth stage. These CFL bulbs mimic the color temperature of the sun in spring/summer.

• Flowering Stage – 2700K:
  Bulbs with a more yellow/red tone are listed as “Warm White” with a Kelvin of 2700K. These “low kelvin” bulbs are optimal for the flowering stage.

CFGROW 300W COB LED Grow Light

Pros
Decreases operating costs
Year-round production
Suitable coverage

Cons
Indoor use only

See details and prices on amazon here

Relassy 150W Waterproof Plant Light, Full Spectrum LED Grow Lamp

Pros

Easy to set up
Durable
Highly resistant

Cons

Small size
Heating issues
Not suitable for commercial growing purposes

See details and prices on amazon here

SANSI 200W LED Grow Light, Full Spectrum 4000K Daylight Plant Light

Pros

Good for all stages
Suitable for hydroponics
Dim IR/UV but highly efficient

Cons

Small coverage
Not good for commercial use
SANSI Quantum Board can be your great choice.

See details and prices on amazon here

How Far Should LED Grow Lights Be From Plants?

While LED lights don’t generate as much heat as HID lamps, they still emit very high light intensity, which is excellent for yields but can also cause light burn if you’re not careful. To prevent light burn, you need to ensure the grow lights are positioned high enough above the plant canopy.

Distance from LED Grow Lights to Plants:

LED grow lights of different wattages perform best at different distances. Lower wattage lights, such as 250-watt LED grow lights, should be placed 12-24 inches (30-60 cm) from the canopy. Medium wattage lights, like 600-watt or 900-watt LED grow lights, should be placed 12-36 inches (30-90 cm) from the canopy. High wattage lights, such as 1500-watt, 2000-watt, or 3000-watt LED grow lights, should be placed 24-36 inches (60-90 cm) from the canopy. The general rule is to follow the chart below. When in doubt, always place LED lights farther away.

LED Grow Light Distance Chart:

Conclusion

Initially, understanding LED grow light specifications might be challenging—but once you get the hang of it, growing your own vegetables and fruits at home is incredibly rewarding! This product takes a little time to get accustomed to, but it will help you produce fresh, organic farm-quality fruits and vegetables with the highest possible nutritional value.

Overall, LEDs are an effective lighting solution for replacing natural light. The more familiar you become with this technology, the more beautiful your indoor plants will be.

Find more information about available indoor LED grow lights here: Best Quantum Board LED Grow Light Reviews 2026: Mars Hydro TSW2000 vs Spider Farmer SE3000