K Values for Grow Lights

What value of “K” lighting do your recommend for starting vegetable seeds?  I willbe starting tomato, pepper,and onion seeds in my house for planting in the spring. thank you for your help.



Hi George,

Thank you for the email regarding the K (Kelvin) value needed in grow lights for starting seedlings.

Lower K values indicate warmer (more red) light and higher K values indicate cooler (more blue) light. In nature, sunlight promotes seed germination. The sun provides timing cues and energy for seeds to grow.

In terms of color temperature, sunlight is around 6000 K. By contrast, a standard incandescent bulb has a color temperature of 2700 K. A light that provides a color temperature close to that of the sun will best promote seed germination.

Modern technology has produced a wide variety of light bulbs and each have different properties that make them more or less appropriate for indoor gardening.  Depending on which route you want to go, some I recommend are:

–Fluorescent lights. Full spectrum fluorescent lights provide an efficient source of light with very little heat. To be most effective, fluorescent lights should be placed close to plants. The cool, even lighting provided by
fluorescent lights is perfect for seed germination.  They generally have a K value of 2500-3000.
–Compact fluorescent lights. An upgrade to older technology, CFL bulbs concentrate fluorescent light into a smaller form. CFL bulbs are available in warm and cool color temperatures and make great plant grow lights. They generally have 3500-4000K
–Metal halide lights. With a color temperature of 5500 K, metal halide lights are as close to indoor sunlight as you can get. The hot operating temperature of metal halide lights requires that they be placed at a safe
distance from plants.

I hope this information helps you out.  If you have any other questions, please feel free to ask.


© Mertie Mae Botanics LLC and Horticulture Talk!, 2014. Unauthorized use and/or duplication of this material without express and written permission from this blog’s author and/or owner is strictly prohibited. Excerpts and links may be used, provided that full and clear credit is given to Mertie Mae Botanics LLC and Horticulture Talk! with appropriate and specific direction to the original content.

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