Best Kelvin Ranges for Indoor Plants

firepowerJuly 14, 2014

I have a number of large tropical plants (banana, coconut, clementine, macadamia nut, etc...) that live indoors in containers through much of the year. I finally went out and bought an indoor growing light with 3 150w metal halide lamps and 8 39w T5 fluorescent lamps. The fixture was originally used for an aquarium setup so it currently has 10,000K lamps installed but I'm thinking that might not be the best for regular plants.

There seems to be a lot of opinions online as to what the best mix is for plants including a fairly good thread here at: and an nice chart from a cannabis perspective at: with a consensus seeming to be around a mix of 6500K and 3000-4000K lamps being best.

Since most of the lamps in my fixture are probably going to need to be replaced anyway, I'm thinking of configuring my light fixture as follows and would like feedback. My goal is to optimize plant growth over the winter months when I need to keep the containers indoors.

1 150w 10000K metal halide lamp
2 150w 6500K metal halide lamp
8 39w 3200K T5 fluorescent lamps

Any thoughts? Is the 10000K lamp in the middle of much value? Is there a better mix?

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Seriously consider whether you need the blue light. Blue stunts stems in species that are phototropic and encourages branching growth. Blue light needs to dominate if you are trying to keep things smaller and bushier. That being said, I am fairly convinced for the general case, the current optimum is to use HPS bulbs with blue spectrum strip lights under lighting the stem. It actually only takes a small amount of bright blue to get the maximum hormonal effect. (One technique for imitating a 24 hour day is to use a bright blue light briefly to divide the dark period in half. A quick blue flash after hours of darkness is all you need for 'day').

Using the T5 full spectrum daylight bulbs will give you ALL the blue you need, even though they need to be close to the plants. They also supply plenty of red, which is part of why they are so popular.

You may want hps conversion bulbs in the 10k fixture.

    Bookmark   August 6, 2014 at 11:46AM
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