How Far Should My Lights Be From My Seedlings?

Posted by Amy Storey on April 22, 2016

How far should my lights be from my seedlings?

Light intensity is important to moving seedlings through germination to transplant quickly and consistently. How far lights should be from seedlings is one of the most common questions that we get from new and experienced growers alike.



Like most questions, this one doesn’t have one simple answer (sorry), but we have put together a few simple rules for the two most common types of seedling lighting.

Learn more: How long should I leave light on for my seedlings?

How far your lights are from your seedlings depends on the kind of lights that you are using.2015_-_Warehouse-5269.jpg

You’ve got to keep two goals in mind: the amount of light you're giving seedlings, and the coverage of light that you’re giving seedlings.

1) Amount of light:

We can measure the useful light to a plant (PAR - photosynthetically active radiation, or the parts of light that the plant can use to photosynthesize) in micromoles per meter square per second (micromoles/sec-m2) . The goal here is to deliver 120-150 micromoles/sec-m2 of PAR to your seedlings.

Some people will use a PAR meter to figure out how much PAR they’re getting to their seedlings, and will adjust the distance of their lights based on that measurement. Don’t worry- you don’t need one for this if you're using LED bars or fluorescent bars. Just remember the following distances.

LED bars (like Philips): 8-12 inches away from seedlings

T5 fluorescents (like these): 5-6 inches aways from seedlingsLED_vs_Fluorescent1.png

Read more: The Modern Farmer's Guide to Indoor Lighting

2) Coverage of light

The next question is coverage. You can usually just eyeball this to figure out how far apart your lights need to be to deliver the same intensity of light across your entire seedling tray.

Again, we've outlined two simple rules to follow if you're using the most common seedling lighting types:

LED bars: 8-10 inches apart from each other

T5 fluorescents: 4-5 inches apart from each other


Stick to these rules, and your seedlings will be ready to transplant in no time.

In conclusion

Light is one of the most overlooked factors in a plant's growth, but it's also one of the most important. Getting your seedlings enough light will keep your planting and harvesting schedules on track and will help your system stay healthy and robust.

Want to learn more about lighting and indoor ag?

Check out Upstart University, the only online farm training program with redeemable tuition and one-on-one support from industry experts and fellow students.

Enroll Now



Topics: Indoor Growing

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