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.
How far your lights are from your seedlings depends on the kind of lights that you are using
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: 5-6 inches away from seedlings.
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.
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.