Grow Light Basics

All green plants require light to perform photosynthesis. During which, special cells convert the energy contained in the light into sugars. In the process, plants give off oxygen.

Plants vary widely on how much light they need to thrive. Low-light houseplants, such as dracaenas, will generally do fine in a north-facing window. Fruiting edibles, such as tomatoes, need much brighter light — more than even a south-facing window can supply, especially in winter.

This is where grow lights come in handy. You can successfully grow all your plants, from seedlings to established plants, all year long.

Warm vs Cool: Understanding Color Spectrum in Grow Lights

When shopping for grow lights, you will notice they are labeled with numbers like 2700K or 4000K. This refers to their relative warmth or coolness on the color spectrum – the higher the number, the cooler the light. Foliage growth is generally best around 6500K, though many plants need a period of warmer light, around 3000K, in order to produce flowers, and thus fruit.

In other words, if your goal is to simply produce seedlings, leafy green vegetables, or root crops, you only need higher spectrum bulbs. If you want to grow flowers, cannabis, or any fruiting plant (cucumbers, tomatoes, peppers, lemons, etc.), you will need lower spectrum bulbs. Some types of bulbs are available in full-spectrum form, simplifying things.

How Long Should I Leave Grow Lights On?

Plants grown indoors require more hours of light than those grown outdoors. 14 to 18 hours of light per day is recommended for most edible species when grown under artificial lighting. Do not be tempted to leave the lights on 24-7, however – at least six hours of darkness each day is essential to plant health.

Mounting Height. What are PPFD targets throughout the cycle and how do you deliver them using the lighting system?

They are designed to be mounted 48” OC (center to center) spacing. So, two lights fit into a 4×8 rack area or over a 4×8 growing table. Typically growers target the following PPFD levels:

Propogation       150-300 umol/m2/s

Vegetation          300-600 umol/m2/s

Flower                600-1000 umol/m2/s (in some cases up to 1500 umol/m2/s)

For the PG1700c, at 18” mounting height at full power, will deliver close to 1000 PPFD. We recommend continuous metering of the light (can be done with Trolmaster Hydro-X system) or at minimum, periodic metering (weekly with handheld quantum meter). Then using automated or manual dimming to vary light output to meet targets. If lights are rack mounted, they are usually in a fixed position and dimming is only way to vary PPFD. If lights are suspended above plants, then height along with dimming can be used to control PPFD levels.