Propagation Grow Lights

Types of seedling or propagation grow lights

If you’ve shopped for grow lights recently, you have likely noticed that there are a lot of different types of propagation grow lights for seedlings and clones. There are traditional technologies such as CFL seedling lights, fluorescent tube grow lights, metal halide propagation lights and now LED grow lights for young plants and seedlings.

Fluorescent tube propagation and Compact fluorescent grow lights have been in use for years as an available technology that produced a cool white (high percentage blue in the spectrum output) in relatively low wattage bulbs. For many years, fluorescent shop lights were the go-to seed starting bulbs for gardeners, but LEDs have quickly replaced them as the standard choice as Fluorescents are very low efficiency compared to modern LED propagation lights.

Metal Halide bulbs have also been used for growing seedlings and young plants as they have a high percentage of blue in the spectrum but are also inefficient and being phased out of production due to inefficiency and being bad for the environment.

LED propagation grow lights are usually more expensive than fluorescent bulbs, but they are very energy-efficient and long-lasting. They also do not produce excess heat and have become available in a wide variety of shapes and sizes. LED seedling grow lights can also be dimmable allowing more precise control of the light intensity the young delicate seedlings require. 

Seedling or propagation grow light spectrum

Plants use light in the photosynthetically active radiation spectrum, which includes wavelengths ranging from 400 (violet) to 700 (red) nanometers. 

The best spectrum output for seedlings and clones has a high percentage of blue in the spectrum or is a cool white. A high percentage of blue in the spectrum promotes short and dense growth in seedlings or clones which is what indoor growers want most. 

A good quality light output with a high CRI (Color Rendering Index) is also desirable because this means the grower can see the colour of the plants clearly and can assess the plant health identifying pests, disease or nutrient deficiencies quickly.

The best light intensity for seedlings or clones

Seedlings, clones and very young plants do not require high light or PAR intensity. Seedlings do not have extensive root development and can dry out under high intensity light and die. It is also critical to have even light distribution so that all of the young plants are getting about the same light intensity and there are no hot spots.

Having dimming control is also very useful so that the grower can adjust the PAR intensity delivered to the seedlings and young plants through the early stages of propagation until they are ready to plant on in larger pots in the veg or flowering grow tent.

We recommend a PAR intensity of 250 µmols/m²/sec for germinated plants or new clones and increasing the PAR intensity up to 400 µmols/m²/sec at three weeks old when they are ready to move to larger pots in the vegging grow area.

Hanging height for seedling grow lights

The hanging height for seedling lights is relatively high as young seedlings or clones require a low intensity and uniform light distribution.

The grow light manufacture should provide a PAR map showing the PAR intensity across the specified growing area at the recommended hanging height so the grower can setup the grow light correctly.

Should I put germinating seeds under light?

Yes, and you need to. As soon as the seedlings have pushed out their cotyledon (baby) leaf pair they are ready for photosynthesis to begin. Switching your light on allows the process to start.

How many hours should the grow light be on for seedlings?

Many growers have a personal preference for e.g. a grow cycle with 18 hours of daily light. Others may prefer 20 hours of daily light of their seedlings.

Can too much light damage seedlings?

Yes, as can excessively strong light from any type of grow light including HPS, CMH or plasma. One of the most common lighting errors, especially from less experienced growers trying to master a new high-power LED grow light is the tendency to damage seedlings with too much light.

How do I know if my seedlings are getting too much light?

Your seedlings won’t grow and will gradually lose vigour the longer they remain under punishingly intense light. The dark green colour turns into paler light green/yellowish tones, sometimes accompanied by tiger prints and curling leaves. Eventually your seedlings will die if left under damagingly strong light.