How many LED grow lights do I need for my growing space?

There are 3 important factors to consider in order to determine the number of grow lights you need:

  1. Type of plant(s) you intend to grow
  2. Size of your growing space
  3. The wattage of the LED grow light

Please refer to the charts below to help determine the number of grow lights your space requires:


Wattage Size of grow space in feet (ft)
1000-watt LED grow light 7x7 ft
600-watt LED grow light 6x6 ft
400-watt LED grow light 4x4 ft
250-watt LED grow light 3x3 ft
150-watt LED grow light 2x2 ft



Type of Plant(s) Wattage per square feet (sq. ft)
Vegetables 40 w/sq. ft (4400 lumens)
Rosales 65 w/sq. ft (7150 lumens)
Other 25 w/sq. ft (2750 lumens)


Comparing Different LED Grow Light Styles

Spread style

Most small LEDs belong in this group. They are typically spread over large farming areas. Some great examples include Rack LED grow light, Quantum board, and Spider LED grow lights.

COB Style

They utilize COB (Chip on Board) LED bulbs. Each COB uses multiple LED chips to produce light. Auto COBs are the most common type.

Traditional Panel

These LEDs contain diodes that are small to medium and their lamps are compact. Their features are a mixture of spread and COB styles.

What are some examples of where LED grow lights can be used?

  • Can be used for indoor plants for both domestic and commercial purposes
  • Greenhouses
  • Horticulture
  • Vertical farms
  • Indoor gardens and farms
  • Food production
  • Indoor hydroponics
  • Research laboratories
  • Smart home gardening

 PAR Photosynthetically Active Radiation

Plants perform photosynthesis by absorbing light or photosynthetically active radiation (PAR), which describes the range of solar radiation spectrum that can be used for plant growth from 400nm to 700nm (dark blue to deep red). UV light plays an important role in the formation of natural pigments and defences mechanisms in plants. The most common units used to measure PAR are PPF (Photosynthetic Photon Flux Photosynthetic Photon Flux) and PPFD (Photosynthetic Photon Flux Density)


PPF Photosynthetic Photon Flux

PPF is an important unit for measuring how many photons in the range of PAR are emitted from the light source per second, expressed in μmol/s (micromoles per second). 1 μmol is equal to 602,214,150,000,000,000 photons (6.022 x 1017). But PPF cannot represent how many photons really fall on the plant, it is just the cumulative total photon output of the lamp.


PPFD Photosynthetic Photon Flux Density

PPFD is usually used to indicate the intensity of light, which indicates how many photons per second shine on an area of 1 square meter, with μmol/m2/s as the unit. PPFD is the most important number for growers. It can tell you how many photons hit the plant. PPFD will vary depending on the size of the fixture and the distance from the lamp to the plant. The longer the distance, the lower the intensity density.

It is very basic and necessary to measure and average the PPFD values of multiple growing areas to see if the plant light is effective enough. When you want to compare various plant lights, you need to measure PPFD at multiple points to assist in your decision.


Relative Quantum Efficiency

The PPFD value does not give complete information about the relative intensity of a particular wavelength. High PPF/PPFD numbers for plant growth lights do not mean that plants will grow well. The relative quantum efficiency curve is also called the effective light quantum flux Yield Photon Flux (YPF) curve or McCree curve, and is wifely used to evaluate the effective light quality and light quantity of photosynthesis. The curve shows that orange and red photons between 600-630 nm have 25% more photosynthetic efficiency than blue photons between 400-540 nm. Therefore, when evaluating the effectiveness of light, it is necessary to consider the distribution of the spectrum.


The McCree Curve

 For the efficiency of overall growth, growing leaves during the vegetative stage of the plant ot produce nutrients for the benefit of photosynthesis will prepare a large number of root growth and plant architecture (stem spacing and overall stem strength). The light source provides energy to the plant at this stage to help the plant prepare for future flowering and fruiting.

At this stage, growers can choose many artificial light source technologies to adjust the plant to increase yield. Promoting light in the vegetative stage is as important as promoting light in the flowering and fruiting stages. Because artificial light is the only source of energy that we give to all growth stages of a plant, the quality and type of light you choose is crucial.


Understanding Photosynthetic Active Radiation (PAR)

PAR is the measurement of light output that lies within the wavelength range of 400 to 700 nanometers. One can measure Photosynthetic Active Radiation is by the amount of μmol/m2/s (micromoles/square meter/second). Plants require different PAR outputs on different growth stages. The higher the PAR, the higher amount of edible light your plan receives, allowing for maximum growth.


Growth Stage Required PAR Output
Seedling 200 – 400 (μmol/m2/s)
Veg 400 – 600 (μmol/m2/s)
Flowering 600 – 900 (μmol/m2/s)


What is Photosynthetic Active (PAR) Value and Choosing the Right Value

PAR shows the type of light within the photosynthetic range of 400 nanometers to 700 nanometers. The value of PAR is estimated in photons and the PAR value of natural sunlight is 900 – 1500 μmol/m2/s when it’s directly overhead. To ensure that the LED grow lights used for indoor plants mimic sunlight and produce an adequate light source, their PAR value should be between 500 – 1500 μmol/m2/s. Different professional LED growth lights emit different PAR values for plants based on the different growth stages of plants. Since a typical LED growth light utilizes the full spectrum of light, the PAR levels have to be adjusted and customized to the stage of growth your plants are in. If they are clones, mother plants, or seedlings, a grow light producing 200 – 400 PPFD (photosynthetic photon flux density) is suitable for your plants. However, if your plants are vegetative or in the late growth stage, an LED grow light generating 400 – 600 PPFD is the right fit. Finally, if they are flowering, budding, or fruiting, select a 600 – 900 PPFD LED grow light.

Direct sunlight is ideal for most plants since it provides all colours of the light spectrum. However, the downside is that it also produces harmful rays that damages plants and inhibits proper growth or even cause death of plants. Because of this, growers turn to indoor farming using LED grow lights, which provides the most control as light levels can be adjusted according to plant needs. This is just one of many reasons why LED grow lights are the most advantageous option, providing cost-effective and energy-friendly options to growers.