Grow Guide

1. Intensity . The more intensity (quantity) of light the better your plants will grow. By increasing wattages you are increasing the intensity or quantity of light available for your plants. As light levels increase environmental concerns must be monitored (heat, CO2, humidity, and nutrient supply).
2. Spectrum . As light intensity increases, light spectrum becomes more important. Natural sunlight is intense and has a broad and balanced spectrum. Indoor plants require the same high intensity and broad but balanced spectrum.
3. Focus. Delivering the light where it is needed is the job of the reflector. Well designed reflectors utilizing quality materials deliver a higher percentage of the available light where it is needed and do this with excellent uniformity. Quality reflectors also have a longer service life.

light intensity in lumens. Lumens represent how intense or bright a light source is to the human eye. For plant growth, intensity should be measured in watts (ie: 600W or 1000W lamp) or watts per square foot. Typically 40-60+ watts per square foot should be used in a garden (See the Lamp Coverage Guide – HERE)

This is the human eye response curve. This chart shows you what part of the light spectrum our eyes are most receptive to. Light meters are measuring the brightness of a light source at 555 nanometers.

The spectral distribution chart is the best illustration of the quality of the light spectrum.

Light spectrum is the many different wavelengths of energy produced by a light source. Light is measured in nanometers (nm). Each nanometer represents a wavelength of light or band of light energy. Visible light is the part of the spectrum from 380nm to 780nm.

The spectral distribution chart is a visual representation of the light spectrum produced by a lamp. It is a graph showing the relative intensities of a light source at each wavelength. These charts can be used to compare the energy levels of various light sources used for plant growth. They are the most practical way to compare the quality of light created by different light sources. The chart shows exactly which wavelengths of light (measured in nanometers) the plants are receiving.

On the left of the chart is the percent of relative energy. The highest energy output of the light source is plotted as 100% Relative Energy. The 100% peak is used to compare the energy levels of all other wavelengths of light produced by that light source.

The bottom of the chart shows all of the wavelengths of visible light energy that the light source produces. For example, if a wavelength is at 50% relative energy, that peak has half the energy when compared to the 100% peak. Scaling each chart to 100% relative energy allows side by side comparison of light sources with different lumen ratings (intensity) or wattages. For example, a 1000W HPS lamp has more overall intensity than a 400W HPS lamp even though their spectral distribution charts are the same.

Furthermore, a 1000W EYE HORTILUX Blue has 80,000 lumens with a well balanced spectrum when compared to a 1000W EYE HORTILUX Metal Halide with 115,000 lumens. (See examples below.)

The Mcree Curve represents the average photosynthetic response of plants to light energy. The Mcree Curve, also known as the Plant Sensitivity Curve, begins at 360nm and extends to 760nm. This curve can be placed over a spectral distribution chart to see how well a light source can affect plant growth.

Photosynthetic Active Radiation (PAR) was derived from the Mcree Curve. It is a TOTAL count of light energy (in photons) between 400nm to 700nm. The PAR measurement is fast becoming a popular metric of the growing power of a light source.

However, the PAR measurement has two fundamental flaws. First, the wavelengths between 380nm to 400nm and 700nm to 880nm are excluded from the PAR measurement. Second, all photons are weighted equally regardless of wavelength.

The Mcree Curve clearly shows plants respond to energy outside the 400nm to 700nm PAR range. Furthermore, plants respond differently to energy within the PAR range.

A PAR meter only measures photons between 400nm and 700nm. As you can see in the example above PAR does not distinguish which photons of light are present, rather it only counts the total amount of photons present in those nanometers.

While the human eye might not notice any difference in light intensity or subtle shifts in spectrum over as few as six months, our research demonstrates that your plant will. Burning lamps for 12 or more hours every day diminishes both intensity and spectrum. This happens with all lamp brands as the chemical reactions within the arc tube (which create the light and spectrum) deteriorate over time. Unlike the sun, man-made lamps do wear out. Plants are quick to recognize these subtle changes. For example, think of putting an outdoor vegetable garden in a semi-shady spot. Sure, the plants may grow, but not to their optimum potential.

 For fuller, thicker vegetative growth and greater yield, lamp replacement should be part of a regular maintenance schedule. Keep old working lamps for troubleshooting your system or as a temporary replacement if lamps burn out.

When growing indoors, light intensity and spectrum become even more important. Simply put, the quantity and quality of light are the most critical factors associated with successful plant growth. Regular lamp replacement is essential.

Chart based on burning Metal halide lamps for 24 hours and burning HPS lamps for 12 hours.

The spectral distribution chart is the best way to compare light sources. Brands that do not publish spectral distribution charts should not be considered legitimate light source for indoor plant growth.

Lumens, Kelvin Temperature, CRI, CCT, CIE Chromaticity. All these terms are standard lighting measurements that tell us how the light looks to the HUMAN EYE. These terms do not represent the quality of a light spectrum nor do they take into account the Mcree Curve.

Understanding CRI

Fixture spacing and position above the plant vary widely. Light output and coverage is greatly dependent upon fixture design and quality of the materials used. Please consult the fixture manufacturer for recommendation on fixture spacing relative to plants.