What is Light?

Light is composed of very tiny high-energy particles called photons that are among the fastest traveling objects in the universe. They travel at 299,792,458 meters per second or about 186,200 miles per second! Their speed is about 100 times faster than the speed of electrons in a current of electricity. When we turn on a flashlight or an electrical device, to us, it seems to start instantly. But for light to travel from the sun to our eyes it takes an average of about 8.2 minutes for the photon to travel the 150,000,000 kilometers (or 93 million miles) journey. That’s real fast! Super fast speeds require high energy.

What is the electro magnetic spectrum?

Not all light is equal. Some photon particles have higher states of energy than others. Blue photons have a higher energy state than red ones. Photons, like electrons (electricity), xrays, gamma rays, ultra-violet rays, and all other tiny fast-moving energy sources can be placed in order or ranked based on their amount of energy. That order is called the electro-magnetic spectrum. All light visible to the human eyes lies between 380nm-780nm ranges of energy.

electromagnetic spectrum graphic

The Sun emits vast amounts of energy particles far below and far above the visible range. The range of solar energy, or solar radiation emitted by the sun spans from 280nm – 3000nm! Most of the radiation beyond the visible range, that is, from 780 nanometers all the way to 3000 nanometers is in the form of heat, we can’t see it, but we can feel it. Our eyes only perceive the visible range (380-780nm) and within that visible range we are most sensitive to green light compared to any other color. It is perhaps a characteristic of our early evolution in search for trees and plant life for food as hunters, foragers, and gatherers.

nanometer graphic

As for plants, they are the inverse of humans; they are most sensitive to the red and blue regions of the spectrum, and least sensitive to the green. That is the reason why most plants reflect green light (they look green to us) and absorb all other wavelengths. This next graph represents the theoretical light sensitivity curve of plants also known as the McCree Curve. The graph indicates that for the two principle reactors in photosynthesis Red and Blue spectra are important. The area suggests that red is needed in an almost 2:1 ration to blue.

What is Chlorophyll ‘A’ and ‘B’?

Clorophyll a and b graphic

This is the area that best represent the plants photo-catalytic response to individual points (wavelengths) of light within the spectral distribution chart. Chlorophyll operates most efficiently with the red and blue spectrum to capture light and convert that light energy into sugars. Pigments such as carotenes and xanthophylls are considered accessory pigments that contributing to the process of for photosynthesis providing a connection to certain green wavelengths (though particular green wavelengths are reflected by the plant). Carotenoids peak utilization in ranges from 440-525 (violet-blue-green spectrum) and they do serve to trigger secondary plant metabolic functions.

Photometrics: Measuring Light Quantity and Quality: So far the indoors lighting industry has been measuring grow light intensity primarily in lumens (sometimes in foot-candles, or lux). Lumens represent how intense or how “bright” a light source is perceived by the human eye. This lighting measurement is used in illumination applications such as in living or community space, street lighting, art exhibits, photography, movie studios, hospitals, etc. Its purpose is to measure overall quantity of light and not is not a true representation for lighting pertaining to plant growth since it is quite possible to have really bright light but in the wrong spectrum (color region) leading to poor plant growth rates.

PAR (Photosynthetically Active Radiation), by definition represents only the sun’s visible spectrum, 400nm-700nm and refers to the sun as the constant source of light. It does not include any radiation in the ultra violet region or beyond into the infra-red region of the electromagnetic spectrum. PAR is usually measured in micromoles (µM) . PAR is a great photometric measurement of sunlight, but is still not the best indicator of measurement of indoor lighting since indoor lighting quality (and quality) varies from source to source and comes nowhere close to the quantity or quality of the Sun. Two artificial lights of equal par value may differ in plant growth effectiveness. Therefore in order to make an informed and educated decision on what light is best for your plants a PAR value is not enough.

A PAR Graph is absolutely necessary so that we can see how that PAR Value (light energy) is distributed across the color spectrum. This is called a lamps spectral distribution. This way we can compare the quality/quantity of light produced between one or more artificial light sources.

Below are representative PAR graphs overlapped for three very different and distinct types of light sources: Plasma, High Pressure Sodium, and Fluorescent (Compact White Fluorescent) lamps. Notice how completely varied is their spectral output is among the different light sources. The peaks represent intensity and the area underneath them represents just how wide a spectrum that light emits. The fuller (wider) the spectrum is the better quality of light. We could also say the more intense, the better, since no artificial light comes close to the fullness and intensity of the output of the Sun.

Spectral Output & Distribution Graph

output and distribution graphic

PPF: Photosynthetic Photon Flux expressed in uMol/S (energy over time) is the actual total number of photons produced by the source of light per second in the PAR region. Extensively used by light manufacturers.

PPFD: Photosynthetic Photon Flux Density is measures in uMol/M^2/S. PPFD represents a field measurement (energy over time over distance) and is defined as the number of photons in the PAR region that fall on a square meter of target area per second.

In the absence of a Spectral Distribution Graph (SDG), engineers, industry experts, and technicians have been discussing new ways to convey the photo-metrics of a spectral graph through alternate methods. Darryl Cotton, President of Inda-Gro Lighting in San Diego, California (www.inda-gro.com ) has suggested a non-graphical representation by dividing the PAR range into three separate regions ‘V’, ‘C’, and ‘F’. And providing the output intensities for each of the three individual regions: Vegetative, Carotenoid, and Flowering represented in watts over par region (watts/ V,C, or F).

What is VCF?

VCF is a good alternative measure to best interpret indoor lighting spectra as it breaks down the PAR range into three sections most utilized segments of PAR for plant growth.

(V) Vegetative 400-520 nanometers range. • (C) Carotenoid 520-610 nanometers range. • (F) Flowering 610-700 nanometers range.

VCF CHART graphic

This new photometric tool was presented in early 2015 at Arizona State University’s Symposium (ASU) at the Controlled Environment Agriculture Center (CEAC) in conjunction with the USDA SCRI (Specialty Crop Research Initiative), LED project members from Purdue University, University of Arizona, Michigan State University, and Rutgers University. Say, for example a typical 400w induction light’s V-C-F reading is 45-25-55. That would mean that 45 watts are directly contributing to the PAR output of the Vegetative region, 25w are directly contributing to the Carotenoid region, and 55 watts are contributing to par output of the Flowering region (all other energy is being lost as heat, light creation, or resistance). Many new photometric tools are being developed to help indoor cultivators make better lighting decisions and thus create new light industry standards.

What is CRI?

CRI stands for Color Rendering Index (CRI). The CRI scale ranges from 0-100. It represents the ability of an artificial light source to illuminate an object as if it was illuminated under natural sunlight. A CRI value of 100 would indicate that the source of light illuminates an object to its true color as if it was illuminated by natural light. The higher the index score, the truer the color.


What is The Kelvin Color Scale?

Kelvin scale graphic


High Intensity Discharge: The number one cultivation lamps are HID lamps. These include HPS (High Pressure Sodium) and MH (Metal Halide) lamps, and CMH/LEC (Ceramic Metal Halides/Light Emitting Ceramics). They are the most common of the intense horticulture lighting sources utilized in both the commercial and hobby markets. Ranging from 100 watts to 1,200 watts.

Plasma Lamps: have among the best spectrum available, but they have relatively low intensity as compared to HID lamps and are relatively expensive compared to HID lighting. Currently as of this document there are plasma systems available in 330w-500w in power.

Fluorescents: are normally used in germination/sprouting and early vegetative growth. Their fuller spectrum and low heat output make them ideal for young tender plants, seedlings and clones. There are also very economical and highly efficient in electrical consumption relative to their light output. They come in many color hues from Cool White (ideal for vegetative period) to warmer (yellower) fuller spectrum Daylight colors.

Induction Fluorescents: Basically similar technology as the fluorescent except the driver is a magneto instead of a ballast. The driver in induction lighting was originally designed by Nicolai Tesla. One of the benefits is the long lifespan of the lamps. The issue with the non-US models is their ballast typically fails within 5 years (before you fully benefit from your investment), and the magneto-ballast is roughly 40% of the cost of the fixture. Inductions have a lower carbon footprint and a much lower impact on the environment. These are great vegetative lights, but typically bests used in combination with HID lights, or mix with other technologies in flowering rooms or rooms with large mother/donor plants. Induction fluorescents made in the USA are quality products and provide long term benefits of bulb replacement savings, operational costs savings, and heat savings for indoor gardeners.

LED Lights: LED stands for Light-Emitting-Diode. There are many types of diodes, some designed for illumination and some designed for horticultural use. Being the most efficient light sources in terms of converting electricity into light with minimal heat; the future is bright for LEDs. We believe that based on their superb efficiency alone, schools, hospitals, businesses, homes, etc., will all be lit by LED’s in the future. However as of today, there are only a few good LED brands in the world. LED technology is very specific to the intended application. A common mistake growers make is not properly identifying the correct application for their purchased LEDs. If you purchase a LED, you must choose a quality brand. The typically return on investments for LEDs is 2-4 years. LED’s are still in development and have not yet been adopted in most commercial application due to their lower intensity and initial higher cost.

As of this writing, we have seen, or tested, every major LED on the market targeted for horticulture use and have concluded that LED’s run roughly 15-17% more heat efficient to HID lamps watt per watt. This can save substantial sums of money over time in cooling capacity to indoor gardens and bulb replacement costs. LED’s have also shown to be an awesome research tool for horticulture growers. Manipulating light spectra and observing unique plant responses. In some research studies LED’s have been used to shorten a flowering cycle in floriculture, in other studies they have been used to stimulate a tomato plant to produce tomatoes with higher levels of lycopene which makes them more nutritious. LED technology is rapidly evolving, so keep an eye out for the newer and better models as they become available in the market place.

Square Inverse Rule

square inverse graphic

All light energy as it travels through space (distance), it loses intensity (brightness). When measuring light emitted from a source at a known fixed distance, we discover that light energy is exponentially lost as the distance is doubled. This effect is called the Square Inverse Rule. For example, if we have a measurement of 100μM (100 micromoles) of light energy from a lamp at 1 foot away and we double that distance to two feet and measure again we would only get a 25μM measurement—basically 1/4 of the original intensity we measured at 1 foot. The key to maximizing your light is to keep the light source as close as possible to your plant canopy while taking heat, footprint desired, individual plant needs, life cycle, and other factors into consideration. Light is the main driver for growth in any garden. With most reflectors, luminaries, or light systems, the farther the light is from the plant canopy the larger its light footprint, or coverage area. However, this larger footprint comes at the cost of losing intensity. That cost increases dramatically the farther the light is from the plants. There is a narrow margin of distance, a sweet zone, where light sources operate most efficiently.

Lamp Coverage: Footprint

This chart represents an average minimum and maximum optimal footprint for each of the different HID wattage levels when using the lamps as a single light source. The optimal distance from a plant canopy for a 1000w is two feet to six feet. For a 600w it is one and-a-half feet minimum to a maximum of 5 feet. For a 400w the ideal working height is 1 to 4 feet. Most other lighting allows the light source to be much closer to the plant canopy. Fluorescent and induction lights have cool enough lamps which allow the plants to literally reach and touch the bulb. Depending on the style of cultivation and size of plants, sometimes it is better to have multiple points of lower-wattage overlapping light, casting fewer shadows on the plants and shining from different angles.

Lamp Coverage graphic

Light technologies are constantly evolving. The latest improvements to arrive in the HID arena in 2015 have been the development of Double Ended (DE) bulbs in both Metal Halide and HPS presentations. These bulbs are brighter and last longer and have much better intensity maintenance than traditional HPS/MH Bulbs. Also, the introduction of newer, efficient, and fuller spectrum ceramic metal halides in the 315w range (and lower wattage) available in a variety of Kelvin colors for flowering and vegetative growth are making quite a big splash in the commercial and hobby industry. As for LED’s, the newer, higher wattage, full spectrum (white) LED’s have also taken the industry by storm. Come visit the Monster Gardens physical store, give us a call, or visit us online to keep up with the latest in indoor lighting technologies. Good Luck with your garden!

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