{"id":8511,"date":"2023-04-22T17:36:53","date_gmt":"2023-04-22T15:36:53","guid":{"rendered":"https:\/\/marijuanagrowing.com\/?p=8511"},"modified":"2024-01-31T13:36:49","modified_gmt":"2024-01-31T12:36:49","slug":"light-lamps-electricity-chapter-17","status":"publish","type":"post","link":"https:\/\/marijuanagrowing.com\/light-lamps-electricity-chapter-17\/","title":{"rendered":"Light, Lamps & Electricity – Chapter 17"},"content":{"rendered":"\n
Light is essentialfor cannabis to grow strong, healthy medicine. All plants grow and evolve under Mother Nature\u2019s sunlight and care. Plants are accustomed to natural sunlight and have adapted to her spectrum, intensity, and photoperiod. Light is comprised of separate wave\u00adlengths or bands of colors. Each color in the spectrum used by plants sends them separate signals, promoting a different type of growth.<\/p>\n\n\n\n
Sunlight <\/strong>contains 4 percent ultraviolet radiation, 52 percent infrared (heat) radiation, and 44 percent visible light. Midday during the bright summer growing season, light intensity can top 8640 foot-candles (93,000 lux), but cannabis plants use about half the energy found in natural sunlight. *One nanometer (nm) = one billionth (109) of a meter. Light is measured in wavelengths; the wavelengths are mea\u00adsured in nanometers.<\/p>\n\n\n\n Electromagnetic radiation spans a broad range of wavelengths. Gamma rays with a wavelength of 105 nm are at the far blue end of the spectrum and radio waves with a wavelength of 1012 nm are at the far-red end. Red light has a longer wave\u00adlength. The photons vibrate slower and contain less energy. Photons in the far blue ultraviolet (UV) visible spectrum have shorter wavelengths and contain more energy. The human eye sees only \u201cvisible light\u201d (wavelengths between 380 and 750 nm) a small part of the entire spectrum. Visible light wavelengths (light spectrum) appear to people as all the colors of the rainbow. Visible light is measured in foot-candles (fc) and lux (lx). Lumens are the measure of visible light emitted by a light source.<\/p>\n\n\n\n Lumens measure \u201cluminous flux,\u201d the total number of packets (quanta) of light produced by a light source. Luminous flux is the quantity of light emitted. Unlike lumens, lux measures the area over which the light (luminous flux) spreads. For example, if 1000 lumens were concentrated in one square meter, the illuminated square meter would have 1000 lux. If the same 1000 lumens spread over 10 square meters, a measurement of 100 lux is registered on the 4 square meters.<\/p>\n\n\n\n Plants \u201csee\u201d other parts of the light spectrum than humans see. They respond to wavelengths similar to those that humans need to see, but they use different portions of the spectrum. Peak needs to occur in the blue portion (430 nm) and red portion (662 nm) of the spectrum, where chlorophyll* absorption is at the highest levels. Light used by plants is measured in PAR (photosynthetically active radiation), PPF (photosynthetic photon flux) (\u03bcmol\/s).<\/p>\n\n\n\n *Chlorophyll is the most important light-absorbing pigment in cannabis, but it does not absorb green light. Green light is reflected, which is why we see the color green. Other pigments include carotenoids (a group of yellow, red, and orange pigments) that absorb light energy. Other pigments (e.g. zeaxanthin [red] and phycoerythrin [red]) absorb different wavelengths. Each color of light activates different plant functions. For example, positive tropism*, the plant\u2019s ability to orient leaves toward light, is controlled by spectrum.<\/p>\n\n\n\n *Phototropism is the movement of a plant part (foliage) toward a source of illumination. Positive tropism means the foliage moves toward the light source. Negative tropism means the plant part moves away from the light. Positive tropism is greatest in the blue end of the spectrum, at about 450 nanometers. At this optimum level, plants lean toward the light, spreading their leaves out horizontally to absorb the maximum amount of illumination possible.<\/p>\n\n\n\n PAR watts are a measure of light energy (radiant flux) used by plants to produce food and grow. PAR watts are the measure of the actual amount of specific photons a plant needs to grow. Light energy is radiated and assimilated in photons. Photo synthesis is necessary for plants to grow, and is activated by the assimilation of photons.<\/p>\n\n\n\n UVA is the most common UV light. It has little energy and is least harmful of all UV light. Used in glow-in-the-dark black lights, UVA light is also used in phototherapy and in tanning booths.<\/p>\n\n\n\n Black-light fluorescent lamps emit ultraviolet rays through a dark filter and glass bulb, but they are not appropriate to grow cannabis. According to some sources, ultraviolet light is supposed to promote more resin formation on flower buds. However, all known experiments that add artificial UV light in a con\u00adtrolled environment have proven that it does not make any difference.<\/p>\n\n\n\n UVB is a very damaging form of UV light. It packs enough energy to destroy live tissues but not enough energy to be absorbed completely into the atmo\u00adsphere. Destructive UVB can cause skin cancer. Be careful when outdoors, especially in areas with damaged ozone layers in the atmosphere that let more UVB light pass through. These are high-risk areas for skin cancer.<\/p>\n\n\n\n UVC light is absorbed almost complete\u00adly, and within a kilometer of the atmo\u00adsphere. The UVC photons crash into oxygen atoms, and the result is ozone. In nature, UVC is transformed into ozone and later oxygen so quickly that it is difficult to capture. UVC light works well as a germicidal water purifier and bacteria-killer in food. It also works well to kill bacteria, mold, and pests on plant leaf surfaces.<\/p>\n\n\n\n UVC light (100\u2013280 nm) carries too much electromagnetic radiation, or energy (the hyper atoms are moving too fast), for plants to process; the energy is sufficient to force electrons away from atoms and rupture fragile chemical bonds.<\/p>\n\n\n\n UVC light is used in short, limited, regular applications to kill mold spores in growing and harvested cannabis. UV radiation is absorbed by oxygen in the forms O2 and O3 (ozone). The ozone layer of our atmosphere protects life on the planet from high levels of UV radiation.<\/p>\n\n\n\n UVA (315\u2013380 nm) and UVB (380\u2013315 nm) light help new branch growth and have a similar effect as blue light. Ultra\u00adviolet (UVA and UVB) light emitted by natural sunlight and plasma lamps has been proven to increase overall vegetative growth in cannabis by up to 30 percent.<\/p>\n\n\n\n In experiments, vegetative plants grown under plasma lamps that emit UVA and UVB light grew up to 30 percent more dry weight, and branching was much more profuse. Cells were stronger and the outer layer of cells was tougher, which discourages attacks from diseases and pests.<\/p>\n\n\n\n I have personally seen plants grown at 1000-foot (300 m) and 4600-foot (1400 m) elevation. The plants at 1000 feet (300 m) produced more and bigger flow\u00ader buds. The plants at 4600 feet (1400 m) were smaller, with thicker, stronger stems and smaller buds heavy with resin. Afterward, both crops were compared. The plants grown at high elevation had more resin, but it is unclear if that was because of more UVB light. There are many different explanations for heavier resin production, including cold weather and wind.<\/p>\n\n\n\n Random photons of infrared light (750\u20131000 nm) on the other end of the spectrum do not contain enough energy to promote plant growth. Infrared radiation is not absorbed by plant cells, because it lacks enough energy to excite electrons found in molecules and is therefore converted to heat.<\/p>\n\n\n\n Gardeners who use infrared heaters do not have to worry about light affecting plant growth. Infrared radiation is absorbed by water and by carbon dioxide in the atmosphere.<\/p>\n\n\n Blue photons carry more energy and are worth more PAR watts than lower-energy red photons. It takes from 8 to 10 photons to bind 1 CO2 molecule.<\/p>\n\n\n\n PAR watts in photons-per-second be\u00adcame the standard to measure horticultural lamp spectrum output. This measurement is called photo\u00adsynthetic photon flux (PPF), and is expressed in micromoles-per-second (\u03bcmol\/s). Today PPF is the accepted lighting and greenhouse industry standard.<\/p>\n\n\n\n Outdoors, plants receive natural sun\u00adlight\u2014100 percent PAR\/PPF. Green\u00adhouse and shade cloth coverings limit the amount of PPF. Look for the \u201clight transmission\u201d factor in greenhouse and shade cloth coverings to figure the amount of PAR\/PPF light available to plants.<\/p>\n\n\n\n Most artificial lights deliver only a part of the necessary light spectrum that cannabis needs to grow. A higher PAR\/ PPF rating guarantees that more photons will be available for healthy plant growth. Under artificial lights indoors, medicinal cannabis must receive enough intense PAR\/PPF light to grow well. Gardeners report that medical cannabis grown under intense lamps with high PAR\/PPF ratings is healthier and stronger, with fewer disease, pest, or cultural problems.<\/p>\n\n\n\n Sunlight on a hot summer day when the sun is at the highest angle in the sky produces light levels of more than 93,000 lux\u2014all the PAR light you could possibly need!<\/p>\n\n\n\n Outdoors, little can be done to change the PAR rating except to plant the gar\u00adden in a sunny location, and to shade the plants as needed. Greenhouses can be illuminated with HID light, but out\u00addoors we are compelled to work with Mother Nature during cloud-covered days. We can use greenhouse coverings and shade cloth to cool plants and de\u00adcrease intense light.<\/p>\n\n\n\n Indoors, artificial lightbulbs and tubes must supply intense light for medicinal cannabis to grow well. The lamp must have the proper spectrum and have a high PAR rating.<\/p>\n\n\n\n Indoors, generating intense light is expensive and requires knowledge to employ a bulb with the proper spectrum. Intensity is the magnitude of light ener\u00adgy per unit of area. It is greatest near the bulb and diminishes rapidly as it moves away from the source. High-wattage HID (high-intensity discharge) bulbs supply the most intense light efficiently, followed by T5 and T8 fluorescent, and CFL and plasma lamps. But remember that T5 and T8 bulbs can be placed four times closer to plants, which makes them much more efficient than HID bulbs, according to the Inverse Square Law (see below).<\/p>\n\n\n\n For example, plants that are 2 feet (61 cm) from a lamp receive one-quarter the amount of light received by plants 1 foot away (30.5 cm). An HID that emits 100,000 lumens produces a paltry 25,000 lumens at 2 feet (61 cm) away. A 1000-watt HID that emits 100,000 initial lumens yields 11,111 lumens at 3 feet (91.4 cm) away. Couple this meager sum with a poorly designed reflective hood that has lost its shine, and the garden suffers.<\/p>\n\n\n\n For plant growth, the brilliance of a lamp has a limited effect when it does not produce the proper spectrum. For example, the efficient 600-watt HP sodium lamps have the highest lumens per watt (lm\/W) conversion, but a color rendering index (CRI) of 24 and spec\u00adtrum of 2000 K to 3000 K. Even though these lamps produce more light per watt, plants can use only parts of it!<\/p>\n\n\n\n Lumens emitted <\/em>are only part of the equation. Lumens received <\/em>by the plant are much more important. Lumens received are measured in watts per square foot or in foot-candles (fc). One foot-candle equals the amount of light that falls on 1 square foot of surface located 1 foot away from 1 candle.<\/p>\n\n\n\n As explained earlier in this chapter, plants use the PAR portion of the light spectrum to grow. Artificial lights that produce the highest PAR rating with a high-intensity are the logical choice to grow medicinal cannabis. To find out which lightbulbs supply the most usable light for photosynthesis, refer\u00adence their color rendering index (CRI) and the Kelvin (K) temperature ratings. The CRI indicates how close the lamp\u2019s spectrum is to natural sunlight. The color temperature (spectrum) of the bulb is expressed in kelvins. Kelvin is an absolute measurement of temperature that indicates the exact color spectrum a bulb emits. Lightbulbs with a Kelvin tempera\u00adture from 3000 to 6500 will grow medic\u00adinal cannabis. These two figures, coupled with lamp intensity expressed in lumens, can approximate a PAR rating for lamps that do not have one.<\/p>\n\n\n\n The color rendering index <\/strong>(CRI) is a scale used to measure the ability of a light source to reproduce the colors of various objects faithfully in comparison to an ideal or natural light source, which means how true to life these colors appear in the visible spectrum when they are being illuminated with anything other than natural light.<\/p>\n\n\n\n The color corrected temperature <\/strong>(CCT) of a bulb is the peak Kelvin temperature at which the colors in a bulb are stable. We can classify bulbs by their CCT rating, which tells us the overall color of the light emitted. It does not tell us the spectrum (concentration of the combination of colors emitted).<\/p>\n\n\n\n Light is commonly measured in foot-candles or lux, two scales that measure light visible to humans, but do not measure photosynthetic response to light in PAR or PPF. Lumens are a measurement of light emitted from the sun or artificial light. Light meters that measure in PAR or PPF are very expensive and seldom used by medical cannabis gardeners. Foot-candle and lux meters can also be used to achieve an approximate measure of light available to plants. The foot-candle and lux readings are still valuable, because they record the amount of intense (PAR\/PPF) light spread over a specific area.<\/p>\n\n\n\n Using an inexpensive light meter to calculate lumens, foot-candles, or lux is a way to estimate the amount of light plants receive. But it does not measure how much light is available to plants.<\/p>\n\n\n\n The relationship between light emitted from a point source (bulb) and distance is defined by the inverse square law. This law affirms that the intensity of light changes in inverse proportion to the square of the distance. Light diminishes rapidly.<\/p>\n\n\n\n I = L\/D2 For example:
Sunlight energy arrives from the heavens as electro\u00admagnetic radiation. It is both wave and particle in nature. The smallest divisible particles of light are called photons. The brightness of light is equivalent to the number of photons absorbed per unit of time. Each photon contains a fixed amount of energy. The energy in each photon dictates how much it will vibrate. The wavelength is the distance moved by a photon during one vibration. Wavelengths are measured in nanometers.*<\/p>\n\n\n\n
Use the lux measurement to know how many lumens to give the entire area for complete illumination.<\/p>\n\n\n\n
\n\n\n\nUltraviolet (UVA, UVB, UVC) Light<\/h2>\n\n\n\n
\n\n\n\nLight Intensity<\/h2>\n\n\n\n
ILLUMINANCE (LUX)<\/strong><\/td> EXAMPLE<\/strong><\/td><\/tr> 93,000<\/td> Brightest sunlight at midday<\/td><\/tr> 20,000<\/td> Shade illuminated by a clear blue sky at midday<\/td><\/tr> 10,000\u201325,000<\/td> Overcast day at midday<\/td><\/tr> <200<\/td> Super dark storm clouds at midday<\/td><\/tr> 400<\/td> Sunrise and sunset on a clear day<\/td><\/tr> 40<\/td> Overcast sky at sunset or sunrise<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n\n LAMP<\/strong><\/td> WATTS<\/strong><\/td> INITIAL LUMENS<\/strong><\/td> MEAN LUMENS<\/strong><\/td><\/tr> MH<\/td> 1000<\/td> 100,000<\/td> 80,000<\/td><\/tr> SMH<\/td> 1000<\/td> 115,000<\/td> 92,000<\/td><\/tr> HPS<\/td> 1000<\/td> 140,000<\/td> 112,000<\/td><\/tr> HPS<\/td> 600<\/td> 90,000<\/td> 72,000<\/td><\/tr><\/tbody><\/table> Measuring Light<\/h2>\n\n\n\n
\n\n\n\nThe Inverse Square Law<\/h3>\n\n\n\n
Intensity = light output\/distance2<\/p>\n\n\n\n
Distance Intensity = light output\/distance2<\/p>\n\n\n\nFeet<\/strong><\/td> Centimeters<\/strong><\/td> Lumens<\/strong><\/td> Lumens\/Distance2<\/strong><\/td><\/tr> 1<\/td> 30<\/td> 100000<\/td> 100000\/1<\/td><\/tr> 2<\/td> 60<\/td> 25000<\/td> 100000\/2<\/td><\/tr> 3<\/td> 90<\/td> 11111<\/td> 100000\/3<\/td><\/tr> 4<\/td> 120<\/td> 6250<\/td> 100000\/4<\/td><\/tr><\/tbody><\/table><\/figure>\n\n\n