in Lighting Mon Nov 25, 2013 1:16 am
by ozzydiodude • The Weird One | 2.084 Posts | 10103 Points

What are light cycles and how do I use them?

The amount of time your garden should be exposed to lighting depends on what 'cycle' your garden is in:

The 'Vegetative Cycle' of your garden starts with the sprout of the seedlings and can be continued indefinitely. In the veg cycle your garden will require a minimum of 16-18 hours of light and 6-8 hours of darkness daily. Since a given amount of light can only do so much, equal production can be realized in a smaller space with less plants, where the light is concentrated and the plants can grow more efficiently. Using more light helps additional co2 uptake. Since a plant can be kept in the 'Veg cycle' indefinately, many growers cultivate 'Mother' plants. This plant is used for clone starts and never produces buds, only new growth.

'Flower Cycle' or 'Bud cycle' is typically equal amounts of light and dark, 12 hours on, 12 hours off or 12/12. This produces a change in the plants metabolism simulating Fall, shorter days....less light. This is the cycle that the plants will show their sex. Usually, you'll be able to determine the sex within the first 2 weeks of 12/12. By the 3rd week most plants have developed healthy bud sites or pollen sacks. The plants will continue on the 12/12 cycle until harvest.

PAR for plants, Lumen for people.

While the lumens measurement is based on the sensitivity of the human eye to light, PAR Watts objectively measure the total watts of Photosynthetically Active Radiation (PAR) emitted by the lamp. It accounts for the nutritional value and is a direct measure of light energy available for all-important plant photosynthesis.

What is photosynthesis?

It has long been known that the green part of plants, when exposed to light under suitable conditions of temperature and water supply, intake carbon dioxide from the atmosphere and release oxygen into it. This gaseous exchange is the result of photosynthesis. The intensity, quality and daily duration of illumination all influence the amount of photosynthesis that takes place. Each type of plant, whether it's sun-loving or shade-tolerant, has its own rate of photosynthesis. More photosynthesis appears to occur in the orange, short red and blue bands of the spectrum than in the green and yellow bands. In general, the longer the daily amount of illumination, the more photosynthesis will take place.

How can I improve my indoor lighting?
I follow the thesis of UV's importance in potency, proven by my preference for outdoor pot properly cared for under optimal conditions to the same strain grown indoors under optimal conditions. High blue spectrum output, including some UV and near UV, relative to red spectrum output is necessary to achieve complete potential. My thoughts on environmental conditions impact on sexual disposition demonstrate the more favorable enviromental conditions, the more females nature wants in that location. Poor environmental conditions encourage male offspring in the hopes that their pollen will be carried off to the nice place where all the ladies are. I have found seedlings started under 7500K light along with my strict environmental control to increase female turnout ratio on a consistent basis. All this has me interested in testing out the new 1100 watt metal halide from Sunmaster as a potential replacement for my current setup. It provides greater PAR output than anything else you can plug in a 15 amp circuit along with significant blue spectrum and UV output to increase female turnout and THC levels.

What is a light cycle?

The amount of light and darkness the plant receives per 24 hour day. The cycle is often stated like 12/12 or 18/6 where the first number is hours of light and second is hours of darkness. So a plant on an 18/6 light cycle would have a timer set to turn the lights off for 6 hours. The way this affects the plant varies by strain, but a few general ideas can be assumed. Any more then 15 hours of light will hold the plant in a vegetative cycle, any less and it may begin flowering. The hours of darkness that a plant requires to begin flowering is genetically determined. The dark cycle must be fairly dark, no more light than a full moon would provide. A good rule is that if you can see your outstretched hand "in the dark" than its not dark enough. For the vegetative cycle, 18/6 or 24/0 both work well. Most agree that there is more growth with 24 on and Cannabis does not need a dark cycle. But there are advantages to 18/6 such as saved electricity and lower heat buildup. When you want to initiate flowering, the light cycle is usually dropped to 12/12-- equal amounts of light and dark hours. Moving gradually from 24/0 to 12/12 will work but is not needed. One idea to simulate a more natural daylength is to start flowering at 14/10 and eventually get to 12/12 to finish. This will extend the flowering period by approximately 10% and also increase yield. These terms are expressed under the assumption that a full 24-hour cycle is used. This is the natural circadean rhythm that all living things have evolved to use and varying from a 24-hour cycle should be treated as experimental.


It all depends on what light you are using, if it’s HID, standard fluoro or compact fluoro (I assume you're not using halogens!). For HID (HPS or MH) lighting, use roughly 30w per square foot, and for flowering use around 60w per square foot. This is merely a guide, your plant, light height; reflective surfaces etc make a huge difference on these numbers. For a small plant, below 1ft tall, I’d say you would need at least 25w of fluorescent light. I find that it isn't at all practical to use tube fluoro’s for the vegetative stage past 6 inches, as only the top of the plant is receiving enough light to carry out photosynthesis properly. Using an energy saving compact fluoro will help 'push' the light to the base of the plant, assisting photosynthesis. If the plant indicates it needs more light by growing slowly, and with small leaf petioles, you may need more light. Go with the basic rule of keeping the fluoro’s very close, and using roughly 20-30w per square foot for strong vegetative growth. If you can afford to over-light your grow room, why not? You wont regret it when your plant is bushy and healthy. If you feel that you need to only purchase a minimum amount of lights, you probably shouldn’t be growing. <br>Growing takes effort and money, and if you can't support a plants needs you might as well just forget growing until you can afford a proper setup. Skimping on lights is the biggest mistake a grower can make, because photosynthesis is so important to for a health plant.

What type of lighting is best?

Fluorescent or metal halide lighting is best for clones and seedlings. Metal halides are recommended for vegetative growth due to their enhanced blue spectrum which encourages bushier, more compact growth. High pressure sodium lights are better suited for flowering, but either can be used for the entire cycle with favorable results. Durotest Aquatinic 7500K bulbs are my choice for cloning, seedling and mother plant lighting, for which they keep growth sturdy and compact. I switch to SunMaster Cool Deluxe metal halide during the early vegetative stage through the stretching phase of early flowering to keep the plant compact. I finish off the plant cycle with Hortilux high pressure sodium lighting. They are extremely bright and efficient with superior dispersion.

HID vs. Fluorescents

HID (High Intensity Discharge) Lamps are: Efficient. They put out more light, with less energy usage, than any other type of illumination available to indoor growers. Bright. HID's produce more light than other types of indoor horticultural lighting. Expensive. HID's cost more than flourescents. They range in price from $50-$600 dollars. Hot. HID's produce considerably more heat than standard fluorescents. Fluorescent lamps are:<ul type="square"Inexpensive. Shoplight fixtures can be purchased for as little as $7. Compact fluorescent bulbs only cost a couple of dollars a piece. Locally Available. Most discount stores and home improvement stores carry inexpensive, fluorescent fixtures and bulbs. Fine for vegetative growth. Fluorescent bulbs put out plenty of light for plants growing vegetatively, including mothers, seedlings and clones. Some growers prefer fluorescents for vegetative growth because of the slower pace of growth and better root development. Fluorescents need to be in close proximity to achieve their rated output, which means their canopy penetration is more limited than HID's. Comparatively inefficient. 10 forty watt fluorescent bulbs use the same amount of energy as a 400 watt HID, but produce far less light. Since they use the same amount of energy but produce less light, the remaining must be given off as heat. Contrary to how it may first appear, fluoros actually run hotter than the equivalent wattage of HID-- they just disperse the heat over a wider area.

Jackerspackle's Lighting Coverage Primer

A very general rule of thumb is that your garden needs 50 watts of HID lighting per square foot of illuminated area. This rule ignores the shape of your garden, so the following is really a better guide: A 250 watt HID will illuminate a 2' x 2' garden. A 400 watt HID will illuminate a 3' x 3' garden. A 600 watt HID will illuminate a 3.5' x 3.5' garden. A 1000 watt HID will illuminate a 4' x 4' garden. From Jackerspackle, here's a different take on watts-per-square-foot/meter (WPSF). WPSF assumes that the bulb's intensity is equal over the entire grow area.. in other words each square foot/meter receives the same number of lumens. But in reality light diminishes rapidly the farther you go from the bulb (1/4 the intensity for each doubling of the distance). So each bulb has a limited range, beyond which you do not have good growth. For example, a growspace that's 2 x 10 feet would require 1000 watts if you go by the 50 WPSF guideline that's commonly mentioned.. But a 1000 watt bulb only covers an area about 5 feet across - meaning the edges of your garden will be dark.. A better choice in this case would be three 400s or two 600s. Another problem with WPSF is it assumes all bulbs have the same intensity. But 1000 watts of HPS is not the same as 1000 watts of fluorescents or (yuk) incandescents. Fluorescents have their lumens spread out over a long tube and are therefore dim.. incandescents have the wrong color spectrum and are also dim. Nor is a 1000 HPS the same as four 250 HPSs.. 250s don't have anywhere near the intensity needed to penetrate thick canopy or tall, bushy plants. (Don't even think about growing meter-tall plants with a 250.) I could go on, but here's a basic guideline for lighting a growspace for good growth using common HIDs: WATTAGE -- COVERAGE 1000 watt - 4 to 5 feet across (1.3 to 1.5 meters) 600 watt - 3.5 feet (1 meter) 400 watt - 2.5 possibly 3 feet (.8 to .9 m) 250 watt - 2 feet (.6-.7 m) 175 watt - small, less than 2 feet These numbers assume you have a good reflector around your bulb and also reflective wall coverings. You can increase the figures a bit if using multiple bulbs, due to their overlapping effect. You can also increase coverage using a light mover... I know this won't put to rest the old WPSF idea, but i hope it shed some light on the subject.

What distance should my light be from my plants?

For (artificial) light, there is a law that always applies known as the Inverse Square Law. It states that light diminishes exponentially in energy as the distance is increased from the source. A good example is that you might be getting 1000 PAR Watts at 4" from your light source, but that would change to 250 PAR Watts at double the distance (8"). This law makes it EXTREMELY important for indoor plant growers to get their light source as close as possible to their plants. The amount of light your plant receives is directly related to it's yield/flower density. The problem: Indoor lamps used for plant cultivation (HID - High Intensity Discharge) give off large amounts of heat, to such a degree that they could cause damage to the plant if put too close. Indoors, there is an optimum distance/height between the plants and the light source. This distance fully illuminates the whole canopy with direct light from the source, but is as close as possible to the plants for maximum lumen intensity. This will be called the OLH, for Optimum Lamp Height. Ultimately, to get the best light efficiency from your lamp, you want it at the OLH at all costs. But how can you get it there without causing harm to your plants with the abundant heat? First, try moving your light to the OLH and see what it does to your plants. If they have no problem, then you're fine. If you have a high output HID, this probably won't be enough. Next, try actively exhausting your light hood by hooking up a direct exhaust system to the hood, and then move your lamp to the OLH and see if the plants are O.K. If the plants still seemed affected by the heat, then you must add glass to your actively exhausted lamp hood. Glass will absorb/reflect/filter some of the light energy being emitted by the lamp. The number would seem relatively low, around 2-3% of PAR wattage, but it will effectively filter out almost all of what little UV-B is emmitted by the lamp. UV-B is believed, and has been shown, to have a positive influence on the potency of Cannabis. Overall, it would be beneficial for one to add glass if needed to keep their lamp at the OLH, due to the all-powerful Inverse Square Law; moving light farther away will greatly reduce the amount of energy being emitted and is reaching your plants (Light intensity is directly related to yield and flower density). Almost all glass offered today for insertion in air-cooled lamp hoods is tempered glass, which is regular glass with low amounts of impurities. If one was looking for the most efficient glass for their hood, quartz glass will allow the transmission of UV-B, but is not made specifically for light hoods. And also remember, that if you have a rectangular garden, it is important to position the longest side of the reflector parallel to the shortest side of your garden. (from FAQ by Head Rush)
Additional note: you should periodically inspect and clean your light hood and bulbs, especially after foliar feeding or underleaf spraying for insects. The dust and dirt that collects will definitely decrease reflectivity. Isopropanol alcohol, glass cleaner or water (and a soft cloth) can all be used to remove streaks, dust and spots. There are a number of factors which play a part in the temperature radiated from your bulb, watts, hood design and air circulation for example. A simple method of testing for temperature is to use the back of your hand; if its too hot for your hand, its too hot for your plants. Good ventilation is the key to getting your light closer to the garden. Editor's note: Recommended typical OLH distances: Flourescents: proximimty 400w HPS: 1 foot 600w HPS: 1.5 foot 1000w HPS: 2 foot

How can I safely work in the growroom at night?

Our plants need an uninterrupted dark period to trigger/continue the flowering response. Even a split-second of strong enough light can 'reset' the cycle of a less-stable strain (cultivar) which makes the plants see a dark period of less than 12 hours and could cause them to think they should be vegging instead. If you need to enter the growroom during the "night" or dark period, to spray or to do something else that requires the lights off, here is the safest way to do it without stressing the plants or making them think it's veg time, which, in some cases can make them turn hermaphrodite. Solution: Wire up a light socket near the door (so you can easily reach the switch in the dark) with a green light bulb. Find these at most home-marts for under a few dollars. Going back to grade 10 physics we remember that plants don't "see" (absorb) green light, therefore it can be safely used at night.

How do I manipulate the photoperiod for larger yields?
This information is provided as experimental data and not fact. The only photoperiod manipulation from years of experiments that offered discernible improvements was the following photoperiod adjustment made for 1 or 2 calendar weeks at the point of maximum flowering rate: Daylength of 21 hours, 36 minutes with a dark period of 12 hours. To accomplish this, you need a 7 day, 24 hour digital timer. During a 7 day calendar week on Earth, the "sun" only cycles 5 times. This permits easily switching back to the regular 12/12 at your discretion. You may want to only alter during peak flower production to stimulate the plant's metabolism. Using this photoperiod throughout the flowering cycle will cause this: A variety that takes 49 days of 12/12 to mature, won't see 49 - 12 hour dark periods under 21:36/12 until almost 10 calendar weeks have passed. The total increase in light energy is almost 80%, which will produce larger yields, if all of your other enviromental conditions are kept optimal. The total increase in flowering period is only 40%, half the potential room for improvement. This means you don't have to be perfect to win out. Selective application of the 21:36/12 photperiod for only 1 or 2 weeks extends the wait only 2 to 4 Earth days, which makes up the missing 2 complete day and night cycles each week on Planet Ito. This permits the additional light energy to be provided without purchasing additional equipment or overloading existing circuits, which maximizes the existing system's capabilities. The main advantage is that matched with co2 and optimal nutrition, the plants metabolism will increase dramatically. I have only successfully tested this photoperiod for two weeks. The potential for a net increase of 40% over the entire cycle (80% increase in light energy vs. 40% longer wait) is worthwhile. Don't be afraid! Day 1 - Sunday, 6:00am til Monday, 3:36am Day 2 - Monday, 3:36pm til Tuesday, 1:12pm Day 3 - Wednesday, 1:12am til Wednesday, 10:48pm Day 4 - Thursday, 10:48am til Friday 8:24am Day 5 - Friday, 8:24pm til Saturday.

Can blacklights be used for growing?

They can not. Blacklights do not produce the correct spectrum of light to grow plants. The only lights that currently produce the required color spectrum of light to grow plants are the following; Suitable for Growing: lourescent (Tube shaped) Compact Fluorescent (a flourescent tube with ballast included that screws into regular light fixture) Metal Halide (MH) Best for Vegetative growth, but it doesn't contain all of the spectrum needed later during flowering for truly outstanding buds. the light shines a blueish/white color High Pressure Sodium (HPS) Best for Flowering. Ok for Vegetative. shines a yellow/orange color. All can be purchased at your local home/lumber store. Not suitable for growing: lacklight type flourescent lights. ANY incandescent lamp (if it screws into a regular lamp, it won't produce worthwhile buds). Exception, compact flouro mentioned above) Halogen Mercury Vapor.

Is a dimpled or polished reflector better at reflecting light?

A dimpled pattern will be better, as they produce balanced light footprints, the flat polished type can produce hot spots and uneven light distribution. (snoofer) High quality reflectors have a 'hammer specular' finish (to distribute the light evenly) and titanium dioxide (for max. reflectiviety) paint. The surface feels slippery.

How do I position a rectangular hood in my rectangular garden?

The majority of light originates from the sides of the reflector, which are parallel with the bulb; this can be ascertained by simply looking at the pattern of light shining on the walls and floor. The sides of the reflector are angled, and on many hoods the light footprint can be easily adjusted to suit your requirements. So remember, if you have a rectangular garden, it is important to position the longest side of the reflector parallel to the shortest side of your garden.


HID lighting is generally accepted as a better light for growing cannabis for a few reasons...
· It has much better light penetration · It is much more powerful (higher lumen output)
· It is stronger in light spectrums suited for growing plants What can we do to combat these problems to make the most out of our fluoro’s?
· Use a good reflector. Desk lamp reflectors are perfect, along with coke cans (cut in half from top to bottom).
· Purchase lights with high energy saving capabilities (e.g. high watt ratings)to increase light penetration
· Purchase lights with suitable spectrum strengths for each phase of growing (eg warm white, cool white etc.)
· Keep the lights close to maximize intensity
· For good results, these lights must be used with a good quality reflector. They give of 360 degrees of light (in a 2D cross-section) but you will only really need 90 degrees of light (maximum). Building a reflector will help concentrate all the light to the area needed, instead of wasting it lighting up the ceiling of your grow room! Although you can successfully grow and flower a cannabis plant under a fluorescent, your results will be poor and you will most likely be disappointed. Use these lights only for seedlings and clones, and perhaps the vegetative stage of the cycle. A HID light is recommended for flowering.

Let's help each other, by spreading our knowledge of the plants we love
Scroll up

0 Members and 1 Guest are online.

We welcome our newest member: Meredith Lopez
guest counter
Today were 14 (yesterday 69) guests and 2 (yesterday 5) members online.

Board Statistics
The forum has 1194 topics and 20726 posts.

2 members have been online today:

disconnected MC Chat room Members online 0