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.

Author: Mr.Zog

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.

Contributed by: MedMan

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

400w HPS: 1 foot
600w HPS: 1.5 foot
1000w HPS: 2 foot

Author: BobbyDigital

How To Read Light Level With An SLR Camera?

Using your SLR camera in manual mode, you can measure light level. Set camera ASA speed to 200. Set camera shutter speed to 1/125. Hold a large, white card (or sheet of paper) in the proposed plant location so that it gets max illumination. Be sure that nothing but the white card is showing in the viewfinder. Adjust f-stop on camera (or lens) until camera meter reads “correct exposure”. f4 = 64 foot-candles, f5.6 = 125 foot-candles, f8 = 250 foot-candles, f11 = 500 foot-candles, f16 = 1000 foot-candles, f22 = 2000 foot-candles, f32 = 4000 foot-candles.

I use this technique to: Determine “hot” spots in the room, I put my youngest plants there. Determine “weak” spots – install reflectors as needed to bring up light levels. Determine when bulbs are getting weak, instead of “it looks dimmer than before”.

Author: ngc7579


Metal Halide Safety And Fixture Recommendations

HPS (High Pressure Sodium) lamps can burn in any orientation.

MH (Metal Halide) lamps come in three basic types:
*Base up (BU), which must be operated in the base up position.
*Horizontal (HOR), must be operated in the horizontal position.
*Universal (U), which may be operated in any position.

Orienting metal halide lamps in burning positions other than those specified can result in severe reductions in performance and potential nonpassive failure. Lamp life,light output and color can be affected by the burningposition. Some burning positions may need enclosed fixtures for safety reasons. When replacing ANY HID (High intensity Discharge) lamp, never touch the bulb with bare hands. HID lighting gets exceptionally hot and any oils from your skin left on the bulb will burn and can cause the lamp to burst.

Always use soft, clean gloves when handling the lamps. Observe extreme caution while foliar feeding any plants around exposed lamps. I suggest turning off any fans and ventilation while spraying the plants, any water blown onto an exposed, burning lamp can cause it to explode in your face. Be safe.

Author: Mr.Zog

How Do I Manipulate The Photoperiod For Larger Yields?

The only photoperiod manipulation from years of experiments that offered discernible improvements was this 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 environmental 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 6:00pm

Author: MisterIto

Can Black Lights Be Used For Growing?

Black lights will not work for growing cannabis. They 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; Fluorescent (Tube shaped), Compact Fluorescent (a Fluorescent 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: Black light type fluorescent lights, halogen, mercury vapor, ANY incandescent lamp (if it screws into a regular lamp, it won’t produce worthwhile buds). Exception, compact fluorescent mentioned above.

Author: Smokey D Dope

How Can I Improve The Air Flow In Air Cooled Light Hoods?

How can I improve the air flow in air cooled light hoods? Like many of you, I use Hydrofarm hoods for my lights. I also air cool them using the 4″ adapters sold by most hydro shops. Now, one thing you’ll notice when attaching those adapters is the “grating” over the location where the adapter goes. It doesn’t take a rocket scientist to realize that those slats are going to impede air flow. So let’s remove them and give a real boost to our air flow.

Step 1. Take down the light/hood and remove the bulb. Remove the mogul socket by removing the two screws. Remove the 4″ duct adapter. Step 2. Cut out vent, using a Dremel, Zip, or similar tool. Repeat for inlet vent. Step 3. Reassemble your hood (mogul, adapters, etc). Safety Note: Be smart, use safety glasses and don’t do this stoned.

Optional insulation: I use some of that bubble attic insulation (or hot water tank insulation – similar to foylon) you find at most home improvement stores to make an “insulating blanket” for my hoods – every little bit helps. Building a DIY high output air-cooled canopy.

Authors: ncg7579 and MoS

Should I Use A Light Mover?

Light movers are mechanical devices that, as the name implies, move an HID in a fixed pattern over a garden. A light mover can increase the coverage of a light by 140%. The real advantage is MUCH more light is available to the plants when the light is in motion. With a stationary light all that is shaded will remain in the shade, but with a mover the light will hit from different angles giving better coverage. Light movers are found in 2 configurations: spinning arms (kind of like a ceiling fan) and along a rail that moves back and forth. The rail version seems to be much more popular with growers, probably because it will work with an air cooled light Light rails come in a variety of lengths, but most can be cut to fit any application.

Most growers prefer a “smart rail”, that is, one that pauses at each end of the rail for a period. The biggest problem with air cooling a light on a mover seems to be dealing with air duct slack. Apparently, if the light is close to the tops of the plants, the duct may be dragged through the plants, thereby damaging them. Overgrow poster Ferret devised a solution: Use a curtain track, not a rod but the track that has all the little hangers inside that slides very easily. I screwed this to the ceiling of room and used light weight string to attach the air pipe to the little hangers in the track. As the light moved the track hangers moved along with the air pipe stopping the air ducting from dragging over your plant tops doing damage. The track cost about $15-$20 at any hardware or store. Simple to set up and it works .

Author: Bongaloid

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.


Author: Mr.Zog

How Do I Build my own Cool Tube?

This type of fixture is very versatile. There are many different ways it can be configured:

*hanging or mounted on a chamber wall
*open-ended drawing air from the grow or ducted to a separate intake
*passively or actively cooled

Tools Needed:
*Power drill with 1/8″ or 3/16″ drill bit
*4.25″ hole saw
*pop rivet gun (optional)
*flat head and Phillips head screw drivers

Keep in mind that the full list of materials you will need depends on the type of glass you get and the configuration you’re looking to build. Here’s the materials list with some pictures and approximate pricing:

· $3.99– Glass, either 4″ Pyrex tube (approx. 12″ long, 4” diameter) or “hurricane” lamp glass ($3.99 at Hobby Lobby, is 11 3/4″ long and 4 5/8″)
· $2.99– 4″ H/C venting starter collar
· $4.50– 5″ to 4″ venting pipe reducer (for use with hurricane glass only)
· $3.00-7.00– High-temp foil tape
· $5.00– Thermal pipe wrap (looks like woven fiberglass tape with no adhesive)
· $8.00– 4″ aluminum “dryer” ducting (hanging configuration)
· $2.00– 1/2 wood screws (box wall mount only)
· $3.00– pop rivets or small sheet metal screws
· 4″ (dryer ducting and/or Pyrex tube only) and/or 5″ (hurricane glass only) hose clamps
· “S” hooks (for hanging)

a. Hurricane glass tube
When working with the hurricane glass “chimney,” the irregular shape needs to be overcome so that it can be attached it to a reducer collar that will make up one end of the fixture. You may attach a reducer collar to a single end if you want an open ended design, or you can attach one to each end if you will be running ducting to both intake and exhaust ports.

The graphics concentrate on the exhaust end to which the bulb socket is also anchored. On this end of the glass (at the narrow “throat”) numerous wraps of thermal pipe wrapping are wound around the glass and secured with a couple of wrappings of foil duct tape. The wrapping should build up the throat to the same diameter as the opening in the glass – where it snugly fits inside the larger end of the reducer.

This will allow us to use a 5″ hose clamp to secure the edge of the reducer collar to this tape wrapped “cushion.” (Note: you can use foil tape alone for building this “cushion” but the thermal wrapping makes for a neater seal, and is less susceptible to heat. Also, if a hose clamp isn’t available, the reducer can be secured to the glass with foil tape.

If you use a hose clamp, you will need to make some 1″ slits in the edge of the reducer collar the glass fits in to allow the hose clamp to compress it enough to hold the glass securely)

Mounting the socket inside the tube
In the graphic, a length of pipe strapping bent in a “U” shape is used to hold the socket far enough inside the glass to place the bulb roughly in the middle of the glass. This glass, $3.99 at Hobby Lobby, is 11 3/4″ long and 4 5/8″ at each end. Notice this glass is symmetrical. Don’t try to use the asymmetrical hurricane lamp “chimney’s” available at Lowe’s or HD; they’re too small and aren’t shaped in a way that permits good air flow.

The socket is either screwed or pop riveted to the bottom of the pipe strap “U.” My light was made from a 150w HPS security light which used a “medium” base socket; this socket has two little screws in it that more or less lined up with the holes in the strapping.

As for the mogul base sockets used with bigger lamps, I don’t know what they have on the bottom of them so you may have to improvise a solution for mounting them. The ends of the strap are bent around to “clip” over the edge of the glass and then secured with a couple of wrappings of foil tape. If you’d like, a more permanent mount can be had by drilling a couple of small holes in the tapered throat of the reducer and attaching the ends of the strap with a couple of pop rivets.

Running the wires
The wires from the socket can be either run through your 4″ ducting which will attach to the other end of the reducer or you can drill a hole in the tapered part of the reducer to run the wire out of the fixture to the ballast.

Here’s how I actually have it done in my box. There’s no venting, it just mounts to a 4.25″ hole in the side of my flowering chamber via a starter collar which fits snugly inside the 4″ side of the reducer collar. I’ve got them held together with four pop rivets for a permanent connection. The tabbed end of the starter collar fits into the hole where the tabs are bent around the edge of the hole and anchored with wood screw to the box wall. (In my box, on the other side of this wall is my utility room with a 4″ 115cfm computer case fan sucking out the back of it.)

One could just as easily connect another reducer collar onto the other end of the glass exactly as the first side was with “S” hooks for hanging from above. This fixture could then have both intake and exhaust from outside the box.

Originally this is what I would have preferred to have, but as my flowering chamber is only 2’Dx2’Wx3’H, the wall mount actually did better for me.

b. Pyrex baking tube
(NIMBY) “Using a Pyrex (borosilicate glass) tube obtained from a glass blowing supply house or using a “Bake a Round” (eBay had a dozen for sale the last time I checked) one utilizes either one or two (pictured) 4″ starter collars instead of the 5″ to 4″ reducer collars. They are 14″ long and 3.75″ in diameter.”

“I stretched the aluminum ducting out and measured 16”. I then snipped the metal “ribs” and cut the ducting open. The glass tube will now just drop into the long run of ducting. The electrial wires run to the remote ballast through the intake part of the duct (exhaust could also be used depending upon the location of the ballast). I measured 2″ from each side of my original cut and snipped the metal ribs again but this time didn’t cut the aluminum foil. This allows me to open the ducting up like a “wing”.”

A couple of wraps of pipe wrap sealed with foil tape on each end you want to put a collar on should be used to keep from biting the metal directly into glass with the hose clamp (pictured). The socket is mounted inside the tube with pipe strapping just as in the hurricane style fixture. It can either be “clipped” and taped over the edge of the glass or better, pop riveted to the inside of the starter collar.

Simply stick the glass inside the end of the starter collar an inch or so past the bottom of the tabs to measure how far in to drill two holes 180 degrees apart, then use two pop rivets to attach the strapping

A note about pipe strapping: don’t get the thin wimpy stuff. Get the thicker heavy-duty strapping. The heavy stuff is still relatively easy to bend but holds it’s shape better and will hold the bulb and socket straight without sagging. At Home Depot they even have some copper pipe strapping (also known as “pipe tape” or “pipe hanger”) that is quite stiff.

Ventilation Performance
There are many different ventilation options available, since standard household ducting is used in the construction of the fixture. For those folks with bigger boxes or rooms, ducting in and out, “inline” duct fans are probably the best option.

For my little NewGanjaBoy-style setup, using the Hurricane fixture as part of the ventilation system of my box, a 115cfm computer fan does the trick. As for actual performance specs for different blowers/fans and light wattages, I’m afraid you’ll have to experiment. Here’s mine just to give an example:

-NewGanjaBoy-style three chambered box
-4 20w flouros in the mother chamber
-150w security HPS in the flowering chamber in original metal fixture with holes drilled in the top

Ventilation before Cool Tube installed:
-115cfm fan exhausting box
-4″x8″ intake port in the bottom of the veg chamber
-Two 2′ runs of 1.5″ PVC pulling air through the wall between veg and flowering chambers
-Two 1′ runs of 1.5″ PVC pulling air from over the HPS fixture into the utility room where it’s exhausting out the back.

Ventilation after Cool Tube installed:
-Two PVC runs between flowering chamber and utility room replaced with Hurricane Cool tube fixture
-ballast moved to utility room and housed in the original security light casing
-everything else is the same

Temps before Cool Tube mod:
Ambient temp: 80°F
Flowering chamber 1 hour after HPS fires up: 95°F (in direct light)
Flowering chamber 6-12 hours after HPS fires up: 100-105+°F (ouch!!)

Temps after Cool Tube Mod:
Ambient temp: 80°F
Flowering chamber 1 hour after HPS fires up: 85°F (in direct light)
Flowering chamber 6-12 hours after HPS fires up: 90°F (in direct light)

Please note that the wire to the bulb base must be a high temp fiberglass type, or the heat will eat up the wire and cause a running short. The thermal tape is a fiberglass electrical tape from most hardware stores. High temp fiberglass wrapped wire is available at any hardware or electrical store. It is imperative that you use it, as a smoking ballast is a real bummer to relight.

Authors: johnstone, NIMBY, Don’tTreadOnMe, sanclem and Smokey D Dope