Switching back to MH last 2 weeks

Been reading where some are switching back to MH last 2 weeks of grow. They say it greatly improves resin output. Has anyone tried this & if so what happened?

2 Likes

@Laurap

It most likely will Laurap. It’s a fact that MH is far better than any other light.

I think you’ll find this interesting. Please read and let me know what you think

Types of Lights for Cannabis Growing - Different Marijuana Lighting Sources

Light for cannabis plants

Without light, cannabis plants cannot grow. In the countries in which marijuana grows best,
the sun is the source of light. The amount of light and the length of the growing season in
these countries results in huge tree-like cannabis plants. In most parts of North America,
however, the sun is not generally intense enough for long enough periods of time to produce
the same size and quality of cannabis plants that grow with ease in Latin America and other
tropical countries.

Sunshine is most intense at the equator where it is closest to the earth. Some of the largest,
resin-coated buds in the world grow beneath this blazing sun. So what’s this got to do with
indoor growing? Plenty. Light is one of the most basic needs of all cannabis plants and the
most often mismanaged.

Even the most experienced growers forget about the basic needs of a cannabis plant, especially light.

The answer to the problem of lack of sun, especially in the winter months, shortness of the
growing season, and other problems is to grow indoor under simulated conditions. The rule of
thumb seems to be the more light, the better.

The common incandescent light bulb emits some of the frequencies of light the cannabis plant can use,
but it also emits a high percentage of far red and infra-red light which cause the cannabis plant to
concentrate its growth on the stem. This results in the cannabis plant stretching toward the light
bulb until it becomes so tall and spindly that it just weakly topples over.

There are several brands of bulb type. One is the incandescent cannabis plant spot light which
emits higher amounts of red and blue light than the common light bulb. It is an improvement, but
has it drawbacks. it is hot, for example, and cannot be placed close to the cannabis plants.

Consequently, the cannabis plant has to stretch upwards again and is in danger of becoming
elongated and falling over. The red bands of light seem to encourage stem growth which is
not desirable in growing marijuana. The idea is to encourage foliage growth for obvious reasons.

Flourescent light tubes range in size from one to eight feet in length so you can set up a
growing area almost anywhere. There are two types of flourescent lights; standard and the
wide spectrum. They can be used in conjunction with one another, but the wide spectrum lights
are not sufficient on their own. The wide spectrum lights were designed as a supplementary light
source and are cheaper than the standard lights.

Wide spectrum lights emit the same bands of light as the standard but the standard emit higher
concentrations of red and blue bands that the cannabis plants need to grow.

The wide spectrum lights also emit infra-red, the effect of which on stem growth we have already
discussed. If you are planning to grow on a large scale, you might be interested to know that the
regular fluorescent lamps and fixtures, the type that are used in commercial lighting, work well
when used along with the grow lights.

These commercial lights are called cool whites, and are the cheapest of the fluorescent lights we
have mentioned. They emit as much blue light as the standard grow lights and the blue light is
what the cannabis plants use in foliage growth.

Intensity

Now we come to the question of intensity. Both the standard and wide spectrum lamps come in three
intensities: regular output, high output, and very high output. You can grow a crop of cannabis
plants under the regular output lamps. The difference in using the HO or VHO lamps is the time
it takes to grow a crop.

Under a VHO lamp, the cannabis plants grow at a rate that is about three times the rate at which
they grow under the standard lamps. People have been known to get a cannabis plant that is four
feet tall in two months under one of these lights.

Under the VHO lights, one may have to raise the lights every day which means a growth rate of ate
least two inches a day. The only drawback is the expense of the VHO lamps and fixtures. The VHO lamps
and fixtures are almost twice the price of the standard.

Now that you have your lights up, you might be curious about the amount of light to give you cannabis
plants per day. The maturation date of your cannabis plants is dependent on how much light they receive
per day. The longer the dark period per day, the sooner the cannabis plant will bloom. Generally
speaking, the less dark per day the better during the first six months of the cannabis plant’s life.

If your cannabis plants receive 12 hours of light per day they will probably mature in 2 to 2.5 months.
If they get 16 hours of light per day they will probably be blooming in 3.5 to 4 months. With 18 hours
of light per day, they will flower in 4.5 to 5 months. Its a good idea to put your lights on a timer
to ensure that the amount of light received each day remains constant.
Energy Emissions In Arbitrary Color Bands
40 Watt Flourescent Lamps
In Watts and Percent of Total Emissions
Daylight Cool White Gro-Lux GroLux WS
Light Type Band Watts % Watts % Watts % Watts %
Ultra-Violet -380 0.186 2.15 0.16 1.68 0.10 1.42 0.27 3.16
Violet 380-430 0.832 9.60 0.72 7.57 0.70 9.67 1.07 12.48
Blue 430-490 2.418 27.91 1.98 20.78 1.96 27.07 1.22 14.29
Green 490-560 2.372 27.38 2.35 24.67 1.02 14.02 1.24 14.49
Yellow 560-590 1.259 14.53 1.74 18.27 0.10 1.42 0.83 9.77
Orange 590-630 1.144 13.21 1.69 17.75 0.44 6.05 1.36 15.93
Red 630-700 0.452 6.22 0.81 8.47 2.86 39.55 1.86 21.78
Far Red 700-780 0.130 1.53 0.07 0.81 0.06 0.80 0.69 8.10
Total 8.890 100.0 9.52 100.0 7.24 100.0 8.54 100.0

Grow Light Guide

Horticultural lighting systems allow you to extend the growing season by providing your cannabis
plants with an indoor equivalent to sunlight. This is a great advantage for those of you who
appreciate having a year-round supply of fresh flowers, veggies and herbs. Artificial lighting
is also a great way to jump-start spring by starting your seedlings months ahead of the last frost.
There are three main types of horticultural lighting systems.

In summary, marijuana has a lust for light. HP sodium lamps produce 20% more light than super metal
halides. Horizontal reflectors yield up to 40% more light than vertical reflectors. Hammer or pebble
specular, anodized aluminum or white are the most reflective surfaces for hoods. Mirror finish is
the absolute worst reflective surface for a hood. Hang 400 watt lamps at 18-24” above garden, 600
and 1000 watt lamps, 24-30” above garden. Use a light meter. Grow the strongest, healthiest cannabis
plants that reach their maximum potential for resin production. Bright light brings big buds.

HID (High Intensity Discharge) Lighting

HID lighting is the most efficient way to convert electricity into light that is available to
the consumer. There are two types of HID grow lights used for horticultural lighting:

HID Light Efficiency

Metal Halide - MH

Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes
cannabis plant growth and is excellent for green leafy growth and keeping cannabis plants compact.
It is the best type of light to be used as a primary light source (if no or little natural sunlight
is available). The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond
this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to
finally burn out. If you compare their lumen (brightness) per unit of energy consumed, metal halides
produce up to 125 lumens per watt compared to 39 lumens per watt with fluorescent lights and 18 lumens
per watt for standard incandescent bulbs.

High Pressure Sodium - HPS

High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in
cannabis plants to increase flowering/budding in cannabis plants. They are the best lights
available for secondary or supplemental lighting (used in conjunction with natural sunlight).
This is ideal for greenhouse growing applications.

Not only is this a great flowering light, it has two features that make it a more economical
choice. Their average lifespan is twice that of metal halides, but after 18,000 hours of use,
they will start to draw more electricity than their rated watts while gradually producing less
light. HPS bulbs are very efficient. They produce up to 140 lumens per watt. Their disadvantage
is they are deficient in the blue spectrum.

If a gardener were to start a young cannabis plant under a HPS bulb, she/he would see impressive
vertical growth. In fact, probably too impressive. Most cannabis plants would grow up thin and lanky and in no time you will have to prune your cannabis plant back before it grows into the light fixture. The exception to this is using a HPS light in a greenhouse. Sunlight is high in the blue spectrum which would offset any stretching caused by HPS bulbs.

Common manufacturers of metal halide and high pressure (HP) sodium lights include Philips,
General Electric, Iwasaki, Venture, and Osram/Sylvania. Many of the manufacturers buy and use
the same components, often manufactured by competitors. Most often the bulbs have the exact same
technical statistics.

Lighting Chart - A guide for wattage per square foot.
HID Light Output Primary Growing Area Supplemental Area
100 watts 2’ x 2’ 3’ x 3’
250 watts 3’ x 3’ 4’ x 4’
400 watts 4’ x 4’ 6’ x 6’
600 watts 6’ x 6’ 8’ x 8’
1000 watts 8’ x 8’ 12’ x 12’

HID Lighting Helpful Tips

Hanging height: Due to the heat that is emitted from these types of fixtures, you should hang
them according to size. Smaller wattage systems (100 and 250) should be hung about 2 feet from
the tops of the cannabis plants. Medium wattage systems (400 and 600) should be hung around 3 feet
from the top of the cannabis plants. High wattage systems (1000 and up) should be placed at least
4 to 5 feet from the cannabis plant tops.

How long should lights run?

This depends on the type of cannabis plant. Most cannabis plants and vegetables need about
10 to 12 hours of light to promote growth. cannabis plants that produce fruits or flowers
will show improvement with up to 16 hours a day of supplemental light.

Fluorescent Lighting

This type of light is perfect for starts and seedlings. They are also popular for growing low-light
cannabis plants like herbs and African violets. Fluorescent lights are low intensity and need to be
placed within 8" (up to 15" for shade loving cannabis plants) of the cannabis plants to be effective.
They are a poor light source for flowering and budding primarily because of their low lumen output.

Daylight Cool White Gro-Lux GroLux WS
Light Type Band Watts % Watts % Watts % Watts %
Ultra-Violet -380 0.186 2.15 0.16 1.68 0.10 1.42 0.27 3.16
Violet 380-430 0.832 9.60 0.72 7.57 0.70 9.67 1.07 12.48
Blue 430-490 2.418 27.91 1.98 20.78 1.96 27.07 1.22 14.29
Green 490-560 2.372 27.38 2.35 24.67 1.02 14.02 1.24 14.49
Yellow 560-590 1.259 14.53 1.74 18.27 0.10 1.42 0.83 9.77
Orange 590-630 1.144 13.21 1.69 17.75 0.44 6.05 1.36 15.93
Red 630-700 0.452 6.22 0.81 8.47 2.86 39.55 1.86 21.78
Far Red 700-780 0.130 1.53 0.07 0.81 0.06 0.80 0.69 8.10
Total 8.890 100.0 9.52 100.0 7.24 100.0 8.54 100.0

Grow Light Guide

Horticultural lighting systems allow you to extend the growing season by providing your cannabis
plants with an indoor equivalent to sunlight. This is a great advantage for those of you who
appreciate having a year-round supply of fresh flowers, veggies and herbs. Artificial lighting
is also a great way to jump-start spring by starting your seedlings months ahead of the last frost.
There are three main types of horticultural lighting systems.

In summary, marijuana has a lust for light. HP sodium lamps produce 20% more light than super metal
halides. Horizontal reflectors yield up to 40% more light than vertical reflectors. Hammer or pebble
specular, anodized aluminum or white are the most reflective surfaces for hoods. Mirror finish is
the absolute worst reflective surface for a hood. Hang 400 watt lamps at 18-24” above garden, 600
and 1000 watt lamps, 24-30” above garden. Use a light meter. Grow the strongest, healthiest cannabis
plants that reach their maximum potential for resin production. Bright light brings big buds.

HID (High Intensity Discharge) Lighting

HID lighting is the most efficient way to convert electricity into light that is available to the
consumer. There are two types of HID grow lights used for horticultural lighting:

HID Light Efficiency

Metal Halide - MH

Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes
cannabis plant growth and is excellent for green leafy growth and keeping cannabis plants compact.
It is the best type of light to be used as a primary light source (if no or little natural sunlight
is available). The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond
this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to
finally burn out. If you compare their lumen (brightness) per unit of energy consumed, metal halides
produce up to 125 lumens per watt compared to 39 lumens per watt with fluorescent lights and 18 lumens
per watt for standard incandescent bulbs.

High Pressure Sodium - HPS

High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in cannabis
plants to increase flowering/budding in cannabis plants. They are the best lights available for
secondary or supplemental lighting (used in conjunction with natural sunlight). This is ideal for
greenhouse growing applications.

Not only is this a great flowering light, it has two features that make it a more economical choice.
Their average lifespan is twice that of metal halides, but after 18,000 hours of use, they will start
to draw more electricity than their rated watts while gradually producing less light. HPS bulbs are
very efficient. They produce up to 140 lumens per watt. Their disadvantage is they are deficient in
the blue spectrum.

If a gardener were to start a young cannabis plant under a HPS bulb, she/he would see impressive
vertical growth. In fact, probably too impressive. Most cannabis plants would grow up thin and
lanky and in no time you will have to prune your cannabis plant back before it grows into the light
fixture. The exception to this is using a HPS light in a greenhouse. Sunlight is high in the blue
spectrum which would offset any stretching caused by HPS bulbs.

Common manufacturers of metal halide and high pressure (HP) sodium lights include Philips,
General Electric, Iwasaki, Venture, and Osram/Sylvania. Many of the manufacturers buy and use
the same components, often manufactured by competitors. Most often the bulbs have the exact same technical statistics.

Lighting Chart - A guide for wattage per square foot.
HID Light Output Primary Growing Area Supplemental Area
100 watts 2’ x 2’ 3’ x 3’
250 watts 3’ x 3’ 4’ x 4’
400 watts 4’ x 4’ 6’ x 6’
600 watts 6’ x 6’ 8’ x 8’
1000 watts 8’ x 8’ 12’ x 12’

HID Lighting Helpful Tips

Hanging height: Due to the heat that is emitted from these types of fixtures, you should hang
them according to size. Smaller wattage systems (100 and 250) should be hung about 2 feet from
the tops of the cannabis plants. Medium wattage systems (400 and 600) should be hung around
3 feet from the top of the cannabis plants. High wattage systems (1000 and up) should be placed
at least 4 to 5 feet from the cannabis plant tops.

How long should lights run?

This depends on the type of cannabis plant. Most cannabis plants and vegetables need about
10 to 12 hours of light to promote growth. cannabis plants that produce fruits or flowers
will show improvement with up to 16 hours a day of supplemental light.

Fluorescent Lighting

This type of light is perfect for starts and seedlings. They are also popular for growing low-light
cannabis plants like herbs and African violets. Fluorescent lights are low intensity and need to be
placed within 8" (up to 15" for shade loving cannabis plants) of the cannabis plants to be effective.
They are a poor light source for flowering and budding primarily because of their low lumen output.

Incandescent Lighting

2 Likes

Thanks Will, im trying to fine tune my grow. Wasnt sure if flipping back at end of flower would cause too much stress with splitting stem, 48 hours darkness ect.
Im on 3rd grow & not quite where i want to be with my grows. First one i was terrified to do anything to them. Second grow i became more aggressive with them manipulating the branches, splitting stem ect. This grow im going to try what you did in first couple weeks of flower by crushing inside’s. Also ive yet to grow same strain twice. This time though i am regrowing an amnesia haze, a banana kush, a la confidential & a skywalker…

1 Like

I think there’s some good info in Will’s post, there’s also some pretty dated info there.

In your case @Laurap I believe you would indeed see an increase in resin production finishing under mh as opposed to hps. If you were flowering under a more balanced light spectrum it probably wouldn’t be as big of difference. But hps is definitely lacking at that end of the light spectrum. I haven’t done extensive dabbling there, but I would look to make the change about a day or two after you move to whatever you decide for ripening nutes.

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@Laurap

When your ready for bending you tag me ok and i’ll get you thur it. It really is no big deal and you will find that out after the firs onet… Just don’t go stir crazy on them… lmao

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you notice a difference when u split the stem @Laurap

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Honestly, not sure. On third grow & first time i have a strain that ive grown before. Ive got an amnesia haze that i plan on splitting stem & see if any difference from first grow. I split crystal but had nothing to judge by. Have to admit she sure was good!

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We’re you able to tell a difference @Laurap?

I’d never read this. I thought MH was heavy in blue spectrum (around 5500k) which is great for veg and we want reds close to 2500 or 3k for flower.

I had always assumed HPS was closer to the 3k spectrum and that’s why it was used…

I’m at 3-4 weeks flower. Should I plan on switching back to MH bulbs at some point?

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This was regarding my 400watt hps & side lighting. I probably couldve gotten a little more resin if i had switched back last two weeks. My tent us 4X4 & with the 400hps needed more lightining as they bushed up & budded. I just added some led side lighting. So if you do please tag me in. If you have a 600-1000 watt setup & tent is comperable in size to mine yoy should be fine.

Most hps bulbs will come in between 1700k and 2300k with a cri around 20. Lots of hid growers seem to favor going back to mh for last week or so of grow. Just don’t jump the gun switching.

1 Like

I use 600 watt magnetic hps ballist with 4500 Kelvin bulbs through the whole flowering process…
Since switching to rdwc I’ve been able to pull a lil over 2lb dry from a 3’x6’ table with 6 plants in a double scrogg …
Looking into cmh , but I’m planning on putting a 400 watt mh in the same hood as my 600 watt hps … so basically the best of both worlds… my hoods are sealed 8"air cooled xxxl so I have plenty of room for both bulb’s in my hoods… :grin:
Future experiments… this winter… I’ll let you guys know how it go’s… :wink:
The reason for going back to mh for the last 2 weeks of flower is because it has more ir and uv and that’s what increases thc… so that’s the reasoning… so I’m thinking why not have them both running the whole time…:grin:
:v::sunglasses:

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I got a question does anyone know if this is a good ballast kit

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Plus what are u suppose to use for veggin a MH or HPS

1 Like

Ya it’s fine. I prefer magnetic for hid ballasts, but that’s more for rfid than anything else.

Mh is what is most common for vegging.

1 Like

Ok thank you

I have that ballast in the 1000w model. MH for veg HPS for flower

So it’s an alright system how long have you had it

I think it’s more than alright. I’ve had these 2 going on three years.

I do however plan on upgrading to larger reflectors this spring, but same ballast.

U can get 1000 watt ipower on eBay or Amazon