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Light Info,some Of The Basics

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I thought this might be suited for a sort of Indoors Beginners Questions section?

Translated from the Cannabis Mistress Miss J.(/Choppie) Original topic in dutch


A basicneed of a plant is light.

Plants need different light from just the light we can perceive.A normal light bulb doesn't have the right colour of light and often not the intensity needed to let your plant thrive.

Remember you are trying to imitate the Sun!

The lights most often used are HPS(High Pressure Sodium),HPI(High Pressure Iodine),Energysavers((CFL-I) and Fluorescent lighting.Of much importance here is that they have the right colour,which is indicated in Kelvin.


How long do the lamps have to be on?

Clones,seedlings and plants in vegetation need 18 hours of light and 6 hours of (complete) darkness(speaking in general,for more info view posts below).

To induce flowering the lightcycle will have to be changed to 12 hours of light and 12 hours of darkness.

Depending on the strain the first indication of sex(pistils or staminates) usually show after 1 to 2 weeks(there's also a thing called preflowering(primordia)but for this topic we'll stay to the basics).

The transition from 18 to 12 hours lighting can be done instantly from one day to the next by changing to 12 hours light 12 hours dark and then continuing this cycle.


When do the lights have to be on?

In general lighting at night has a few advantages :

- in winter you get the heat from the lamps in the coldest part of the day

-in summer you profit from the colder night

-electricity is at a cheaper rate


So if possible it's handy to to time your lights to go on later in the evening and profit from the colder evenings and mornings.A cycle of 17.00 to 11.00 for vegetation and 21.00 to 09.00 for flowering seems the best as climatcontrol is concerned.In winter you could make the flowerperiod a bit earlier 19.00/07.00 or 20.00/08.00.


How do i mount my lights?

Lights of different Wattages have a different lightingoutput.

In addition reflectors(hoods) will influence the surfaceshine.

A hood is sometimes adjustable and gives you the ability to adjust the reflector on both sides.

Factor this in when you're deciding how to mount your lights.


Can you grow under a ordinary light bulb or energy saver?

No,the Lumen output is too low and the colour is insufficient.(about the energy savers,this is from a while ago,so if there are noteworthy results to be gotten by newer versions by the microgrowers,please reply and i'll edit)


Can you grow under tanning lights?

Apart from this being very expensive,no.


Can you grow under an incubation light?

No,this gives off heat not light.


Can you grow under Halogen lights?

No(even if there are people who do),these give off too much heat and the wrong spectrum(they are better than ordinary bulbs).


Can you grow under Streetlamps?

No,even if they are Sodiumlights,usually they are low pressure and give off a too narrow spectrumrange of light.


Can you grow under Energy Savers?

These can be used in micro-grows to vegetate,but are generally far too weak to produce any real yield.


Can you grow under HPI?

Yes,the HPI even has a higher lumen output than Fluo(also more heatrelease!),but because it has a higher percentage of blue light it is best suited for vegetation but for flowering the plants need more red light and you would need to switch lamps ore add another lamp with a spectrum better suited for flowering.


Can you grow under Fluorescent lighting?

Yes, to use for vegetation this works well,but when used for flowering the yield will be significantly less.

The lightcolors(don't know if this is global) 11(daylight),21 (coolwhite),82 (warmwhite,flowering) are most suitable.

There are Fluorescent tubes in different lenghts :

-59cm = 18W

-90cm = 30W

-120cm = 36W

-150cm = 58W(circa 5200Lumen)

(The combination 1:2 warm/coolwhite seems to work best)

There is only enough light for the plants close to the tube,so the lamp will have to hang only a few centimeters from the plants and to get the best usage of the light you should really grow and bloom horizontally.


What is the best light for Growing?

White light with a little blue stimulates healthy growth,yellow and red light is important for the flowering stage.

For the rooting of clones and vegetating Fluorescent lighting is well suited.

Fluorescent lighting can be used for flowering(with the right colourcode) but the yield will be lower.

One advantage of Fluo is it produces little heat and therefore won't cause heatproblems.

In a too cold environment you are even more likely to have to apply extra heating.

HPS is the most commonly used and can be used for both stages.

They do produce the most heat.Energysavers fit between Fluo and HPS as far as lightoutput and heatrelease.


How many Lumen(lightoutput) does a sodiumlamp produce?

150 Watt = 14500 Lumen,(?uncommon)

250 Watt = 31000 Lumen,effective surface 0.5 m2

400 Watt = 55000 Lumen,effective surface 0.7 m2

600 Watt = 98000 Lumen,effective surface 1.2 m2

1000 Watt = 115000 Lumen,effective surface 1.7 m2


Distance between lamp and plant?

250 Watt : minimum 20cm

400 Watt : minimum 40 cm

600 Watt : minimum 50 cm

1000 Watt : minimum 90 cm

When using extra cooling(cooltubes,watercooled lamps,pc-fans under the bulb)the minimum distance can be diminished.

Fluorescent tubes between 5-10 cm.


-Which is the more reflective?Matt-White paint or Black/Whitefoil?

(reflectiveness from best to worst)

White Lime

White Primer

Matt White paint


High Gloss paint



Why does my growroom have to be absolutely impermeable to light?

We force a lot in our indoor growcycles.

This makes the balance a lot more delicate,as it seems.

It's a well known fact that plants can get pretty confused when the indoor darkening is not done well.

A slit or crack which always lets the light through can prevent the plants from going into flowering or cause them to go back to vegetation when already in flower,or generally cause a lot of strange stress-symptoms,like deformed leaves and the production of fluffy deformed buds with strange leavegrowth.

This is why it's highly advisable to check for leakage of light even if that means to crawl in your closet and spending some time in the growroom with the door closed :verrygood

Scattered light from the moon and stars will be less harmfull to plants outdoors due to the somewhat more relaxed,longer proces of vegetation and flowering there.

As it happens a plant that is too close to a streetlamp won't flower properly.So even outdoors too much light in the darkperiod can be influential.


Grtz Miss_J


edit Beekaa: placed my piece of info in the first post.

Light colours, and what they do:


Blue, vegging light

865,840,940,950,965 (the higher the last numbers, the higher the amount of blue)


This produces the colour light wich the plants receive in spring and early summer.

Similar to HPI(-t) light but even more blue (865).

The plant will respond in making lots of shoots and really short internodes.


This way the plant "thinks" she has enought time to grow and doen't rush into the air to get pollinated.

Instead of that she takes her time to make more shoots to get pollinated in a while :specool

ideal for making a good foundation for the plant to go into flowering.


This colour of light is not advisable to use in flowering stage of the plant.






Red, Flowering light

830,827,930,927 (the higher the last numbers, the higher the amount of red)


This is similar colour to the light emitted by the sun in late summer,

Similar to HPS.

The plant will respond in stretching a bit more, and stimulates the flowering hormones.

It also is needed to maximize your yield under Fluo-tubes.


This Way the plant "thinks" she hasn't got much time before she gets pollinated.

She will react in growing into the air, and make some buds before all her chances for pollination have failed.

In outdoor most plants will receive this kind of light in flowering. It is advisable to do the same indoor.

Facts have proven that this is the most efficient colour to flower under indoor.



When to switch and/or how to mix differences per growroom and plantstatus.

try to anticipate, example:


when you grow sativa's and your height is limited.. i would use only 865 tubes to prevent major stretching.


but when growing an indica and you don't want them to be lettuce-crops and let the light a little in then i would use a mix or even more red than blue for a while to stretch the plant a little.



edit Aad: any editadvice/additions welcome!If there should be an bit about inductionlighting(maybe too advanced for a newbietopic?) i'd rather leave that to Da Miss herself :smoke ,!

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that'z a nice topic,

clean and transparant... :verrygood



a small remark-

the amount of light in the growing cycle is 6 hours is told.

How ever there are species wich will show signs of bloom with 6 hours of night.

If you are unsure about the data of the plant, it is saver to work with 4 ore 5 hours of darkness.

This counts especialy for some outdoor strains.


greetz weetje

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Very true,thanks @weetje! :verrygood

I also left out the autoflowering species(ie Lowrider),which flower immediately regardless off the duration of light/darkness,as well as some other things,to keep it a basic indoor beginners FAQ-topic.

So it's probably wise to keep the first post not too complicated and pretty general,but any additional info in the reply's is very welcome indeed! :specool


Grtz. Aad

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good topic aad!


you are just a translation magician! and definately doesn't need good translations!

really valuable to opengrow!






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Thanks @Just 4 Fun(friend! :verrygood ).


I was hoping for some more add-ons by people with real experience with different kind of lighting.I have to confess i myself have done all my growing to date(clones in the distant past and seedlings in the recent) completely and only under HPS(at the moment a 400 watt Philips Master Son-T PIA GreenPower),but to try improve my male/femaleratio(more blue light in the vegetationstage seems too give more females),i will be vegetating my next growth (Sannie's Jacks) under a 400 watt Philips Master HPI-T Plus.

Grtz. Aad

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Guest DaMiss

Good one Aad! :bier

Is it an idea to combine this topic with the other two light topics on WF (in subform 'de Info'):

Lichtinfo: alles over licht. from Stijlloos and the one from Miss_J.


I know there are some great pictures in the one from Stijlloos.

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Can you grow under HPI?


so what are HPI lights ?


I have looked around and I am still at a lose



all the best and be safe



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Nice piece of information but I totally unagree with the part about reflecting... But that is probably a discussion we will always have...



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Is it an idea to combine this topic with the other two light topics on WF (in subform 'de Info'):

Lichtinfo: alles over licht. from Stijlloos and the one from Miss_J.

That's a very good idea,but will take some time to do it right :bier .I thought i'd start with a quick one ;)

Will think about it,next week i'll have some more free time.



HPI(High Pressure Iodine)lamps are very similar to the HPS(Sodium)lamps in lightoutput and powerusage,but the spectrum of light they give off has more blue in it.So they are more suited to vegging than flowering.

Question for you,the MH you have does that stand for Metal Halide or Halogen?



Just saying you disagree isn't very helpful,if you have good arguments for a different order or addition,might be better to list them here so people can make up their own mind?


Grtz. Aad

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Question for you,the MH you have does that stand for Metal Halide



Metal Halide that is what a lot of us use to do our vegging (more blue) I grow under both at the same time High Pressure Sodium and Metal Halide


I use to change the bulbs one to veg one to flower


but now I will use a 1000 watt MH with 2 - 400 watt HPS to veg and flower, I have been doing this for about 3 or 4 years now and I am very happy with it


3 years ago I stopped using reflectors and just hang my bulbs vertical and it has helped with cooling so much, I like the nake bulbs also because I can hang them deep in the canopy for better light penetration


thanks for the answer :bier




back when I used reflectors



all the best and have a great day



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Aad and friends,

Nice thread about a crucial topic. I use a six bulb 4' T-5 HO (high output) light fixture for vegging. It's a very bright light and my plants grow nicely with tight node spacing. It's worth considering. I've seen people do very nicely flowering under them but only if you've got a nice level canopy like with scrog. Also a comment about halogens. Indeed they are hot and not a good plant spectrum except: halogens put out UVB light which can be used to stimulate THC metabolism late in flower. Some people use UVB reptile lights for that also. I haven't ever done that but I have a grow friend who swears by it.



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I know this thread has been dormant for a while , but I would like to ask dequelo about the vertical bulbs without reflectors . You stated that it gets deeper penetration , was yeild increased or decreased or neither . I am fighting heat due to reflectors and would love to remove them .

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Omg why didn't i do this sooner???.Like start properly from the begging?? ive jumped the gun a bit?? nothing new there am afraid guys lol.Sorry if ive not supposed to have done things the way i did??.Any how ive just adjusted the lamp it was around 6inch from her main cola.I dont have a cooltube just a fan a 12inch 1??.Soz guys im all new??.So i've really got no technical extraction im set her with my window open which is were my grow is???.If things do get to warm i open another window/door.I know i cant do this in the futer when its summer?.I've attempted to rig up a bathroom fan but found it hardly sucked any hot aIR ??.It sucked alot of air through when i could feel it at the otherside of the ducting so was deffinately working???.I dunno so im better off withou unless i've been duing something seriously wrong.I hav it rite at the top under the bul/hud??.Just did not do enough in my eye's.??/ :D

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Although an old thread, but as it's pinned and covers the topic I have in mind, and is in the basicssection I'll blast away!


I am curious to know more of different light cycles.


What is the minimum dark time plant flowers with without revegging? Let's say after week 4 of flowering, would changing cycle from 12/12 to 13/11 or even 14/10 be safe to increase yield, no hermies or anything, or is it strain dependent?


Would changing 12/12 light cycle to 11/13 increase tricome production, and 13/11 increase yield?


Would sativa flower earlier with 13/11 and indica later? How bout hybrids, does it depend on which dominance the plant has?


Any feedback appreciated, especially experiments and successes with Sannie's Shop seeds and different light cycles.


This collective wisdom might guide future generation of growers and current beginners alike!




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just sprouted, on your comment about the 13/11 . I got that idea fro tj short and I tried it last year. I did not like it as well as 12/12. hesad in his article to try it yu wil like t. well tj "I don't like it at all. I go 4/7 on veg and12/2 n flower. works good for me

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I don't know where half of this info came from. But they were reputable sources or else I wouldn't have included them.


I make no claims to the veracity of the information. They are just taken from my notes. Think of it as food for thought, and if you want to know more, research it yourself.





The usual plant photosynthesis using chlorophyl works best from red light. There are two slightly distinct processes that both work best from red light. Both work well from red wavelengths from 610 to 675 nm, and one of them also efficiently utilizes wavelengths up to 695 nm. Most fluorescent lamps made for plant growth purposes usually produce most of their spectral output in the 630 to 670 nm range. These wavelengths are red, and not as visible as shorter red wavelengths in the 610 to 630 nm range typical of fluorescent lamps designed for maximum apparently visible red output. Therefore, plant-growing lamps are not as bright as lamps designed for general illumination purposes.


Since plant-growing lamps produce mainly the light blue light of the low pressure mercury vapor arc and deep red wavelengths, they usually have a light purple or purplish-pinkish color and are noticeably dimmer than white fluorescent lamps.


Although chlorophyl also utilizes blue light, it does not utilize blue light as well as red light. Other photosensitive chemicals such as carotene respond to deep blue and violet-blue light, and therefore some plants may need some blue light for proper health. However, plants will usually get enough of this from the violet-blue 435.8 nm mercury line from any fluorescent lamps that provide enough red light. Use of blue light by chlorophyl may be impaired in a few types of plants by colored substances in these plants that block blue light.


Plants will utilize orange and orange-yellow light, just not quite as effectively as red light. Fluorescent lamps rich in orange and orange-yellow output will generally work, but you may need enough lighting to be distractingly bright since human eyes are more sensitive to orange and yellow light than to the deep red wavelengths that plant lights are optimized to produce.


Please note that lowest-color-temperature ("warmest") tri-phosphor lamps (generally with rated color temperature at or near 3,000 Kelvin) produce lots of orangish red light around 611 nm, and will grow plants somewhat better than other white and near-white fluorescent lamps. These will grow plants almost as well as lights made for plants, but will look brighter.


Lights optimized for plant growth are low on green output, since plants reflect green light and cannot utilize green light well. One side effect is making red and blue objects look extra bright, and making green objects look an extra-deep darker shade of green. Part of the color-enhancing effect is from a relative lack of orange, yellow, and blue-green wavelengths that make green objects look slightly less green, with the presence of some nearly pure (only slightly yellowish) green light from the 546.1 nm mercury line. The shortage of orange and yellow light results in red objects looking vivid pure red. All this results in a general color-enhancing effect which is often considered a desirable side effect of plant-growing fluorescent lamps.




Well light useage is like most have said in two main spectrums. The first is 420-460nm that's pretty blue and that's the most efficient absorption of energy for vegetative growth. Also worth noting that plants with less blue light than they need get leggy. This is because parts of the blue spectrum allow them to control their internodal length.


The other part of the spectrum is the red side of things. The red is interesting because not just chlorophyll a and b get activated here this is also the realm of carotenoid(sp?) which are the yellow/auburn pigments. Now in the red range you'll get the most energy absorption somewhere between 640-650. Some why the 620 nm that make healthy plants? Well right around 620nm is a band of light which the plant use to change their metabolism from their night/growing/sleeping mode into an active photosynthetic mode. This takes around 2.5 hours for the plants to get enough of this light to actually start using the higher(640-650) red frequencies. So adding in these 620s won't actually give your plant anymore energy but it will more quickly catalyze your plants metabolism.


















Comparison of color temperature versus cholorphyll sensitivity graphs indicate that the general Earth plant prefers red light in a narrow band that corresponds closely with the color temperature of 2300K. 2100K bulbs will provide more energy to the plant then most 2700K HPS bulbs, both can be purchased, but if you could dial in the 2300K (the 650 to 660 nm range) that'd be best for inducing flowering hormones.


The blue range of light offers a wider swath for energy to be absorbed. Basically everything from UV up to about 500 nm (5000K) will be effective. Offering a lot of energy in this range will generally provide the highest values of PAR.


A combination of 7000K, 6500K, 6000K, 5500K, 5000K, 2700K, 2300K, and 2100K would be a very superior setup. LED offers the possibility for this configuration when you're talking the scale of hundreds of tiny little bulbs. The problem with LED is the casting distance, and you're not going to get the penetration power needed to grow big plants. This is an issue for the grower to come to terms with, but could be fine for the casual home gardener.

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