Answers about CFL, HPS, How Much Light...

[Roughrider]

Although I'm still kind of a new poster, I keep seeing a lot of the same comments--many of which are answered an Dr. Khronik's excellent El Cheapo Guide to Lighting. But there are a few things I'd like to add in regard to watts, lumens, cfl, hps, and efficiency and how much light you need. Maybe this should be stickied?

Watts have nothing to do with light or growth. Watts measure how much power a light fixture uses to produce light. You can tell how efficient a light bulb is by looking at watts. A 23 watt CFL produces as much light as a 100 watt incandescent...even though the incandescent has more watts, it's useless. See what I mean?

What you care about is light...more specifically, light energy. That's what plants use during photosynthesis/growth. Light is measured in lumens. In my experience and reading, lumen amounts per sq. ft./sq. m. look like this

2000 lumens sq. ft./21500 lumens sq. m. = Absolute minimum for growth. You won't get much from this, especially after the plant has grown a bit. Not really enough to flower well.

3000 lumens sq. ft./32250 lumens sq. m. = Pretty Good growth. Enough light for the entire light cycle, although your yields may be lower.
4000 lumens sq. ft./43000 lumens sq. m. = Very good growth. Once you pass around 3500, growth rate and ability goes up fast.

Over 5000 lumens sq. ft./53750 lumens sq. m. = Optimal growth. Dense growth in all stages.

Keep in mind that using reflectors, using mylar or having flat white walls, and keeping your lights close to your plants keep you from wasting lumens. It's not just about having light, it's about getting the light to your plants. IMO, people ofter overbuy lights. This creates more light, but the light isn't always hitting the plants. And that creates more heat and ventilation issues, which causes stress problems.

That's why it's still impossible to tell anything about growth or yield based on just lumens. A guy that has an HPS that is too far away from plants that have no walls near them and no ventilation may get poorer results than a grower with CFLs that uses reflectors and has a couple of lights under the canopy in a well-ventilated spot.

HPS lights are often said to generate more heat than CFLs. That's not really true...it's just that they are more efficient at producing light, and there's a smaller surface area on the bulb itself for the resulting heat to dissipate. That means more ventilation. But the higher amount of lumens per watt means you use less power and get greater light penetration through your canopy. Still, I'm a believer that well used CFL's can give you great grows with less ventilation and heat issues. If you're in a small to very small area (less than 4 sq. ft./.25 sq. m.), I'd consider the advantages of CFLs in that way.

But HPS is more efficient. A typical 250 watt HPS bulb/unit will produce about 27,000 lumens. I've seen people use a 250w in a 3' x 3' room and get good results. That's 9 sq. ft. which = 3000 lumens a sq. ft. (Really, a 250w HPS is better in a smaller area.) to give you an idea of the difference in efficiency of CFL vs. HPS, think of this.

23w CFL = 1600 lumens = 69.6 lumens/watt
30w CFL = 2000 lumens = 66.7 lumens/watt
40w CFL = 2600 lumens = 66.3 lumens/watt

compared to

150w HPS = 14000 lumens = 93.3 lumens/watt
250w HPS = 28000 lumens = 112 lumens/watt
400w HPS = 50000 lumens = 125 lumens/watt
600w HPS = 90000 lumens = 150 lumens/watt

So you can see that HPS is more efficient than CFL...and as you get into bigger HPS bulbs, it becomes a lot more efficient. There's also fewer hassles with multiple cords and saved money on your energy bill. If you've got a big area and/or you can deal with the heat and ventilation, HPS is the way to go in flowering. Still, I'm a believer in small HPS lights and combo HPS/CFL grows...if you've got a 2' x 2' room, you can use a 150w HPS and 4 23w CFLs from Wal-Mart and get a terrific grow with very few heat issues.

Hope this helps some people. And, yes, I wrote it all.

Roughrider Reviewed by Roughrider on 11-13-2007. Answers about CFL, HPS, How Much Light... Although I'm still kind of a new poster, I keep seeing a lot of the same comments--many of which are answered an Dr. Khronik's excellent El Cheapo Guide to Lighting. But there are a few things I'd like to add in regard to watts, lumens, cfl, hps, and efficiency and how much light you need. Maybe this should be stickied? Watts have nothing to do with light or growth. Watts measure how much power a light fixture uses to produce light. You can tell how efficient a light bulb is by looking Rating: 5

[Dutch Pimp]

Good post. Well said.....:thumbsup:

[growbe]

A very good post when it comes to comparing CFL to HID in terms of Lumens and such but, plants "see" light differently than human beings do. As a result, lumens, lux or foot-candles should not be used to measure light for plant growth since they are measures used for human visibility. More correct measures for plants are PAR watts, PPF PAR and YPF PAR, although each in itself does not tell the whole story. In addition to quantity of light, considerations of quality are important, since plants use energy in different parts of the spectrum for critical processes.
Plants are sensitive to a similar portion of the spectrum as is the human eye. This portion of the light spectrum is referred to as photo synthetically active radiation or PAR, namely about 400 to 700 nanometers in wavelength. Nevertheless, plant response within this region is very different from that of humans.
The human eye has a peak sensitivity in the yellow-green region, around 550 nanometers. This is the "optic yellow" color used for highly visible signs and objects. Plants, on the other hand, respond more effectively to red light and to blue light, the peak being in the red region at around 630 nanometers.
Red light provides the most efficient food for plants. However, a plant illuminated only with red or orange light will fail to develop sufficient bulk. Leafy growth (vegetative growth) and bulk also require blue light. Many other complex processes are triggered by light required from different regions of the spectrum. The correct portion of the spectrum varies from species to species. However, the quantity of light needed for plant growth and health can be measured, assuming that all portions of the spectrum are adequately covered. Light for plants cannot, however, be measured with the same standards used to measure light for humans.
First, how do we measure light quantity for humans? The obvious way is based on how bright the source appears and how "well" the eye sees under the light. Since the human eye is particularly sensitive to yellow light, more weight is given to the yellow region of the spectrum and the contributions from blue and red light are largely discounted. This is the basis for rating the total amount of light emitted by a source in lumens.
The light emitted from the source is then distributed over the area to be illuminated. The illumination is measured in "lux", a measurement of how many lumens falls on each square meter of surface. An illumination of 1000 lux implies that 1000 lumens are falling on each square meter of surface. Similarly, "foot-candles" is the term for the measure of how many lumens are falling on each square foot of surface.
Clearly, both lumens and lux (or foot-candles) refer specifically to human vision and not to the way plants see light.
How then should the rating for plant lighting be accomplished? There are two basic approaches to develop this rating: measuring energy or counting photons.
PAR Watts for Plants
Watts is an objective measure of energy being used or emitted by a lamp each second. Energy itself is measured in joules, and 1 joule per second is called a watt. A 100 watt incandescent bulb uses up 100 joules of electrical energy every second. How much light energy is it generating? About 6 joules per second or 6 watts, but the efficiency of the lamp is only 6%, a rather dismal number. The rest of the energy is dissipated mainly as heat. Modern discharge lamps like high pressure sodium (HPS) and metal halide convert (typically) 30% to 40% of the electrical energy into light. They are significantly more efficient than incandescent bulbs.
Since plants use energy between 400 and 700 nanometers and light in this region is called Photo synthetically Active Radiation or PAR, we could measure the total amount of energy emitted per second in this region and call it PAR watts. This is an objective measure in contrast to lumens which is a subjective measure since it is based on the response of the subjects (humans). A PAR watt directly indicates how much light energy is available for plants to use in photosynthesis.
The output of a 400 watt incandescent bulb is about 25 watts of light, a 400 watt metal halide bulb emits about 140 watts of light. If PAR is considered to correspond more or less to the visible region, then a 400 watt metal halide lamp provides about 140 watts of PAR. A 400 watt HPS lamps has less PAR, typically 120 to 128 watts, but because the light is yellow it is rated at higher lumens (for the human eye).
Since plant response does "spill out" beyond the 400 nanometer and 700 nanometer boundaries, some researchers refer to the 350 â?? 750 nanometer region as the PAR region. Using this expanded region will lead to mildly inflated PAR ratings compared to the more conservative approach in this discussion. However, the difference is small.
While HPS and incandescent lamps are fixed in their spectral output, metal halide lamps are available in a broad range of color temperatures and spectral outputs. With this in mind, the discriminating grower can choose a lamp that provides the best spectral output for his specific needs.

[Dutch Pimp]

This is two examples of light spectrums: for 2 different light bulbs. The first one is a High Pressure Sodium bulb, the second one is a Metal Halide bulb.

[Gundari]

Got a question for you light smart guys ^^

as of late ive been reading about how i should be using a 5700 light spectrum bulb for vegging and a 2700 for flowering ( think those numbers are accurate, if they arent they are atleast close). I use all cfls and i was curious as to if there is a way to tell exactly what light spectrum the bulbs putting out by looking at the bulb itself? I bought the parts for and setup a rubbermaid box grow a while ago and ive just gotten into flowering and id like to make sure i have the 2700's in there. I know i could just go out buy some of them and put them in but id rather not waste the money if i already made the mistake of using them for vegging. So...anyone got an anwser for me? ^^

[Dutch Pimp]

Some manufacturers put the Kelvin temp info on the CFL bulb or package, but it seems like most don't. It's enough to drive a person nuts. Plus the confusing terms: "cool white" or "warm daylight". If you don't see the Kelvin temp number, you don't know for sure, otherwise, they all look alike to me....:stoned:

6500K=veg
2700K=flower

They do better with Floro tubes.

[Roughrider]

First, to growbe. Technically you may be right (although PAR watts don't account for differentials in energy to produce blue and red photons). But you're overcomplicating things for a grow light FAQ. If you've got lights in the correct end of the spectrum (blue light for veg growth; red light for flowering), lumen output is much, much easier to determine and almost as accurate.

The guys at Sunmaster--where you cut and pasted your info from, yes?--will give you all sorts of computations to discuss PAR watts and PPF PAR. But, realistically, the differences between that and lumen output if you're using the right bulb is fairly small...small enough so that doing the equation for PAR watts isn't worth it unless you're doing a grow over lots of square meters. And that's if you know how many PAR watts your bulb puts out; most people don't for a very good reason. Manufacturers usually don't list them. It's kind of a marketing ploy if you ask me.

Put it this way...a pretty typical 400w HPS puts out around 125 PAR watts. For top level growth, you need 135 PAR watts per sq. m.; 105 will go a good job; 75 will get you by, but you'll lose some yield. So your 400w HPS grow light will do a great job on .93 square m., a good job on 1.19 sq. m., and a mediocre job on 1.67 sq. m

But it's a lot easier to just look at the lumens...you get around 50,000 lumens from a 400w HPS. I said that 5000 lumens sq. ft./53750 a sq. m. gives you a top level grow, 4000 lumens sq. ft./43000 a sq. m. gives you a good grow, and 3000 lumens sq. ft./32250 a sq. m. gets you an okay grow with lower yields. If you use lumens instead of PAR, you get these numbers: .93 of a sq. m. for a great grow, 1.16 sq. m. for a good grow, and 1.55 sq. m. for a mediocre grow. Like I said, the difference in the calculations is small.

Still, you could argue that PAR is more exact...except very few bulb manufacturers list PAR watts for their bulbs. But almost all of them list lumens and color temp (kelvin).

So keep it simple. If you're going heavy into growth and have access to PAR watts...good for you. If you're buying your bulbs at Wal-Mart or a regular store or (my favorite) 1000bulbs.com...just go with the lumens and make sure your bulbs are in the right spectrum. To answer your question Gundari...some, but not all (or many) bulbs will list their spectrum. (Sometimes its listed like this--2700k or 2.7mk, which both stand for 2700 kelvin.) The best bet is to look at the box they came in. Barring that--lights for flowering are in the lower end of the visible spectrum. They'll look noticeably yellower or, as they say, "softer." Daylight bulbs--6500k is best--will be bright white. Hope this helps.

[Gundari]

Figured id get an anwser that was along the lines of "your outta luck" Mine are kinda a soft white...atleast thats what i think they are but i dont really have anything to compare against. Suppose next time im at lowes or somewhere similar to that ill look and see if i can find anything anything in the 2700k area. Ty for the help.

[growbe]

Who cares where I got the info. the fact is that I have done lots of homework when it comes to lighting like you. Most peeps just look at lumens "hey isn't this light bright, man I have to ware sun glasses!" and off they go to the races. We all know, well maybe not, that like you said in your first post (Still, I'm a believer in small HPS lights and combo HPS/CFL grows), dual spectrum works best for the entire grow. If you can't find out the par watts, call any manufacturer and they will tell you after a few forwards-it's not hard, just takes some effort, and not just searching these boards where 90 percent of the answers are: mh for veg, hps for flower-and get the most lumens-not!. I use to grow mh during veg and hps during flower. I use to go by lumens only but could not understand why my grows did not get any better/bigger when I went with the fancy/overpriced high lumen bulbs. Hmmmmm, I wonder why.
Anyhoo, yes I'm a firm believer of the KISS method, and there are plenty of great grows where people just look at lumens. Hell, my ave. yield under a 1000 watt bulb was around 34 oz's, and lumens was all I looked at. First time I went dual (600,400), same strain from clone-38 oz's and the plants were much healthier.
Here's a pretty good site-kind of old: Grow Marijuana FAQ, Cannabis cultivation - marijuana growing tips & photos
And the best damn 400 watt bulb on the mrkt. Phlips MasterColor Ceramic Metal Halide ~ CMH ~ HPS-Retro White
Peace and good luck to all.

[Roughrider]

It's great that you call up light manufacturers for PAR wattage and have 1000w grows. (btw...having two separate lights is often better because the intersection points of the two lights have an area that is receiving good light from two directions. It's like a Venn diagram.) But most people aren't doing grows that big. Lots of people live in foreign countries where they can't just call light manufacturers. And, again, you don't get any particular benefit from PAR watt information IMO. The people that are pimping PAR watts are grow light manufacturers. There are plenty of threads that discuss whether PAR is useful, but I'm just not seeing a whole lot of positive response from actual growers.

I'm glad you did better in a grow with a change in bulbs...but, honestly, what you're describing is a 10% difference in yield. And, as someone who has obviously done a lot of grows, you know that a ton of things can affect things that much...from having lights one inch closer, to having the dual light overlap I mentioned above, to a small change in water salts, to having a bulb that's been used twice before and has lost ten percent of its output.

For most people doing small to medium grows--let's just say under 1.75 sq meters or 20 square feet--you can make life a lot easier by using proper reflectors, keeping walls and surfaces close to your plants properly reflective, getting good ventilation. This is especially true with the small grows (under 6 sq. ft.) that a lot of people do here. My goal with this thread was to talk to them. Using lumens to compute lights needed is both easy and practical for them. Necessary light, ways to use all the light you have, not overlighting if you don't need to to avoid extra heat and stress...that's the type of practical information that I think people want. And I wish you luck with all grows, growbe.