cfl vs mh/hps energy consumption

Originally Posted by njhate

Output watts are the same, but i did read somewhere that a 1000W bulb draws (from the power company) roughly 1100 watts per hour. So the difference is pennies if you are worrying about the electric bill. I dont have a reference though... <snip>

Maybe that was true for cap/coil (magnetic) ballasts but "digital" ballasts are >98% efficient. In other words, a 1000W digital ballast uses 1020W of electricity - at most - to keep a 1000W bulb going. Digital ballasts are also proven to make bulbs last longer - up to three times as long - before so-called "lumen loss" sets in. So while the person using cap/coil ballasts is throwing out a $90 bulb every four months, the person using a digital ballast could use the same $90 bulb for a full year. So, if you pay a fair price for your digital ballast (I've seen some great deals lately), it can pay for itself - in bulbs alone - within 18 months. Modern technology is awesome, yes?

Speaking of "modern technology"; I can think of no reason why plants would "stretch" more under HID lighting than under CFL, as long as the bulbs are actively cooled (in an air-cooled hood or "cool tube"). You may be able to keep a CFL (or even a T8 or T5) closer to the plants but the added light intensity per watt given by HID lighting more than makes up for any inverse square effect due to distance. A 1000W HPS, for instance, penetrates four vertical feet at near full intensity. Conversely, a single 250W CFL penetrates 18"~24" at most (though you'd be using four of them). That said; HID lighting should always be actively cooled.

The single "good excuse" for not actively cooling an HID lamp is extremely low temperatures (in which heat from the lamp is necessary to warm the grow space). Even then, it's almost cheaper to turn the cooling fan(s) down to provide warmth during "day" (grow space ventilation - if any - should be separate from lamp cooling) and use a small electric space heater at "night". HPS lamps, in particular, are designed to operate in sealed (airtight and watertight; think "street light") enclosures; using them in a "cool tube" with minimal airflow shouldn't hurt them. Excessive heat will obviously cause the sodium core to break down a little faster - but at the point where this becomes a problem, the lamp could easily start a fire and a bad lamp would be the least of your problems (if you get my meaning).

As EmeraldPawn mentioned, it's a good idea to actively cool even LED lighting (and high-wattage CFL lighting should certainly be cooled). While there aren't currently any CFL-specific air-cooled hoods available commercially, most high-wattage CFLs use the same Mogul socket that HID lighting uses. If you wanted to take a small (4" duct) air-cooled hood or "cool tube" and rewire the ballast-specific plug to IEC/120VAC it's certainly easy enough to do. You could even buy the hood without the socket/cable and wire up your own using a quality extension cable and some easy-to-acquire parts. You could even make your own hood (if I had any interest in using CFL, I'd surely do this and post a tutorial).

I'd use 1/2" Foamcore for the top panel (to support hanging brackets made out of stiff wire or cable ties), the side panels (to support the standard HVAC flanges where the hood will connect to the ducting), and the mount for the socket (this must be made as "open" as possible for proper airflow through the hood). 1/4" Foamcore should be fine for the front and back panels (they don't see nearly the stress that the top/sides do). Thin Plexiglas or Lexan would make a good sheet "lens" on the bottom. How to join the "lens" to the body in a way that is airtight but still easily removable (for bulb replacement) is a matter for you to figure out. Maybe we can file competing patents! [I'm only half joking about that] I have no fewer than four different ways to do this competing in my head right now (this sort of sucks because I'm a very "visual" thinker and it's making it difficult to concentrate on writing). Now that I think about it, these materials are almost cheap enough to be disposable if you have no conscience and more money than brains (ha-ha).

Because the operating temperature of CFL isn't nearly as high as HID, there's no need to use aluminum, steel, or glass (which are used in HID hoods/enclosures because they're strong, obviously, but also because they're heat-resistant). This is why I've suggested Foamcore and Lexan (both of which are easy to work with, lightweight, and more than durable enough to survive many grows if not abused). 1/2" Foamcore is sort of expensive but I guess you could use scrap 1/4" "plywood" (luaun) or even Masonite for durability and glue/spray-mount 1/4" Foamcore on the "inside" (toward the light) for it's reflective properties (white Foamcore is "96% white" if I recall correctly). Anyway; everything you'd need is available at Michael's/JoAnn (arts/crafts store) or Lowe's/Menard's (home repair/construction store). Good luck and happy growing! Sorry for the long post.

The wattage is the sam on both bulb set ups. Ballasts are a different story. A 400 watt hps on a digital ballast will draw 460 watt, on a magnetic 490 watts. Cfl's have their ballasts on the bulb and depending on the bulb size the ballast will also take a certain wattage to run. A 150 watt Cfl will run at around 160-165 watts.

Its all math.

How do you figure 460W? I could see a small spike during "striking" (though most digital ballasts use a "soft start" routine which should be using less power at this point) but if a 400W ballast is rated as being >98% efficient, it should use a maximum of 400W*1.02 (or 408W) to run the bulb. Maybe I'm missing something. Still, I haven't seen a single digital HID ballast that is under 96% efficient (still only 416W). The "purple L" website claims a power input of 620W and output of 600W (~97%) for a 600W ballast. But this measure of efficiency is just the ballast (and doesn't consider the lamp itself turning that energy into light for your plants).

If you want to really talk "efficiency" (or, rather, "luminous efficacy"), it's lumens/watt (lm/W). All other things being equal, it's sort of where the rubber meets the road. CFL ranges between 50~70 lm/W; MH ranges between 65~115 lm/W (~90 lm/W @ 400W); HPS ranges between 85~150 lm/W (~125 lm/W @ 400W). So, basically, HPS is "better" than MH which is "better" than CFL (in terms of lm/W). As a matter of trivia, a Class G star (such as the Sun) is "only" ~93 lm/W. From atomic fusion. Makes HID lighting seem more impressive all the time, no?

By contrast, tungsten incandescent lamps are 5~20 lm/W (which makes it easy to see why they've been "replaced" by CFL). But considering that T5 - and even T8 - fluorescent tubes are 80~100 lm/W ("better" than any CFL) I have to wonder why anyone bothers to grow with CFL in the first place (except in a very small grow where a "normal" tube won't fit). LED might be a better choice for those applications, though. Screw-base 5.4W LED lamps reportedly have an efficacy of 100 lm/W. So in those small spaces, perhaps LED is "best" (if you can afford to buy enough of them to provide light for your plants).

So i'm gona return my other two 125w cfls and exchange the for a 400 watt mh/hps light and a shit load of fans for cooling down my grow room

No need for more than one fan; cool the lamp (not the room). Make sure the lamp cooling duct is well sealed (this is literally why duct tape was invented) and exhaust the heated air right out of the structure/home. If you've done the ductwork properly, the lamp run shouldn't pick up any smell at all from the flowers.

You'll want another (usually smaller) fan to refresh the air in the grow space (pulling it through a carbon filter and out of the structure/home; enough CFM to replace the air within 3~5 minutes). You can use a bigger fan if you put a speed control inline with it. Contrary to what I've read elsewhere on this forum, the air in the room does not need to be exhausted four or five times in one minute. That's just absurd!

Or you could seal the room entirely and use AC or a heat pump and dehumidifier to control temperature/humidity and CO2 system to make sure the plants can breathe...

The quick answer is that a 400W HPS will actually draw more juice than 400W of CFL bulbs.

Here's the reason:

CFLs typically draw EXACTLY their power rating, ie a 26W CFL will draw exactly 26 watts.

But HID lamps draw MORE than their power rating, because their ballasts also draw their own power. How much more depends on the lamp in question. The older magnetic core ballasts typically draw about 6-10% more juice, the newer digital ones less.

The difference isn't great, but it does specifically answer the question.

And of course the unasked question, 400W of HPS is typically going to be a LOT better for growing than 400 of CFL both because of better overall efficiency (ie more absolute light per watt), and better light spectrum (better quality light per watt).

CFLs do have their uses, but they're probably best used for really small grows, and/or ones where people are operating on "shoestring" startup budgets.

If you actually test your draw on a 400 watt digital ballast set up you will notice that the total constant draw will work out to 4.45-4.6 kw/hrs. When you fire them they will spike but then settle back down.

Between the bulb, ballast all your cables and wire these are the actual numbers I have seen and use when I calculate cost. Seems very accurate to me.

How much will 400 way metal halide cost to run a month 18/6 light schedule? I am NOOB!!!