Given three lights of the same Lumen - (say 1100 which corresponds to 75W Incandescent, about 20W Florescent and around 15W LED) which would work the best for growing plants ?
I have a small greenhouse setup where I germinate seeds and get them started to have a head start for spring.
Is the answer different for aquarium lighting ?
These are fluorescent lights which have a donut shaped tube.As they are excited externally, there are no electrode pins penetrating the envelope allowing air to be drawn in over time and making the bulb fail. They have a theoretical life of about 100,000 hours with little decrease in lumen output compared to other types except led which also tend to have a slower decrease in output. They put out much less heat/lumen than sodium or metal halide arc bulbs so they can be closer to the plants.
Well, supposedly the daylight or grow-light fluorescents have the best spectrum for growing plants relative to regular warm white bulbs.
However in my experience, the big thing is getting ENOUGH light of whatever kind to your recently germinated seedlings so they don’t get leggy and funky is a bigger concern than the actual spectrum.
I got one of these compact fluorescent light fixtures for germinating mine indoors. “Compact” is a relative thing; the bulb is like 10" long, 5" in diameter, and DRAWS 200 watts, and puts out something like the equivalent of a 1000 watt bulb (7000 lumens).
you’re going to want a much bigger light.
using a light that small with create tall leggy plants that will probably not even survive, andd if they did, they would die when you put them outside.
another VERY important variable is the kelvin temperature. for germinating/vegetation period you are going to want something around 6500K.
to do this properly you are going to want to spend at least a couple hundred dollars.
i would suggest using t5 high output florescents rated at 6500K. they are the best bang for the buck right now. metal halide would be my second choice, but are not quite as efficient and you need a ballast, so you’re looking at more $$$
also depends on what you are growing and how much.
I’ve germinated hundreds of seeds, of various woody or veg-plants, and always found that putting the HO fluoro lights just inch or two above plants as they grew, raising lights as needed, until time for outdoors. I used a small fan blowing across bowl of water to reduce heat and help keep humidity up (plus strengthen the developing trunk), but my ‘greenhouse’ was a large shelf about 10’ long and 2.5’ deep, lined entirely with alum foil for best light coverage per watt (two sets of four-foot HO two-bulb fixtures. Acclimate the plants gradually (few days minimum) before placing into outdoors full-time. I found big difference between foil and no-foil use, fwiw, in amount of legginess/hardiness developed. Made a big difference with Japanese maples and woody species especially, if that matters.
For aquaria, if its a marine tank, it depends on if you are trying to grow coral (either hard or stony types). I grew corals of both types for several years for trading and used LOTS of MH wattage with fans for cooling, Ca-reactors, protein skimmers, etc. Exspensive! General ‘guppy-type’ tanks can be fine with just the usual off-the-shelf lights, IME, unless you want to have water-plants grow well. Then you will want to get the better, costlier, more frequency=specific light set-ups. Fresh water costs are typically much less than trying to grow coral and such, of course.
Herre’s a decent link that exxplains quite a bit of what you ask in more detail, fwiw. HTH.
The issue is not the lumens directly. It needs to be daylight spectrum for the plants to do well. You cannot grow plants on incandescent lamps no matter what the wattage, because the light color is no good. Daylight spectrum is about 6500K as stated.
Since the amount of light the plant receives has more to do with the distance than the strength of the source – Inverse square law of light – you can have lower luminosity if the light source is placed close. You need high wattages/luminosity if the lights are placed far.
I have a baby citrus tree doing well on 4 hours of sunlight+ a 9W CFL with a focusing reflector placed 4" from the plant. Putting out perfect dark green foliage growth. Loads of people will tell you you need “at least 23W CFL”. garbage. Anyone who tells you that a certain wattage is wrong, without telling you how far away the light is placed, has no idea what they’re talking about.
Lumens reaching the plants is the important factor. Color is not a big deal so long as it is a somewhat normal color; toward the warm (reddish) end is better for plants in the flowering stage, toward the cool (blueish) end is better for rapid vegetative growth. Plants will die under green light.
Go for the highest lumens, forget about color. A warm white or cool white shop light with higher lumens is better than a purplish “grow light” that gives a more correct spectrum by blocking some of its light output by filtering out certain colors.
Put the lights as close to the plants as possible without overheating the plant. White reflective material tends to be better than aluminum foil; the wrinkles in the foil can focus hot spots and burn the leaves. Mirrors reflect less light than a piece of white poster board. Try mylar if you want to get fancy.
Certainly you can fine tune a setup with high quality “real” grow lights from a place like a hydroponics store but best value for casual plant starting is just inexpensive fluorescent light fixtures from the hardware store. Hang them close, move them up every couple of days as the plants grow. A fan is good, and do harden the plants some before moving them permanently outside.
For seed-starting, as noted you want good light output which is more important than spectrum at this point. Cheap shoplight fixtures (for example, ones with two four-foot T8 fluorescents) will work fine if growing seedlings are kept just below the tubes (there are adjustable chains to keep plants at the right distance from the tubes).
Almost as important is to keep the growing area cool once seeds have germinated - if possible, no higher than the low 60s. This keeps seedings compact; warm temps encourage legginess.
I don’t have the optimal cool temps available, so I’m using a combination of fluorescent fixtures and LED lamps to provide good lighting. By not starting seeds too early, I make sure that plants can go out into the coldframe before they have too much of a chance to get big and leggy.
IMHO, special fluorescent grow tubes are a waste of money. A combination of cool white and daylight types work fine.