Lighting Technology Comparison Information

I see a lot of people posting threads asking what lights to use, LEDs vs this fluoros vs that. I've also had a number of people PM me now for advice on the topic after seeing my various posts, so I'll be outlining the FACTS behind the various lighting technologies. I will not include ANYTHING in this post that is not indisputably factual.

First I need to explain some common misconceptions about a few important topics. Lumens are one, and light penetration is the other. Lumens are a WEIGHTED measure of light. The weighting is based on the wavelength of the light. The weighting that is done for lumens is nearly the complete inverse of the weighting done for Photosynthetically Active Radiation (PAR). In fact, lumens counts many important PAR wavelengths as nearly nothing and weights them with a value near 0. Yellow and green are rated most favorably by lumens.

Light penetration is a real thing, but what causes it is frequently misreported. HID lights DO NOT PENETRATE BETTER than other light sources. Light penetration at a given wavelength (or set of wavelengths) is determined by EXACTLY one thing: the amount of light you are throwing across a given area. The reason why people THINK HID lights penetrate better is that MOST lighting technologies throw significantly LESS LIGHT, and if there's LESS LIGHT, you're PENETRATING WORSE. If you throw the same amount of light as an HID light over the same area, you will penetrate as well. If you throw MORE, you will penetrate better. It does not matter if you use LED, fluorescent, or halogens. If you throw more light than the HID light, you will penetrate better. "Lumens from a single source" doesn't mean anything either. A single source hung a foot away to cover a certain area isn't gaining any benefit from coming from a single source. You could move it closer, but then you're throwing the light over a SMALLER AREA. The fact that the light is coming from a single source is irrelevant; it's the area where it's actually hitting the plants that matters.

Now that we've gotten some basic information out of the way, on to the lighting technologies:

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High Intensity Discharge Lighting
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The long-standing gold standard of grow lighting. These lamps are better than most lighting technologies at converting input electricity to visible light. The two main types used for growing are High Pressure Sodium and Metal Halide. Another advantage of HID lighting is that it's quite cheap. You can buy 1000W of HID lighting for about 1/10th the price of 1000W of LED, and about 1/3 of T5s. They are also incredibly compact for the wattage; no other current technology can fit 1000W into as small a space as a 1000W HID bulb with the same efficiency.

The one major downside is that the bulbs and ballasts produce a significant amount of heat. This requires that you hang the light fairly far away and cool/vent the room very well. The bulbs also degrade faster than most lighting technologies and must be replaced fairly frequently. The heat factor can make HID a non-option for many smaller grows. The best way to deal with the heat is a high pressure fan through a sealed/vented reflector hood. That adds a lot of cost, however, and can be infeasible in some grow spaces.

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Fluorescent Lighting
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Fluorescent lighting is the butt of more terrible myths than I can count. Fluorescents can't penetrate, fluorescents can't this, fluorescents don't that. The most comical part of it all is that the mechanism by which fluorescents work is nearly identical to how HID lights work. A mercury-vapor arc lamp inside the phosphor-coated tube (it's not paint) emits UV radiation. This causes the phosphor coating to fluoresce and emit light at the desired wavelengths. HID lamps use a very similar mechanism.

I would guess that most of the myths about fluorescents come from old T12/T8 fixtures. But if you look up any information about them, you can immediately see why they're bad. They throw very little light over a very large area. The same is not true for all fluorescent lights.

CFLs are less efficient than HID, and are pretty costly to replace since the ballast and bulb are one unit. However, they WILL work. You simply need more wattage to grow the same amount. Figure on adding 30% or so wattage for the same results as HID, or covering 30% less area.

High Output T5s are a technology that people are starting to catch on to. Stated lumens/watt beats metal halide. It's still "lower" than HPS, but HPS gets a huge fake lumens boost by emitting mostly yellow. T5s can also be had in pure blue, pure red and a mix of blue/red (looks purple). These will give the T5s a MASSIVE PAR output advantage over HID. Many people are replacing their MH veg systems with T5s, and some people have started to realize they're perfectly capable of flowering, as well. The light output over an area with T5s is comparable to what you'll generally be doing with HID lights. Therefore, they penetrate as well. I can personally confirm from my grows that the bud which comes from T5s is just as good and dense as that which you get from HID. You will pay more for the same wattage as HID, though. MAKE SURE YOUR T5s ARE HIGH OUTPUT. Normal output T5s have half the intensity and are not good for growing.

Power Compact Fluorescents are a light I normally only see in aquarium technologies, but they seem to basically be a compact version of a T5 with similar efficiency.

Very High Output (VHO) fluorescents throw more light than their respective HO equivalents, but are significantly less efficient. Your total yield will go up, but your yield per watt will go down.

The one MAJOR advantage that all fluorescent lamps have is that they emit VERY low heat. I can put my fingers straight onto my HO T5s/CFLs without ill effects. They still WILL heat up an enclosed space, but good room venting can easily keep the grow room around ambient.

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LED Lighting
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LED is the technology of the future. And since it's from the future, it costs a lot more. A LOT more. About 10x the price per watt as HID. It's also indisputably better at growing plants watt for watt than HID. It also emits more light per input energy unit than HID.

BUT. LED's worst enemy is its own supporters. They frequently claim things which are just not true. UFO sells a 90W fixture with only about 73W driving the the lights and says it's equivalent to a 400W HPS because of the PAR output. PAR output matters, but SO DOES LIGHT PENETRATION. High PAR wavelengths don't penetrate better than low PAR wavelengths. Therefore, you have to throw the same amount of light in the first place, and use the high PAR wavelength tweaking capability of LEDs to BOOST the output over an equivalent output lighting of HID.

I will say this: 400W of LED will destroy 400W of HID in any test. It's not even debatable; LED grows usually get >1g/W. On the other hand, it's EXTREMELY difficult to say what wattage of LED will match/beat what higher wattage of HID. Since the PAR activity of the two lights are so disparate, and the only way to improve penetration is to throw more light, you will pretty necessarily end up with a situation where one will be VERY difficult to directly equate to the other and figure out that 332W of LED = 400W of HPS or whatever it may be.

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Incandescent/Halogen lighting
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These types of lights work off of a principle known as black body radiation. If you heat something up really really hot, it emits light. The spectrum it emits depends on the temperature of the black body. Obviously, this lighting technology is EXTREMELY inefficient and emits a ton of heat. You really shouldn't use these lights for growing as they're simply terrible in every way. CFLs even being worse than HID are about 5x as good as incandescents.

 

Forgot one:

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Sulfur/Sulphur Plasma Lights
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These emit a LARGE amount of green light, meaning most of the input energy is completely wasted. Green light cannot be used to grow plants. That's why you see those green bulbs/green LED fixtures for gardening at night. If you have pure green light, the plant doesn't detect it at all. The reason why is quite obvious: leaves are green. They are green because chlorophyll is green. Things which are green reflect green wavelengths. If something reflects a certain wavelength, it cannot also absorb that wavelength.

I'm sure they work to some extent, but I wouldn't expect better than HID from them by much unless they improved the heat issue, then it could be marginally better than MH. They will go nowhere for horticulture, though. LEDs and fluorescents will continue to improve in the meantime and by the time sulfur plasma tech is affordable, it will be vastly inferior to alternative technologies. Really it's already inferior to LEDs in just about every way for horticulture. Sulfur plasma is about the only thing MORE expensive than LED watt for watt.

The fact that these lights are "like the sun" also means nothing. Evolution is not perfect, and plants are not perfectly adapted to the sun's emissions. This is why photovoltaic cells are significantly more efficient than photosynthesis.

and another:

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Xenon Arc Lamp
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I've seen a number of threads asking if xenon headlight bulbs can be used for growing since they're advertised as "HID". They are not the same as HPS/MH HID lamps. They still operate on a similar principle, but the efficiency and longevity are not the same. The lifespan of xenon arc lamps is very low; in the 2000 hour range. They also emit quite a bit of heat.

The major use of xenon arc lamps in the world is for very high wattage intense light that is very color-neutral. It's a good technology for good color rendering, and also seems to be better than most lamps at extreme wattages, since you can get 15000W xenon arc lamps.

 

And feel free to post questions here. I'd rather answer things once than repeatedly.

 

CFLs are about 20-30% less efficient than HID, so 400W of CFL would only be as good as about 300W or so of HID. If you want to do a higher wattage fluorescent grow I'd recommend T5s. At lower wattages, HID lights are less efficient and closer to CFLs in efficiency.

 

It should be alright. I only have personal experience with Hydrofarm fixtures.

Ideally with T5s you should get the pure blue/pure red bulbs. 6500k/3000k definitely work fine, but the pure red/pure blue will work better. I've found one good place to get a specific type of pure red aquarium bulb:

Store Lighting Supplies T5 Bulbs

For veg and preflower, I'd mix blue/red then go all red for flower.

 

The problem with VHO tubes is that they are significantly less efficient than HO tubes. HO tubes are around 95 lumens/watt. The same tube in VHO mode is only about 66 lumens/watt. You'll be able to throw more light into the same area, so you'll get better results... but your yield per dollar spent on electricity will be lower.

Edit: I added a note about the VHOs to the OP.

 

VHO T5s are low efficiency compared to HID lights. They have an efficiency more comparable to ballasted CFL bulbs (around 60-66).

 

Based on the results of numerous grows around the world that I've seen online and/or in person, it seems that HPS lights produce the best results in flowering, as opposed to MH. MH is a very full-spectrum light. HPS is about the furthest thing possible from full-spectrum light.

I'd recommend using all red for flowering, based on the spectrum of those lights and reported results. Generally even pure red bulbs have some minor emissions in the blue range, so you're not missing it completely.

 

T5s emit more light per input unit of energy. More light is better than less light, therefore T5s are better than MH. You can also keep the T5s much closer, maximizing light available to your plants.

Switching MH systems to T5 for veg has become incredibly common. My local hydro store doesn't really sell MH anymore, but they move multiple 4,6 and 8 bulb T5 units on a weekly basis.

edit: in continuing with more light= better, ADDING a MH bulb to a fluorescent system will definitely improve results. Just as adding more T5s of an equal wattage would. There are grow situations I could imagine that would work better with the MH due to its compactness, though.

also the lumen numbers for the pure red and blue bulbs are very low. Lumens rates red and blue light at a fraction of its true value; the total photonic output of a HO T5 does not vary significantly with the phosphors on the bulb. So you can assume a true efficiency the same as a full-spectrum T5 that can be more directly compared to MH using the lumens scale.