How to choose the most cost-effective LED Grow Light

Here is a question about how to buy cost-effective LED Grow Lights we received from a reader. It is such a great detailed question and a great detailed answer that it deserves its own post.  So here goes:

This question came from a new grower in the market for a low-cost but effective LED Grow Light.

I’m looking for a good LED light and I want it to be cost effective. I’m new to growing. I got a cheap unbranded LED on eBay stated 300W but actual power is around 85W but for my next grow I want an upgrade. I’m growing a Sensiseeds Northern Lights auto right now. Just one plant but it’s filled out my 2 feet by 2 feet growing area. It’s in flower now and I have the light about 8 inches from the top of the plant. Since it’s an auto I run 18/6 lighting schedule. Is that the right way for auto in bloom?

I’m thinking about getting a new light. A big factor for me is that it’s cost effective and I get the most grams of high quality bud per watt.

I’m not growing for commercial use but I still want the best bang per buck (or £0.) I’ll grow only one or two plants at a time. Electric is a big part of the cost in the UK so I was looking for LED lights with two switches for grow and bloom as well as dimmable lights using pulse width modulation. Unfortunately I can’t find a cheap light with all these features. Do you have any recommendations?

BestVA have a 900W COB which is dimmable but it doesn’t have grow and bloom settings. It has a wide degree of light distribution so it could be hung lower with a lower light setting. i’m not sure about COBs though. lots of people like them because they emit white light to the naked eye but this means there must be some green light in the spectrum – much more than with conventional LEDs – so I worry they’ll be less efficient.
For about the same price I can get the Mars Hydro pro 2 (the 80 is about £150) or the Mars hydro reflector (240 for £50 or 480 for £100 but it might be an older model).

Wattage and LED Grow Lights–Does It Matter?

Then I came across a page comparing Mars lights and grams per watt. Mars claims that the best Mars lights significantly boost yields.

This could make a big difference if it’s genuine but how is it achieved? Is it just a marketing ploy? Platinum LEDs make similar claims about excelling at PAR per watt. The frequency spectrum graphs look very similar. Certainly not indicating huge differences between branded and unbranded lights. LEDs may differ in efficiency and I don’t know by how much. Reflector and lenses can all make a difference too but can these account for the massive differences in grams per watt?

Light is Key

Obviously nutrients and genetics make a difference too but I’m thinking solely about the difference the light makes. I’m only growing one or two plants in a small area so I can use a lower wattage and keep the light low so I don’t think I need to spend a lot on a high power light. But electricity costs over time I think will be the biggest expense. (I’m currently growing in soil – Canna Terra Professional with added perlite and blood, bone and fish meal – with Floranova series and PK13/14 nutrients and Photosynthesis plus. I’ll be adding molasses to help the microbes do their job better.)

Also – and this is a tough question – what about the law of diminishing returns? If i switch from the 85W light i have now to one that draws 170W true power will I get double the yield?

Your advice would be appreciated.

And here is the answer from our editor and resident expert Tim:

Congrats, sounds like the grow’s going well! Quite a few questions and points to address there. So I’ll just start with an explanation of wattage and LED grow lights.

When comparing LED grow lights wattage is really only relevant to your electricity bill. And it’s only the wattage drawn at the wall that you want to know. The wattage in the product name can refer to various different things, so can be a bit misleading.

Different lighting technologies convert the watts drawn at the wall into light more efficiently than others, LED lights being the most efficient at doing so. So an LED light drawing, say, 160W might be more powerful than an HPS light rated at 300W. And to confuse things even further, some LED lights are of course more efficient than others, so our advice at 420 Beginner is always to ignore wattage as a measure of brightness or intensity when it comes to LED lights.

What you need to look at is PAR values.

PAR, as you might know, is photosynthetically active radiation, referring to the spectrum of light a plant can actually use for photosynthesis. “PAR values” generally actually refers to PPF or PPFD which is a measure of how many photons of light (µmols, or micromoles) in that spectrum are falling on your plants per square metre per second.

Good manufacturers will provide charts/diagrams of PAR values with the light hung at different heights and how values differ across the footprint. PAR values are highest in the centre of the footprint getting lower toward the edges, but some lights give more even distribution than others. So that’s worth looking out for.

Yield Calculations are Hard to Find

Unfortunately, grams per watt, grams per joule and other measures of efficiency vs. yield are hard to find and rarely listed by manufacturers. So my advice would be to compare PAR values and wattage drawn at the wall, of the lights within your price range, and get the light with the best PAR values for the lowest wattage drawn. And if you’ve got any info about the light preferences of the strain you’re going to be growing, take that into consideration too.

Regarding spectrum, blue and red light are obviously very important to cannabis plants, but the wavelengths in between also have some value. So don’t worry too much if there’s some green light included in the spectrum. It’s not wasted light, and I’ve yet to see any light that’s so badly balanced that it’s emitting pointlessly, inefficiently large amounts of green light.

In other words, don’t discount COBs on the basis that they produce “white” light. So does the sun, and when wild cannabis gets enough of that it can grow to massive sizes!

By the way, ultraviolet LEDs are the least efficient, so don’t worry too much about getting a light with UV in the spectrum. By all accounts, just adding in a cheap UV aquarium light during flowering will get you better results for less money than UV LEDS.

Budget LED Grow Lights

For budget lights, the brands we tend to recommend are MarsHydro and Viparspectra. They tend to have better components and PAR values than many of the less established budget brands and you don’t see too many complaints about them from home growers. They mostly don’t have loads of features, but what they do, they do well.

Speaking of features, you’re right about dimmer switches. Most so-called dimmers just turn off some of the LEDs, which could negatively affect evenness of coverage and energy efficiency. A proper dimmer switch that could dial up the red light during flowering could help your electricity consumption, but proper pulse width modulation dimmers are rare at the budget end. Viparspectra have some models available with dimmers, like this one,  Cronus have some relatively cheap lights packed with features, and I seem to remember some Spider Farm lights having dimmer knobs.

Fixed Spectrum vs Dimmers and Other Debates

Also, bear in mind that there’s a lot of debate about whether you get better results from using a fixed spectrum for the whole grow (maybe adding in supplemental red and UV lighting during flowering) or using a light with bloom/grow or veg/flower switches. So maybe consider whether you definitely want dimmers. As far as I can see, which is the better method depends somewhat on what you want from your end product. For instance, if time is of the essence, not making a major change to the spectrum arguably gives you slightly quicker grow times, as the plants don’t need to adapt themselves to a new spectrum. Keeping a fixed spectrum and dialing up the red and UV arguably better mimics the sun when cannabis would naturally start flowering.

How many hours a day?

Regarding autoflowers, 18/6 is fine. But you could even go to 24 hours of light, in theory. As you probably know, regular cannabis needs 12 hours of dark to trigger flowering and not revert back to veg, but autoflowering doesn’t need that signal. However, many growers argue that giving your plants a rest period will still be beneficial. Maybe research a bit more and test a different light schedule on your next grow.

A quick word about DLI, daily light integral. I’ve explained it more fully in another comment on this post, but basically that refers to how much light a plant needs per day. For maximum energy efficiency, work out how many moles of energy per hour your light can emit and leave the lights on only long enough to give your plants what they need for the day. Moles per hour calculation would be: µmols x 60 x 60 / 1,000,000. (The µmols refers to the light’s PAR values.) Also, remember to calculate it using the PAR values at the correct hanging height for each grow stage, and add a bit of extra time to allow for the fact that PAR values will vary across the footprint.

Best LED Chips

Regarding the merits of more expensive lights, what you’re usually paying for (besides extra features) is a higher quality of LED chips and certain other components, such as the driver. Often, higher priced lights have passive cooling, too, rather than fans. The best LED chip manufacturers include CREE, Samsung and Osram; and a name brand diode tends to be better, in general, than no-name diodes. Meanwell is a trusted brand name for drivers.

DIY LED Grow Lights

Possibly the most efficient LED lights right now are quantum boards from Horticulture Lighting Group. They offer a great balance between price and power, with nice even coverage (more info at that link). To save extra money, you can buy them as kits or buy individual components and assemble them yourself. If you’re happy with that sort of DIY, there’s lots of info out there about assembling and customizing them. But you can also get pre-assembled, dimmable quantum board lights. We selected a mid-size light for our review, but there are smaller ones available too.

To get more out of your existing light(s), have a look into plant training methods. You can use techniques like Low Stress Training, Sea of Green, Screen of Green, mainlining, topping, fimming, super cropping, etc. to create a more even canopy height, create more bud sites and expose more of the plants to the light. Same grow light, but more of its photons hitting your plant. Those kind of methods can be a great way to increase yields without extra expense (besides cheap things like plant ties and stakes). We’ve got a post on some of the most basic methods here.

OK, I think that’s everything! 🙂 Hope it helps!