There’s a lot of info out there that is probably really helpful but that i don’t actually understand. Like you need growlights because they have wavelengths that ordinary lights don’t have. But also that any light with about 65000k should be good so what i am wondering i guess is can i just use whatever floor lamp with a 24W CFL globe that has a colour temperature of 65000k. Or do i have to use a special growlight. If so what growlights do you guys use because when i search online i can only really see temu ads which i don’t want so i don’t know where to buy from and what’s reliable and on top of that, what is actually available in Australia… I’m a bit overwhelmed by all the different things that need to be considered… help…

EDIT: My intention with this post is to provide beginners purchasing their first grow lights with what I think is the most efficient way to spend their money. I am not claiming that those who have previously purchased and used T5/T8 style lights are bad people who will have zero success growing anything. If you have purchased and use these lights I wish you the best. My point is that for those purchasing new grow lights I think there are much better options, for the same or very similar cost, that are more suitable for home gardeners growing different plants at the same time. I welcome comments that disagree and provide general reasoning outside of your own personal experience using a shop light.

TL;DR Don't buy T5/T8 "shop light" style LED grow lights and definitely don't buy the clip on wand/bendy style of LED grow lights. These lights can work (and even work well for specific setups) but there are now much better alternatives for a home gardener who wants to prepare a variety of different plants indoors in order to transplant for their summer garden.

The first light on my list was specifically selected as a better alternative to a pack of the common T5/T8 "shop" light style of grow lights for approximately the same cost ($45-$60). Compared to the shop lights it provides much more light energy, uses less electricity and perhaps most importantly: allows you to grow a variety of different plants that are different sizes as you don't have to keep it so close to your plants. You won't have to constantly adjust the height and will be far less likely to produce a bunch of leggy seedlings - it's far more forgiving in this respect. It also provides enough light to grow almost any plant through it's entire lifecycle so if you end up having to keep your plants indoors for longer (e.g a cold spring) you will have this flexibility - not so with the shop lights. The other options on my list generally provide increased efficiency and/or grow area but are obviously a bit pricier.

I recommend any of the following lights for approx. 2' x 2' - 3' x 5' grow areas. If you are growing in bigger areas I assume you know all this already and can make your own buying decisions:

1. Viparspectra P1000: Great entry level light for a 2' x 2' or even 3' x 3' (germination/initial seedling) growing area. Currently USD $58.

2. Spider Farmer SF1000: Another great light for a 2' x 2' or even 3' x 3' (germination/initial seedling) growing area. Slightly more efficient LED's than the Viparspectra P1000 above. Currently USD $90 or $76 for the version without a dimmer.

3. Spider Farmer SF2000: I personally have this light and really like it. Stated coverage is 2' x 4' or 3' x 5' (germination/initial seedling) but I think this latter value is a bit of a stretch. I would say max 2.5' x 4.5'. Currently USD $180.

4. Viparspectra P2000: Basically a larger version of the P1000. Great light if you need to cover a larger area, or just get two P1000's since they're on sale currently and work out cheaper. Currently USD $128.

Disclaimers:

• I'm by no means an expert - this is only my second year gardening and starting seeds indoors.

• Most of the supporting information I'm presenting is research done by others who are far more knowledgable than me. I have tried to balance supporting my arguments with keeping the post length reasonable but would be happy to provide additional support or make corrections if someone finds an error.

• I'm not sponsored by or affiliated with any of the manufacturers of the lights I recommend.

I found myself replying to the posts of so many new gardeners with this information so I thought I would make a post about it. As I mentioned above I don't consider myself an expert but my personality is such that I spent a lot of time nerding out about the science and literature behind grow lights and their effects on plant growth.

Light, Defined

Light is a way of transferring the energy into plants that they require to grow. This light energy is referred to as photons. For plant growth we are interested in the photons that fall within a certain wavelength range and we refer to this range as "Photosynthetically Active Radiation" (PAR).

Measuring Light

We measure the output from a light by measuring the number of photons that fall within the PAR range referenced above. This is usually measured in micro moles of photons - per square meter - per second (μmol/m²/s). The name for this value is often called the Photosynthetic Photon Flux Density (PPFD). If these two terms sound unnecessarily technical or complicated don't worry - all that's important is that you know that grow lights are measured by how much light energy they are providing to a specified area over a specified time period. Here is an example PPFD map (at 3 different heights) of a Viparspectra P1000 which I often recommend as a good light for a small area.

Since the area the light is designed to cover is 2' x 2', each square basically represents a 6" x 6" square area with the middle commonly getting more light energy than the outer/corner areas. Note that lowering the lights 4" from 16" to 12" above the plants makes a big difference - a 38% increase in light output. Generally lowering the light increases the light energy in the centre area but at the cost of decreasing the light spread and lowering the light energy towards the outer extents.

How Much Light Energy Do Plants Require?

Unsurprisingly the answer to this is: it depends. Some plants require more light than others and plants also require different amounts of light at different growing stages. There are resources provided with plant-specific information but in general:

• Plants in their seedling stage require less light than the same plants in their vegetative growth stage. Plants in their vegetative growth stage require less light than the same plants in their fruiting stage.

• Leafy greens generally require less light than fruiting plants/vegetables.

• Roberto Lopez, Ph.D., researcher at Purdue University, developed a thorough set of guidelines to recommend the average daily light integral (DLI) for most common plants. His research showed that in order to produce crops at a high quality, most plants require a minimum DLI of 12-20 mols/m2/day.

Important: It's important to note that we refer to the amount of light required by plants as their daily light integral (DLI). Emphasis on daily. I'm pointing this out because when we choose a grow light we will want to look at it's PPFD map, which shows how might light energy is transferred in:

micro moles per square meter per second

Again - when we look at the DLI of plants the amount of light they require is generally expressed as:

moles per square meter per day (24h)

Therefore we need to convert those PPFD values to ensure that our grow lights put out adequate light energy for the type of plants we want to grow and also enough light energy into an area that is large enough to cover the amount of plants we plan to grow. For example, it's not very useful having a light that provides high light intensity (lots of photons) but only covers a 1' x 1' area if our seedling trays and pots fill up an entire 2' x 4' shelf. Conversely it's just as useless to have a light that covers your full 2' x 4' shelf but doesn't provide enough light intensity.

How Long Should Grow Lights Be On For?

I found this specific topic to be the most esoteric with some information indication slightly different answers. For home gardening and vegetable growing I feel that it's safe to assume the following:

• Some plants are capable of handling 24hr light but some are not.

• Beyond a certain point, however, more light energy becomes wasteful as plants can only use so much until other things become a bottleneck for photosynthesis.

• We generally want more light-hours during seedling and vegetative states and then slightly fewer light-hours during the fruiting stage.

• Most research points to ~16-18 hours of light per day for seedling/vegetative and ~12-14 hours during fruiting.

The most important takeaway here is when we calculate the DLI that we want to give our plants, we need to make sure we use the number of hours above and not 24 hours as our light will not be on 24/7.

Calculations and Light Recommendations

Converting between PPFD (from our grow light) and DLI (amount of daily light energy our plants require) is relatively straightforward. There are 1,000,000 micro moles in 1 mole and 3600 seconds in 1 hour. Assuming our light is on a 16hr-on/ 8hr-off schedule and using the centre value in the 12" PPFD map above of 800 micro moles per square meter per second, we get the following DLI:

800 / 1,000,000 = 0.0008 moles per square meter per second
x 3600 seconds = 2.88 moles per square meter per hour
x16 hours = 46.08 moles per square meter per day

This is more than enough but this is also best case scenario - we're using the centre area with the highest output and with the light only 12" above the plants. If we work backwards to figure out the minimum PPFD we need from our light, based on the recommended minimum DLI of 20 moles per square meter per day:

20 x 1,000,000 = 20,000,000 micro moles per square meter per day
/ 16 hours of light on per day = 1,250,000 micro moles per square meter per hour
/ 3600 seconds ~ 350 micro moles per square meter per second.

So, we need a minimum of 350 in our light PPFD maps to grow our plants in their vegetative state and get them ready to transplant. Side note: for growing plants through fruiting, we want ~500 micro moles per square meter per second.

One of the biggest mistakes I see people make (and one I made initially as well) is not considering that different plants that were planted at different times are going to grow at different rates and some will be much taller than others. If you are a home gardener then you are likely not growing in a commercial environment where you a have a shelf of one crop that all germinate and grow at the same time/pace. You aren't going to be able to keep your light exactly 12" above all your different plants all the time. If your tomato plants are 6" taller than your pepper plants (very likely) and you place your light 12" above your tomatoes, the light is now 18" above your peppers. As we saw above, this makes a big difference. Therefore, you need some buffer. My goal is to have enough light, even at the corners, to provide at least 350 μmol/m²/s to my plants from 18" (preferably 24") above.

Now that I've explained my methodology I will go over some lights I recommend and some I specifically don't recommend. My recommendations are based on the assumption that you live in the northern hemisphere and have a shorter-than-ideal growing season, so your goal is to grow indoors for ~4-8 weeks before transplanting outside when the weather is warm enough.

I don't recommend the clip on wand/bendy style of LED grow lights, AKA:

None of these provide a PPFD map showing light output for obvious reasons. This is the first red flag of any grow light. They have nowhere near enough light to produce successful transplants - even when these are so close to your plants that you risk the heat burning their leaves. For most of these lights the PPFD is not even 200 when the light is basically touching the plant. At 12" you are lucky to get 100 and above that you are lucky to get 50. Totally useless beyond helping with seed germination and maybe supplementing small indoor house plants where they just sit right above them 24/7. Don't get conned by the product images on amazon showing utterly superfluous details about lumen output and the number/color of the LEDS. This is just there to make you think they actually put some thought into these lights.

I don't recommend T5/T8 "shop light" style LED grow lights, AKA:

I often see well-known youtubers recommending these while making the point that you don't have to spend a lot on grow lights. They hold one up and go on about how it was only $20 on sale at Home Depot - with the implication that you only need to spend $20 to grow seedlings indoors. Then they pan over to their grow shelf where they have at least 4 of them on one shelf sitting literally right on top of their seedling trays.

These lights are less useless than the clip-on ones above but they are still pretty useless and end up costing more than a proper grow light while being very limiting. Some actually do provide PPFD values though. Here are the PPFD values for one of the most popular versions of these lights (Barrina T5 Grow Lights) currently priced at $50 USD:

So at 7.87" above our plants we would get just over half of the minimum that they need to grow adequately. At 12" above the plants are getting less than half the minimums that we need and at 18-20" it's basically useless. Even worse: these are the values when the plant is directly (i.e lines up vertically) under the light. If your pot is 3" off to the side you wouldn't even get that amount of light energy. The cheapest grow light on the recommended list below is $8 more which is why these lights are a waste of your money and, more importantly, your time.

I recommend any of the following lights for small-ish (2' x 2' and 2' x 4') areas. If you are growing in bigger areas I assume you know all this already and can make your own buying decisions:

1. Viparspectra P1000: Great entry level light for a 2' x 2' or even 3' x 3' (germination/initial seedling) growing area. Currently USD $58.

2. Spider Farmer SF1000: Another great light for a 2' x 2' or even 3' x 3' (germination/initial seedling) growing area. Slightly more efficient LED's than the Viparspectra P1000 above. Currently USD $90 or $76 for the version without a dimmer.

3. Spider Farmer SF2000: I personally have this light and really like it. Stated coverage is 2' x 4' or 3' x 5' (germination/initial seedling) but I think this latter value is a bit of a stretch. I would say max 2' x 5'. Currently USD $180.

4. Viparspectra P2000: Basically a larger version of the P1000. Great light if you need to cover a larger area, or just get two P1000's since they're on sale currently and work out cheaper. Currently USD $128.