Are Cheap Grow Lights Bright Enough To Grow Tomato Seedlings?

Are cheap grow lights any good for the home-grower looking to extend their season and starting their tomato seedlings indoors? If you live in a cold climate or if you just want to get an earlier harvest, then starting tomato seeds early is a necessary step. In this video, I investigate if cheap LED grow lights that you can buy on Amazon are powerful enough to stop tomato seedlings from going leggy and to produce healthy plants.
To find out, I’ll run my own experiment and grow six tomato varieties under different light intensities and share my own data on how much light tomato plants need, determine how close you need to place your tomato seedlings to the lights to keep your tomato plants healthy and discover which varieties grow best under artificial lights.
You can read the written version of this video and see the results for yourself at www.alexgrowsfood.com/post/ar...
AD - To make this video, I used the following equipment and varieties:
💡 LED Grow Lights (Set of 4): amzn.to/48TZLxl
(But the newer model might be of interest): amzn.to/48XyLgl
📥 My (Modular) Flat-pack Shelves: amzn.to/3U4MC0d
🔥 You might also want some heat mats to help them along: amzn.to/3tQCttv
🌍 I always use this organic seed compost: amzn.to/43Uu5oP
🥥 I used this organic coir: amzn.to/3S0PSXL
🌋 And perlite too: amzn.to/3vFnhQk
🟡 Sungold: amzn.to/47FmwnL
🔴 Red Cherry: amzn.to/3O6z8x3
🔵 Black Cherry: amzn.to/4aXK7mr
🟢 Tigerella: amzn.to/4b4iU1B
⚪ Costoluto: amzn.to/47UG3Rn
🟣 Roma: amzn.to/3S19pr9
Other equipment should also work (with a few caveats) if you follow the recommendations in the video. And as an Amazon Associate I earn from qualifying purchases. This doesn't affect the price you pay but helps support the channel. It doesn't sway my content --- with the exception of my love of the Sungold tomato, I'm just sharing hard data here.
One thing I didn't talk about was the quality of the light spectrum or colour temperature - I had to cut it. These LEDs claim to be full spectrum but they produce that from two (or three) LED colours. Recreating perfect daylight spectrum is also difficult (expensive) so there's a good chance this isn't accurate --- but it doesn't have to be! I also didn't talk about how many seeds I sowed (the Roma tomatoes did double-up more than other varieties because you get 75 per pack rather than a dozen) which may have had an effect as they got bigger.
We covered a lot of ground in this video. Let me know in the comments if you have any questions at all about my experimental setup or methods or anything else I forgot to mention (or likely cut out).
And apologies for those not using metric. I did a last-minute render to add Fahrenheit but there are 100 centimetres in a metre and like 3 and a bit feet in a metre or something...
There were also a lot of technical issues during filming. More than I've ever experienced - it turns out they are like buses. The radio microphones dropped out a lot in the first half of the video, including during the re-shoots, so I had to buy new equipment and re-record the audio and try to lip-sync with myself. It sort of worked but there a couple of places where it didn't. Apologies if it looks weird (the second half is grand though).
Otherwise I hope you enjoyed this one and, as always, Happy Gardening!
Follow or contact me via
📸 Instagram: / alex.grows.food
🌐 Website: www.alexgrowsfood.com/
Thanks for reading this far! To let KZbin show you more of my videos about growing food at home, press the like button or click this button to subscribe: / @alexgrowsfood
I get most of my music and sound effects from Epidemic Sound and it has transformed how I approach making videos. If you want to try your hand at this KZbin thing, there's a 7-day free trial at: share.epidemicsound.com/76meao and I've got a playlist of some of my favourites available at: share.epidemicsound.com/76mea...
Credit to the following artists courtesy of Epidemic Sound:
Binkley / 'Lovely Ghost'
Victor Lundberg / 'Down By The Creek'
Vincent Vega / 'Tomorrow'
Par / 'You Are My Little Sun'
Raymond Grouse / 'Toss Me The Tomatoes'
Victor Lundberg / 'Tell Me I Should Have Known'
and
Grieg / 'Morning Mood' / KZbin Audio Library
0:00 - Starting Tomato Seeds Early Means You'll Need Grow Lights
0:32 - The Equipment and How I'm Going To Test It
1:18 - Sowing Tomato Seeds
2:48 - Setting Up The Grow Lights & How To Create Different Lighting Conditions
4:42 - Getting Tomato Seeds To Germinate Faster
6:15 - Timelapse of Tomato Seeds Germinating
6:27 - Which Tomato Varieties Performed Best Under Grow Lights?
7:39 - Can You Grow Tomato Seedlings Under Grow Lights?
#growyourownfood #growlights #tomatoplants

[@alexgrowsfood]

Let me know if you have questions about growing tomatoes from seed under lights or about the experimental setup. It took me a long time to film (did you see my hair grow out?) and I definitely skipped over things. It also looks like the brand have updated their grow lights, so if you want to get the closest model I'd get these amzn.to/3U5ivFS (ad) but a similar power delivering full spectrum should work

[@worstworkshop]

Watching your videos always makes me feel better about everything. Thanks.

[@alexgrowsfood]

Thank you!!! Not sure what to say to this. It's probably the plants... 😉

[@avendesora222]

Wow, great video with great data collection! This should have thousands more views! KZbin suggested it to me, so it’s on the right track I’d say!

[@alexgrowsfood]

Thank you so much!!! My videos are a lot of work and normally quite slow out the gate but the stats look _really_ good. It's just started to get pushed out so fingers crossed it keeps going!

[@pmcgowan742]

This was amazing. I loved the Timelapse shot of the seedlings growing 👏👏👏

[@alexgrowsfood]

Thanks Peter, I appreciate that. I was tempted to upload the full time-lapse at 4x speed rather than 20x, if that would be interesting let me know and I'll try and figure out the best way to do it

[@andreagilpin5788]

Thanks for another great video Alex!

[@alexgrowsfood]

My pleasure, Andrea. Glad you enjoyed it!

[@stanleymersino943]

This is such a good video! Tons of great info! Instant subscribe!

[@alexgrowsfood]

Thank you so much, Stanley!!! This one took a few weeks to prep & edit so I really appreciate your message

[@AlexBraunton]

Great video Alex, thank you for sharing the results

[@alexgrowsfood]

Thank you!!! No worries, it was fun getting my science hat on again

[@marksminis]

Excellent info Alex! You’ve saved us the work of figuring out which variety and the distance, that saves us a lot of effort!

[@alexgrowsfood]

Thanks Mark! I definitely panic bought those extra lights that clip on the front --- turns out it isn't necessary after all!

[@sw6579]

This cleared up all of my tomato starting confusion. Excellent video. Thanks!

[@alexgrowsfood]

Glad it was helpful! It was meant to be a grow lights video but really it was an A-Z on starting tomatoes

[@rachel8006]

What a well done video! I learned so much!!! Thank you 🙏 i subscribed!!!

[@alexgrowsfood]

Thank you, Rachel! Really glad you liked it!

[@JBNat]

Incredibly detailed video Alex, mind boggling how much effort has gone into it. I almost gasped when you had that stem measuring tool out 😂 I'd thought about doing a similar video on this topic but there's no way it would have been as good as this!

[@alexgrowsfood]

Thanks JB! Yeah this one took about a month to plan, film & edit (although I re-shot most if it two or three times due to microphone issues & had to dub in places). And I had to re-learn how to plot graphs in python too... Tbh I missed so much that you probably could make another video and not even duplicate anything - I didn't even talk about spectrum or what colour light promotes what kind of growth or try other seedlings or other lights. Definitely a really interesting topic. Would love to do more or test a light from a better known brand but maybe I'll save that until next Winter.

[@monikap8585]

Great video, thank you 🙂

[@alexgrowsfood]

Thank you so much. You're very welcome!

[@manuelferreira1363]

Thank you for a fabulous instruction. Your video presentation marks your skill as a producer/director/editor too. I subscribed naturally.

[@alexgrowsfood]

Thank you Manuel!

[@NickkkOnTube]

great experiment, great presentation! Thank you sir!

[@alexgrowsfood]

No worries, glad you liked it!

[@hopskotia]

Good stuff! Using lumens is a poor method of measuring light for plants, opting for PPFD or PAR when you can...although it's often the best you have with a phone camera based app. The more Important information is what spectrum that specific light puts out and how strongly it puts it out. This WILL vary greatly between lamps. That said, Germination rate and strength of your seedling will have less to do with the light and more with soil and humidity conditions they are terminated in. A warm humid, even dark, environment will germinate very well. Photosynthesis doesn't make a large part of energy until they start growing true leaves.The plants will use the light to determine "up", but will get most of its needs from the seed, and air as it works to grow roots. A slight breeze would also strengthen seedling stems as they grow to counteract the movement. Thanks for the video! 🤘

[@alexgrowsfood]

Thank you! You're right on everything. I have a physics background and did a PhD in modelling organic solar cells and it was a tough choice deciding how in-depth to go on this one. I was already a bit worried I spent too long talking about intensity and the shape of the light and was taking too long editing the video too. I cut out a whole section about light spectrum & colour temperature but didn't realise I also cut out the other bit about these lights claiming to be full-spectrum. I also didn't properly explain why DLI over lumens was important (for anyone reading this, it's about what part of the available light is photosynthetically useful - which requires information about the bulb/light spectrum and goes into PAR. DLI is proportional to PAR). In the app I selected full spectrum but it's unlikely to be truly full spectrum at this price as accurate daylight can be expensive to create. I also didn't calibrate the app, I just did a quick 'makes sense' test. I also didn't put error bars on my graph (which is perhaps the most unforgivable). And using a fan is a top tip - I relied on the strength of the wind coming in from around the window frame but a fan would do a better, more reliable job. Thanks for the comment, it's really useful information for anyone who wants to know a little more about 'the why' behind some of this

[@hopskotia]

@@alexgrowsfood the things we must sacrifice to make consumable content. 😉 It's good! I am a light/lamp nerd, so I probably am not the typical audience! I did enjoy seeing the approach and the results! Heating mats would have been great, but as you pointed out, pretty pricy! It would probably be more efficient to have a small tent for your propagation as the heat from the lamps alone would typically be enough to insulate them from your household temps. Thanks again for the content!

[@SloggieBear]

Very helpful

[@alexgrowsfood]

Thank you, glad it helped!

[@chrislilly1463]

Great video Alex! I'm going to be embarking on a similar journey in a couple months. I'm still in true winter here (-33c last 4 days), so I won't be starting anything just yet. My season is basically June 1 to August 30th (90 days which has a rainy June, hail filled July and finishing of with a normally super hot August which often ends in a dramatic killing frost) After August any extra time is a bonus. Growing indoors at least to start is a big must for me if I want to grow anything interesting. My last frost date is close to June1 so I have some time yet. Life in the Great White North eh! (I threw the eh in there, we don't really say it often). lol Cheers form Calgary.

[@alexgrowsfood]

Just trying to comprehend -33c for a second.... Definitely start indoors but you could probably provide enough light for some adult plants at levels not _that much_ brighter than these. Try and google the DLI number for each type but tomatoes at five centimetres would likely be about double the brightness. You could get better lights than these and double up with them too and top the soil with coir or something that doesn't mould. You probably know all this already and grow for a few months indoors to start.... Do you do a lot of container gardening with things like peppers and finish them indoors or mostly just stick to leafier/quicker growing crops?

[@TMCRok]

Thank you for your efforts! You did all of the work I've been wanting to do for me! Even the graph! Fantastic! What software did you use if you don't mind me asking?

[@alexgrowsfood]

Thank you! Honestly, there's a lot more that could be tested and I didn't even talk about spectrum. I made the plots in Python using the matplotlib library. The lines are an exponential decay (plus a constant) fit to each variety using scipy (I think scipy.curve_fit but it could be scipy.optimize) - not sure if it was best choice of model, especially at low DLI, but I think suitable for finding the flat region

[@flo2col127]

I bought 3, four foot, LEDShop lights. Removed the diffusers. My lights work great.

[@alexgrowsfood]

Nice! They sound big and powerful too if they come with a diffuser. Glad they're working out for you.

[@TheGeek365]

Great video Alex, loads of information and good tips. This would also apply to other types of plants as well such as peppers, cucumbers, etc. I'd also like to know which tea you used, I've tried chamomile tea for peppers before but didn't notice that it helped much with germination. That or I didn't soak it long enough as I only did a 4 hour soak.

[@alexgrowsfood]

I expect so although I guess the exact light levels might be different for each plant. I've sown some squash and it already looks like it wants *a lot* of light. But that sounds like a video for next year.... I used Twinnings English Breakfast. It's been stale for about two or three years now. I think the blend they sell outside the UK tastes better so I presume it works better on seeds too! I read somewhere that peppers need a longer soak than tomatoes but I think it depends on the individual seed (for both). 24 hours is probably the sweet spot between moisture absorption and avoiding issues with rotting. I also read that the tannins in the tea help break down the coat chemically - if true that might explain a difference with chamomile, although I suspect the time has a bigger effect. I also think coir is straight-up magic and I wonder if soaking is less important there where you can have higher moisture content in the soil without risking as many of the issues you might get with wet compost.

[@RickysFarmAndHatchery]

My precious....

[@alexgrowsfood]

That would have been a good skit at the start, that's for sure! Wish I'd thought of it...

[@rebekahzone]

Beautiful Information Alex! Thank you so so very much. Do you use black tea for the seeds?

[@alexgrowsfood]

Thanks Rebekah. Definitely black tea. Milk would cause too many issues. I used Twinnings English Breakfast. The tannins in the tea are meant to help break down the seed coat (although I've not verified that). My nan used to make a cup for her and a cup for the plants so it doesn't have to go to waste either.

[@rebekahzone]

That is so cool! Thanks Alex! @@alexgrowsfood

[@alexgrowsfood]

No worries, good luck growing

[@homesteadknowhow]

I just bought eight 48-inch seedling lights from Amazon. I didn't read the entire description and assumed they were the equivalent of the lights I already had. I need around 4,000 lumens at a minimum for each seedling shelf. The new lights are only 600, incredibly dim. Now I need to buy more lights. Currently, I use both LED and fluorescent lights. In my experience, Roma tomatoes always look a bit leggy and light-colored at first. By the way, I love the experiment.

[@alexgrowsfood]

My lights are definitely on the low end - I think it was 2,700 lumen in total emitted from about 120 inches if I recall so about double what you ordered (assuming spread is similar etc) but closer to what you suggest is your minimum. With Amazon you can always return them no questions but if you can get them close to the light and adjust as they grow then you _might_ be able to provide enough light for young seedlings (with all the caveats at the end of the video). You'd have to check though --- the distances would need to be much shorter and you'd have to constantly adjust so it would be a lot of work. Otherwise you could double-up if they were cheap enough! I find the spread isn't quite as much as I'd like at the very small distances so a second set would help and get your shelves up to about the same light intensity. Of course that only works out if they were half as much (I doubt it) and/or if the quality of the light spectrum is better (maybe that explains the dimness?) Yeah, I don't like Roma tomatoes but found it fascinating how they shot up. They slowed down but the widths never caught up with the rest. Obvs you can bury the stems but.... I just wish I had tested more of the other types of tomato --- the seedlings were very different and I wonder if, in general, plum & beefsteak grow taller earlier than cherry tomatoes. I've not grown enough varieties or, more importantly, noted their growing habits to know for sure.

[@roywarriner8441]

Have you tried led shop lights? Amazon has a good selection in 24, 48 and 96" lengths. Imo they are cheaper than and superior to the grow lights sold for house plants or seedlings.

[@homesteadknowhow]

That's basically what I got, but I bought a riduculously dim option. @@roywarriner8441

[@charlenefrench5404]

Great video. I bought one spider grow light and one heating pad. How do I safely transition from that to outdoors?

[@alexgrowsfood]

Great question. It depends what your climate is like but for most annual seedlings in temperate climates you want to harden them off slowly over time so they can acclimatise to outdoor temperatures as well as forces like wind and exposure to the sun. The usual method is to bring them outdoors for an hour or two in the morning and evening but bring them indoors at night and during the brightest part of the day (to avoid the harshest sunlight) and then stretch that out until the plants are out during the entire daylight period --- this usually takes two or three weeks. If you can start in a shaded location before adding direct sun, that can help avoid sun exposure issues too. For warm climate plants like tomatoes and peppers, you'll want to put them somewhere warmer so that the temperature is more than 10-12'C when you harden them off. During the early stages, this is can be done in a greenhouse and then they can go through the hardening off process later in the year when the day time temperatures are higher. The recommended temperature is often quoted as 12'C and letting them experience colder temperatures is meant to stunt growth, but I normally go much earlier (around 7-8'C) especially if they are on concrete or stone and the sun is adding localised warmth. I suspect you could probably add your own wind indoors and bring in enough light, including UV to acclimatise plants indoors in a very controlled way but when the outdoors is right there and it's free, it's normally not worth it. You could use fans now though to make sure your plants grow strong enough roots to stand upright later on. Start gentle - just enough to make them vibrate/shake a little to stimulate that sort of growth. I've probably missed some points, but hopefully enough to get you started. Let me know

[@haidarhakim2265]

Incredible video mate, next time can you make a video about cherry tomatoes diseases & pest prevention

[@alexgrowsfood]

Thank you for the kind words. I'll see what I can do. It won't be any time soon, mind... It'll have to wait until summer. I did make a video about pruning to avoid disease which also points to a video about watering correctly and there's a video on passive pest control which talks a little about interplanting for tomatoes at about the 2 minute mark (it's all chaptered). They should all be available in this playlist: kzbin.info/aero/PLMNjC6h_XSTZ2cfzP1h-QLYvNFiGT8sTo. But it those aren't quite the ticket there should be some good suggestions in the feed for each video

[@locke6531]

👍

[@craftimeei]

Which grow light app do you recommend to use on the phone?

[@alexgrowsfood]

I used Photone. It's on iOS and Android and the default setting is reasonably good (no need to calibrate unless you suspect there is a problem with the readings and have the equipment to do so).

[@stan9682]

what is the name of the app you used to measure the amount of light?

[@alexgrowsfood]

It's called Photone. It should work on Android and Apple and it's free to download (on Android anyway). It might take a bit of time to figure out exactly where the light sensor is but if the phone is in the right spot and the right kind of light is selected in the app settings it should be fairly reasonable. You can calibrate if you have the setup to do that but my understanding is the default Apple settings are pretty good and the android output made sense from some rough measurements

[@stan9682]

@@alexgrowsfood Thank you! I'll probably don't need to calibrate, I'd be using it as a comparative measure mainly.

[@alexgrowsfood]

No worries! That sounds perfect, just make sure it's on the right lighting type setting and you'll be good to go. I don't know how easy it is to reset and go back to factory calibration either so leaving it well alone makes a lot of sense

[@samsheehan5298]

I just started my seedlings they're 7 days in all natural light from the window. They look like they might start to go leggy so I ordered a pack of the lights you used in this video. Does one pack come with two lights and will putting two lights over the seedlings improve growth? I'll be looking to upgrade my lamps once I become a more experienced grower.

[@alexgrowsfood]

Hi Sam. It depends on which link you followed (and if Amazon redirected you - for non-UK stores) but mine (the top link) should give you four lights in one all connected to one timer unit. The second link is two in one and I think there's a two units (four lights) option if I recall. Doubling your lights will help your plants grow. During the early stage you can keep plants further away from the light or you can move further right along my graph and have shorter, leafier plants. And as they get older and need more light, these lights should be able to provide the extra light they need. For adult fruiting plants, I think you'd need something like six lights at 10cm distance but for young plants they should be good for a few tiers of true leaves. Mine only had one top light and one of those weird side/clamp lights I showed after moving the rack upstairs at the start of the video. With that setup mine outgrew the racks before needing more light. I suspect the intensity on the side lamp was similar so two lights is probably all you'll need to get them to planting out size - or, given the time of year, to get them large enough to start hardening off. The main issue is area coverage is small so the number of plants is lower with this setup than the wide area rectangular lamps. This is a long comment and what I'm saying depends on your exact location but I'd consider using outside natural daylight on warm but cloudy days where possible and in the morning and evenings using the window and lights. Window plus lights is a good combination in the early stages though. Recommend you use that app and make sure your intensity is high enough. If you can get to a DLI of 10 mol/msq/day using lamps and the window they *should* be more than fine until the hardening off stage

[@samsheehan5298]

@@alexgrowsfood Thank you that is really helpful. The trouble with my windows is that they have balconies above them so it restricts the amount of light that can come through. On sunny days the plants a good 6-9 direct sunlight. I can then send them over to the other-side of the apartment at around 4/5 where they can get another hour or so of good sunlight. The trouble is that it is cloudy 3 out of 5 days at least currently and I don't think its enough to make them strong. I'd like to experiment with flowering indoors at some point with a stronger light. Would it be expensive to get a tomato plant to flower with a grow light?

[@alexgrowsfood]

No worries. I appreciate the shading issue. I didn't have anything above but I did have an awful garage to the south and east of a kitchen window once so my tomato plant only got early morning light and the rest was completely indirect. It did go leggy (I didn't have grow lights) but it did produce two or three fruits. If I recall correctly, an adult plant needs about 25-30 mol/msq/day so it's definitely achievable (a window and four lights might even be enough in principle). The main issue I can see is that the plants get really tall so you need a space where you can raise the grow light by as much 6-9ft (for indeterminates). Of course, you could always pinch off your plants and keep it small or grow a bush variety, then it's just a question of getting a bright enough light and knowing how the light is emitted (over what area below) to calculate the intensity of light at leaf level and convert to a DLI value to verify that it's sufficiently bright for an adult/fruiting plant. To estimate how much it would cost, you could probably just look at getting a light with 6x (or ideally more) watt rating (not power consumption, we want light emission) than these little lights and compare prices. A handful of plants shouldn't be too expensive - one big light will probably be enough - but scaling it up could get pricey quite fast. You might also want to look at adding wind to make sure the roots get good an anchoring the plant and that the stem can support the fruits it produces (a desk fan on low setting will do the trick). It might also be a good idea to grow cherry tomatoes because they weigh less and you can pull off fruits if it starts getting too heavy.

[@samsheehan5298]

@@alexgrowsfood It's amazing really isn't it even to get a couple of fruits in conditions like that just shows how determined they are! I just actually realized I'm getting sunlight from about 13:30 from my west facing window so I've moved the seedlings over. Hopefully they don't become overly leggy before Sunday when the lights arrive. I'm also sewing chilies, parsley mint, coriander and dill. So far only the Dill and parsley has shown signs of growth. What would you recommend for growing herbs and Chilies successfully?

[@craftimeei]

My LED grow lights might be weakening my tomatos, I dial it to the yellow light with the lowest setting. They are so weak now they are suffering from sunburn by the sunny window indoors. They are taking a long time to recover and there is not enough natural sun and I am not sure if my grow lights are helping them at all. I don't know what else to do.

[@alexgrowsfood]

Sorry I completely missed your comment. I really hope the tomatoes recovered. My instinct is that it's unlikely to be sunburn through a window in April. The main issue with grow lights is that if they aren't bright enough, the plants go leggy and get too tall to support themselves. And what you quite often find is that even on a windowsill this is the case because the window absorbs most of the UV and attenuates some of the light anyway and the window is only facing one direction so the amount of light is too low. For grow lights, because they are much less bright than the sun, the best thing you can do is turn it to the max setting and use the white (natural) light mode (which normally means having all bulbs turned on). The yellow light is lower energy light and there are some chemical processes that require higher energy (blue light) to take place so you want the mix. The best thing you can do would have been to keep the plants at the window (or outside the shade during the daytime, if warm enough) and look at what's causing the discolouration. If they really are going white and bleaching (rather than yellow), then reduce how much windowsill time they get or try and provide some shade to reduce the light intensity. Even a pillow case against the window for the brightest part of the day or move the plants away during that time. But I find this unlikely - usually the problem is too little light. If the leaves are going yellow or brown then it could be all sorts of issues from nutrition to watering and it could be a case of re-potting into new/different/drier soil and letting the pots dry more between watering (or less if you're as slow as I am). If the plants are going purple that could be a nutritional issue too although I find the plants normally survive until they are in the ground and then recover in this last case. Sorry I was so so late and can't be more specific. It might be too late now but maybe this will help next time.

[@highphysics3617]

Wow! This just the information I needed. Where I live is heading for winter, Australia}so growing under lights is what I need to learn. Great presentation,Alex. I want to try Cherry tomatoes,and,Grosse Lise. tme will tell. Thank you for all your hard work in putting this great video together.🥰🦘🦘 🧓

[@alexgrowsfood]

No worries! It took a while but a lot of fun. I'd definitely limit these lights to seedlings and look for something brighter for adult plants. Their requirements increase as they age. If I recall, fruiting tomato plants need something like a DLI of 25-30 mol/cm2/day. I think mine were good for 2 months under this and then they out grew the racks anyway. I might do a follow-up next year (no promises)

[@highphysics3617]

@@alexgrowsfood This whole venture is an experiment for me,as trying to grow summer tomatoes has NEVER worked,yet others can grow them like weeds! Following you has given me a lot of confidence to try again,a completely different way. I have more lights coming this week. My beans are powering away like crazy. Fast broccoli yet to emerge. This is so much fun. Keep itup Alex. You are great to watch

[@highphysics3617]

@@alexgrowsfood Hey Alex,My new light arrived today. It's bigger,and,has a diagram about Photo ,Flux Density Meaurements, ....{what a mouthful🤔🤣 } from 0 cm to 60 cm. The highest is 60 cm 100 mol/ {m2.s} ,and the lowest 0 cm 1200 mol/{m2.s} Is there somewhere in your videos that explains that a little? Awrabest.

[@alexgrowsfood]

Very cool. I very briefly talk about light intensity and distance in one of my diagram sections but I don't think it's going to help here and I don't go into detail much anyway. You've got physics in your account name so I'm going to assume some prior knowledge but flux density looks like a rate per area which is an intensity which is good. It should be a conversion to mol/cm2/day (or the other way around from my number to your light's number if it's easier). The numbers you're quoting look like it's giving you the intensity values for the corresponding distances away from the leaf/top of the plants. That's either giving you the total number of photons per second per area or the PPFD(photosynthetic photon flux density) which is a count of the useful photons per second per area for the plant which you then convert from per second to per day to get the DLI. Getting the PPFD value will depend on the light spectrum of your lights which, hopefully, is daylight and there are equivalent numbers for each light mode. I spent a lot of time reading around the different units and it's definitely worth a look (there is a note about grow lights at the bottom too - although I have a hunch yours is fine) en.wikipedia.org/wiki/Photosynthetically_active_radiation#Units. If I recall daylight spectrum intensity to PPFD is a numerical conversion factor and same again to get to DLI. But once you have the DLI converted to PPFD/Intensity (or vice versa) you should be able to find the point in their scale where the converted value matches a given height (or plot a curve if it's very discrete) and that's where you set your lights to. I would recommend double checking everything with the app (I used photone, set to daylight but set yours to match your lights) or some calibrated meter. I'd recommend using the app to check your conversions because you can swipe between modes. If I recall you should be able to get a pure intensity, a PPFD, a PAR and a DLI. The other way is to go full experimentalist and use the app to try and recreate the measurement at each of the data points in intensity mode and then swipe across to DLI and find the height you want. I did computational physics which is why this is more of a footnote. Google says your numbers are very very bright but it's past my bedtime and I've not checked it's workings so I don't quite want to post them here in case they are wrong - but if they are right you'll want to adjust the brightness setting or to go a little higher. That or it's micro mol / (m2 . s) Let me know if you're still scratching your head in a few days (or if you've already solved it) but once you've got the units and where they come from nailed (and how spectrum and area and exposure time affect each measure), you've basically mastered grow lights.

[@highphysics3617]

@@alexgrowsfood Aha! Brilliant Alex. I will soak all that information into my foggy brain supping on countless cups of tea. Heaps of thanks for the detailed explanation. So far my little plants are exploding with growth,so I must be doing someting right with your guidance.. Completely opposite ends of the world and it's working. Never too old to learn,huh? You are wonderful.🥰🤗🧓🦘