What watt of LED i would need?

A customer has a question or concerns and I hope we can get some opinions on it, thanks.

So i got two plants starting to sprout and was wondering about lighting. Im waiting on a grow tent at the moment so i have no lights right now and really dont want to spend to much on a light im use for a month because my grow tent already comes with one. So was wondering what watt of LED i would need to cover two plants or other possible cheap options i have. The grow tent broke me so im on a really low budget and half tempted to give up on the two but dont want to waste good seeds.

How big is your tent? You need 50 true watts per square foot. So if your tent is 2x4 like mine you need 400 true watts (watts coming from the wall) not what the light manufacturer says the watts are. A 300 watt led might only be 150 true watts. A 2x4 tent would need 2x4 = 8 sq ft x 50 = 400 true watts.


Size of space is important to know but @HJL has given you a good rule of thumb formula to help you figure this out

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What size light comes with your tent? Again, you must determine what the true wattage (wall wattage) is rather than what is referred to as "equivalent watts) which is what most LED manufacturers claim. The true wattage is on the name plate and should be available online.

I agree with the others. It also seems that a good portion of those tent kits that supposedly come with everything you need are generally undersized.


I dont have the tent yet i need to find a light to cover the 2 plants till i get the tent was wondering what i need just to pass 2-4 weeks till the tent comes

What’s your budget? You could use something like this.

Just add 23 watt 5000k cfl’s or 15 watt 5000k LED bulbs.

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If I were you, I’d buy a 300w led light from Amazon that has veg/grow switch on it and uses a 150 actual watts. @dbrn32 is right. These tent setups don’t have enough light included with them. My local grow store has one of those “ready to grow” 4x4 tents and I laugh at it every time I walk in. @HJL is also right. You really need 50 watts sq ft unless you are going to build your own Lights.


On a side note @dbrn32 What would a spectrum graph look like for 7 x 100 watt (16 TW) LED 4000 k bulb with diffuser removed? Is it more blue or red? Would I be better off using my two round UFO LED’s that are 31 True Watts and 57 True watts in my flower tent or the 7 x 23w LED’s mentioned above. I will eventually replace everything with a quantum board but I’m saving $ for that right now. Thanks for your opinion.

Most manufacturers 4000k is going to be a touch heavier in blue than red. I haven’t seen one that isn’t, but you do see some slight variations in phosphor from one manufacturer to the next. Color rendering index will come into play as well. A 90 cri led produces deeper reds than an 80. That being said, the relative intensity in most colored led panels isn’t a lot different than a 4000k. What you’ll see different is where they peak. Your ufo light should use something like 630 and 660nm leds. So you’ll see the peak of red bump in that region on graph, even if the amount of light produced in that range is less than blues. On your 4000k which I’m gonna guess is around 80cri, you’ll see that bump in red around 600nm.

To answer your question, I’m not sure. You’re probably close to the area where it will be a crap shoot. If you’re ufo has a decent amount of 660’s I may guess that it would be slightly better. If it’s mostly 600-30mn leds, higher power will probably produce the best.


A cheap 2 bulb flouresant light will get your seedlings going just keep it close to your plants they give off little heat and can b bought for about $50 at the grow store or you could get a shop light fixture $20 at the Depot and run a cool white and soft white build in them might b a bit cheaper

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Or just four of the 23 real watt CFLs from WalMart would be fine for seedlings. Use a flat white reflector above them and hang them 6 inches over the seedlings. I’ve got some right now with this setup and they are very happy. Those four CFLs will light two square feet just fine.

Obviously, for real growth you need more. LEDs are good. RapidLED has some nice COB kits that just snap together. Home Depot online has some pretty cheap MH+HPS kits.

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