LED Watts per Sq. Ft.??? Unanswerable question?
- Thread starter DankDave420
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Rolla J
Well-Known Member
ChaosHunter
Well-Known Member
It all comes down to Photons and how many per watt if I'm not mistaken. 200W of diode LED vs 200W of COB LED at the wall is different. Maybe @robincnn @CobKits @Stephenj37826 can better explain.
mauricem00
Well-Known Member
if you can not afford a high end led than you would be better of with this https://www.ebay.com/itm/T5-HO-Indoor-Grow-Light-2-ft-8-Bulbs-DL828S-Fluorescent-Hydroponic-Fixture-Veg/222107421531?ssPageName=STRK:MEBIDX:IT&_trksid=p2055119.m1438.l2649 or this https://www.ebay.com/itm/400-watt-400w-Dimmable-HPS-MH-Grow-Light-System-Set-Kit/150656047425?_trkparms=aid=555018&algo=PL.SIM&ao=2&asc=41375&meid=640c44e43b6b46569b63aab2a36825f7&pid=100005&rk=3&rkt=6&mehot=pp&sd=282506500516&_trksid=p2047675.c100005.m1851 those cheap LED grow lights are worse than CFLs. you would need a vipraspectra 600 watt to match the radiant power of those 2 CFLs you have. vipraspectra is the only company that I have found who provide independent lab test results for their lights so with other lights you are just guessing. you would need the best LED grow light on the market to match the performance of HPS and CMH or T5s will give you better taste and potency. LEDs may look cool but many of us growers do not want to look cool. I want to look invisible. I don't want anyone to know what I'm growing. and I'm a legal MMJ patient and PU grower.
maximum autism
Member
I don't think that the coolness factor is a selling point outside of the low-end, like the cheap panel that OP linked, and these models are mostly 2010 surplus parts thrown together as a sort of low-info scam.
As far as things being proven for effective growing, I'd say that CFL's and HPS have been proven to be less energy efficient and less cost effective in terms of PPW, which is the reason to make the switch to begin with. You can try to dissuade people from looking into LED's at all, it will fail as the post-2015 stock (including COB's) becomes more widespread. Enjoy your 1970s-tier setup.
mauricem00
Well-Known Member
in the 70's I was growing bag seed with T12 grolux bulbs but HID and fluorescent technology has gotten a lot better since then I am not trying to dissuade anyone from anything. just giving fact based options to low budget growers. the aquarium crowd was the first to use LEDs to grow plants but they have returned to T5s and MH lights for growing coral and plants because they work better. even as structural lighting LEDs are failing. the air force and naval observatory tried them and went back to more conventional lighting because LEDs did not live up to the claims.but I guess you know more than the government and commercial green house and garden center operators. they have tested LEDs and went back to conventional lights. I've done test grows with LEDs and prefer other forms of lighting for taste and potency.
CobKits
Well-Known Member
ALL lighting should be measured in PAR (gross light output - umols/s) or PPFD over an area (umols/s/m2)
you are kinda correct that it is "unanswerable" if the efficiency of the fiture is not known. fixtures like the one you posted NEVER list efficiency because in almost all cases it is no better than the HPS it is designed to replace
so there are two parts to your question:
1. how much light do i need?
2. how can i tell how much my light provides?
A:
1. light requirements vary by growth stage, plant health and to an extent strain. you can be as low as 100 umol/s/m2 ppfd for seedlings, 250 in veg, 600-900 for flowering (or up to 1500 ppfd in a super dialed super vigorous garden with CO2 supplementation
2. so its pretty easy to convert ppfd to target watts/SF if you know the efficiency of your fixture. you can divide target PPFD by 45 to get PAR W/SF. so if you are targeting 900 ppfd (this would be considered strong lighting by most growers in flowering), divide by 45 and you need 20 PAR W/SF
so what is a PAR W? that is actual usable light on your plants. if you buy one of the elcheapo lights like lsited at the top of page 2, thats probably going to be around 30% efficient, so to get 900 ppfd aka 20 PAR W/SF you divide 20 by 0.3 and find you need 66 wall watts of LED
if you spent good money on a real fixture (any of the multitude of systems you could build around current offerings from citizen/cree/luminus/bridgelux, or any of the board or strip designs featuring samsung of bridgelux chips, and ran them at a low current, say 30-50% of their max nameplate current), you could have a fixture thats approaching 60% efficiency. 55% is attainable
so in that case 20 PAR W/ 0.55 = 36 wall watts/SF
quite a difference from 66W/SF, eh? both are producing the same amount of light to your plants. the good light is throwing 16W/SF of waste heat into the room, the crappy fixture is throwing 46W/SF of waste heat into the room!
you get what you pay for....
CobKits
Well-Known Member
that is an erroneous assumption. there is still lots of bullshit lighting out there and the best LEDs are literally twice as efficient as the worst
CobKits
Well-Known Member
search "mccree absorption" on this site. you will find that while green is less absorbed it still is up to 80% as absorbed as reds and blues, and has important plant response effects. which is partially why everybody who moved from blurples to white LEDs saw great results (apart from the fact that the white light is more efficient
Thanks, I did buy a 600w HPS which was overkill and produced as much heat as the core of the sun. I'll look into a 200w version. I only need it for one plant, continuously throughout the year.
GreenLogician
Well-Known Member
The place I bought my cxb rig gives quite a lot of details, but all for the thing running on full power.
I'm wondering if I can figure out the efficiency when I've got it dimmed down, and then what's the ideal power level for my 2.6x2.6 flower tent (80cm)
https://pdgrow.en.alibaba.com/product/60484689669-803344651/Top_quality_netherlands_led_grow_light_cxb3590_x6_led_grow_light.html?spm=a2700.8304367.prewdfa4cf.5.5af4e5ffE4iApT
I'm wondering if I can figure out the efficiency when I've got it dimmed down, and then what's the ideal power level for my 2.6x2.6 flower tent (80cm)
https://pdgrow.en.alibaba.com/product/60484689669-803344651/Top_quality_netherlands_led_grow_light_cxb3590_x6_led_grow_light.html?spm=a2700.8304367.prewdfa4cf.5.5af4e5ffE4iApT
ChaosHunter
Well-Known Member
I'm not a numbers or charts guy. I run at 100w in early veg to the start of flower. 150w for early flower and 175w from mid flower until Finnish. This is in a 2x2.5 tent 5sq ft. My Light has dimming to achieve this. At max 175w divided by 5 puts me at 35w per sq ft.
The ball park COB is you need 35w per sq ft for flower
GreenLogician
Well-Known Member
Cool, thanks ChaosHunter 
Do you have 6 cobs on your unit?
Since I have 6, if you had 4 would that mean mine would run at a significantly lower wattage per cob for dimming to the same total unit wattage, therefore more efficiency and I should undercut your numbers a bit?
Do you have 6 cobs on your unit?
Since I have 6, if you had 4 would that mean mine would run at a significantly lower wattage per cob for dimming to the same total unit wattage, therefore more efficiency and I should undercut your numbers a bit?
ChaosHunter
Well-Known Member
I was one of the first to start growing with Quantum boards when they were released last year. I'm running two 304sCool, thanks ChaosHunter
Do you have 6 cobs on your unit?
Since I have 6, if you had 4 would that mean mine would run at a significantly lower wattage per cob for dimming to the same total unit wattage, therefore more efficiency and I should undercut your numbers a bit?
Chip Green
Well-Known Member
My original 2x2 panels of Bridgelux EB series builds were based on 50w/sqft, Ive spread those collections out on a few panels to the 30w/sqft range, and still achieve satisfactory LUX readings.
Chip Green
Well-Known Member
Before the leap to LED, we had to buy a lamp and build the space around it. Now we can choose a space, and build a "lamp" to fit the space....
What times we live in!!!!
What times we live in!!!!
ChaosHunter
Well-Known Member
We used to take street lights and modify them. Light pole security lights were used and modified for smaller grows. This was 25 years ago.
mauricem00
Well-Known Member
if par is so important than why do major manufacturers and lighting engineers use radiant power and spectrum to compare lights? PPF, and PPFD is just as useless as lumens for determining how well a light will grow plants.atleast lumens is useful for designing structural and area light but nothing in nature follows the PPF curve except silicon and CDS light sensors.vipraspectra is one of the few companies that post independent test data showing radiant power and those test results show a radiant efficiency of about 14%. the best white LEDs can achieve 47% radiant efficiency but only a very small amount of the light they produce fall in 3 of the 4 chlorophyll absorption peaks ( 434,465, 630,670nm). LED makers have always focused on hitting these peaks which is why top LEDs use mono's with a few white leds to provide green light. since the makers of LED grow lights target cannabis growers with one claiming to have a cannabis specific spectrum we are likely to see more white LED grow lights in response to forums like this