Optimum lux at top of canopy - Veg & flower?

[jimmyclone]

just wondering if anyone knows the optimum amount of lux wanted at the canopy level.. During veg and flower..
Thanx in advance

Sent from my SM-G900W8 using 420 Magazine Mobile App

 

[TheFertilizer]

Well my light meter that's meant to be used outdoors tops out at 2000 lux...

 

[jimmyclone]

Im between 20,000-40,000 lux at the different hieghts of my plants.. Thays with an app on my phone though, dont know how accurate that is..

Sent from my SM-G900W8 using 420 Magazine Mobile App

 

[Fuzzy Duck]

So many different measurements of light to work with & no really industrial standard either...


Lux is that not some thing to do with lumen's ? might want to check that out ! but lumen's is just light seen by the human eye mainly yellow/green spectrum it doesn't have much relation to growing tho. It is just brightness.


So you may need to turn your attention to PAR/UMOL where 700 par/umol with most plants will thrive under & peaks out at 1100 par/umol, some bulb brands display this on their own sites & another thing to check out.

Another area to cover is light spectrum & intensity in some areas mainly red for flowering & blue for veg it is pretty standard ye, you may be able to find some charts which show this the bigger the better but don't down play par/umol on bulb size either ! Then their is photo A & B what ever i can not recall at the mo... some thing to do with light spectrum peaks/intensity for growth & flowering more charts to ponder to over.


Then ya have to work out the square law of light effect, ye more home work & head scatching





It is not about brightness !

 

[TheFertilizer]

Well I thought about this a little more after realizing 2000 sounded really low.

Lux is a measure of lumens over a surface area, in this instance a meter squared. That's actually a really great coincidence, since a lot of people work with tents that are 4x4 or some derivative so it makes the conversion of floor space into meters quite handy. In your journal you say you work with an 8x8 floor space, so that's about 2 square meters, give or take.

The issue is that this is a measurement that's more of a mathematical computation, and when we have devices like light meters they need to be calibrated. Most cell phone application lux meters are not properly calibrated. You can buy digital ones that are, but they're more often used for photography, and so when you see them in the thousands of lux range that's a little more appropriate for how bright your bulb is since it's akin to the type of lighting used in photography in terms of brightness.

The meter I am talking about is a cheap combination pH/moisture/light meter they sell at gardening stores and such for five bucks, and I'll reveal why it only goes up to 2000 in a second but first...

Lumen output of a 1k watt HID = ~100,000

Over two feet, due to the inverse square law, that output is diminished by its squared amount with each foot. In other words... 100,000 at the bulb becomes 50,000 1 feet away from the bulb, and 25,000 2 feet away from the bulb. The 12-24" range quoted as most optimal. So, since 1 lux = 1 lumens over one square meter, and your tent is 2 square meters, you'd divide that 50,000-25,000 figure by 2 so you should be more like 13,500-25,000 lux at the canopy.

What I forgot is that a lot of these meters will display the reading as a factor of 10, so you basically read them as *rating*x10. That tracks, because I know from memory that full day light is about 25,000 lux, and the brightest day recorded in Hawaii under direct sunlight was 50,000 lux. So this outdoor meter actually tops at 2000x10 lux.

An easy way to calibrate, is to just go outside with it and see what the lux rating is at a spot that gets a lot of healthy sunlight. Then you can compare that figure to what you get under your light. I am guessing it will be about even. You can also buy a cheap digital lux meter for under 20 bucks.

Fuzzy Duck is right that lux isn't really a measure of light in any way, it's a measure of how bright light appears to the human eye. That can still be helpful though, because if you're working with something you know is a quality light source then the lux simply tells you how much of that light is making it to what areas. With that you can deduce things such as hotspots under your reflector, or if there's enough light to low leaves or to defoliate them, etc. That being said, a lux meter doesn't care if it's measuring sunlight or greenlight, all it measures is how bright that light is. Even saying it measures the quantity of light is a little incorrect, but it's a good way to grasp how to use it to your advantage.

I'll give you an example... I use a 400w HID setup, and an air-cooled hood. That's less than half the lumen output as your bulb, but I also grow using half the floor space. My lux rating is still able to get over 25,000 at my canopy because I am able to reduce the light to less than 12" with little heat, and I know I am not risking bleaching my plants with too much light either. So I don't have to rely as much on the "rule of thumb" suggestion of 12-24 inches and can bring my light down very close to achieve similar output. Now of course it wouldn't do the same over a similar floor space, but my point is that when so many growers use different equipment, then the suggestions of how to use that equipment aren't going to be relevant to every situation, so being able to measure for yourself how much light output you have, and where, is pretty advantageous. If I kept my light 24" above my canopy I would be halving my light output with very little reason.

Just to build on this... My hood stays so cool I can literally have it right on top of a bud, and as long as I have fans going, it doesn't get too hot. A little warm, but practically speaking I could have it probably within 6". BUT that doesn't do me any good because my reflector needs a bit of distance to reflect the light most optimally. If I go and measure the lux on one of my plants that's in the corner with the hood at 6" above the canopy, it will be way lower than if I raise the hood up a little bit more to 14". So you can get a sense for how and where your reflector is sending the light as well. I have actually found that 16-18 inches gives me the best balance between equal distribution over my floor space and highest light output.

Sooo yeah tl;dr... 25,000 lux is similar to full daylight in terms of brightness, but lux cannot measure any characteristics of light itself, it's only valuable use is troubleshooting and optimizing light distribution.

 

[jimmyclone]

thanks alot guys, great info. Im an electrician by trade so lighting and all the equations i have done in first year, long time ago, haha.. Before i started most threads u read were for led. Never really thought about the hight of my hid light. I definitely had the light to close when the girls were babies, that with some low and high temp swings stunted some on the girls. I have mine about 20-24 inches above the biggest 2 and was reading 50,000 lux. About 25,000 out on the smaller ones around the side. I was just really curious if there was a sweet spot that u wanted your plants to be at.. I haven't had any bleaching of the plants so i guess im not to low. And there's a bigger one thats on the outside that is budding just as well if not better than the 2 big ones directly underneath the light. I usually try to turn them a 1/4 turn a day and rotate there position once a week if possible. I understand the par deal but i think par meters are pretty expensive. Also there under hps now so i know there getting the spectrum that they need. I guess if i dont see any bleaching that they should be ok. Some of the corners of the serrated leaves were turned up and i thought mabe they were getting cooked under the light. Heat was only a problem for me at the beginning, as it is getting cold here now. I actually have had to reduce the time of the extraction fan because it is pulling in to much cold air. I took my cool hood glass off because i need the heat that the light provides. I was looking hard at leds, but my heater would be running most of the time to keep the temps up and i dont think i would save anything on the electric bill. I also got 2 free hps bulbs from work so i got the next little while covered for replacements. Thanks for all the info guys.. Really appreciate it.

 

[Williamhuitt1]

Im between 20,000-40,000 lux at the different hieghts of my plants.. Thays with an app on my phone though, dont know how accurate that is..

Sent from my SM-G900W8 using 420 Magazine Mobile App

I use a lux app on my phone..I was wondering the same as you,,"Is my phone accurate." What I've found is that the phone sensors are very accurate..On the better phones at least..Mine is a Samsung S10e..Hope this helps

 

[Apoc]

Short answer,
35-45k lux veg
45-55k flower

At the upper limits you may need cal/mag to keep from burning the plant.

 

[bluter]

ppfd is really the parameter that counts

edit : dammit i answered a 4 yr old thread lol

 

[Timhomegrow]

This has floated as round the forums for a while. My last grow they were at 58,000-60,000 and started foxtailing a little bit. I would think 55,000 may be the limit.....although this graph shows otherwise. Perhaps my last strain was prone to foxtailing and couldnt handle the elevated light intensity.

 

[Apoc]

This has floated as round the forums for a while. My last grow they were at 58,000-60,000 and started foxtailing a little bit. I would think 55,000 may be the limit.....although this graph shows otherwise. Perhaps my last strain was prone to foxtailing and couldnt handle the elevated light intensity.

The upper Lux limit is 55k and if you stretch to 60k you have to cal/mag heavy and even that may not do it.

 

[Ksouth1]

I bought an LED full spectrum light and it started bleaching my big bud plants in veg with a lux reading of 25,000 at the top of the canopy. I always add 2 ml of cal mag per gallon. Can anyone tell me why that is?

 

[Apoc]

I bought an LED full spectrum light and it started bleaching my big bud plants in veg with a lux reading of 25,000 at the top of the canopy. I always add 2 ml of cal mag per gallon. Can anyone tell me why that is?

The light is probably to close.

Pictures with white light and light specifications would help.

 

[Ksouth1]

The light is probably to close.

Pictures with white light and light specifications would help.

It draws 240 watts from the wall. Has red, blue and white 3500k diodes. I moved it up 6 inches from where it was previously and have not had any further issues. Just want to be able to maximize the growth rate. Thank you very much for your time.

 

[Aheadoffyou]

It draws 240 watts from the wall. Has red, blue and white 3500k diodes. I moved it up 6 inches from where it was previously and have not had any further issues. Just want to be able to maximize the growth rate. Thank you very much for your time.

If you grow with led lights Then you need a PAR meter not a LUX meter.