LED & HPS 600 Combination

[BuzzDaddy]

Happy Day Fellow Growers,
I have a question for ya'll.
I'm about 1 Month into flowering my ladies and I was wondering if I could add a cheap 300 watt LED (which i got a crazy good deal on, the only reason i have it), with my 600 watt hps light and get some positive results? Or would I just be using electricity for nothing? Pics of my girls are attached.

 

[Scientific]

The answer to the question, "Would more light be better?" seems always to be "yes." A $16 lux meter from Amazon would tell you the answer (though it won't be any good for an LED light).

You want about 50,000 lux for flowering. If you're not getting that from you HPS, then more light is an option...

 

[BuzzDaddy]

Hey there Scientific, thanks for the response. I will purchase a luxmeter but in the mean time, I downloaded a lux meter app from my phone and tested this morning after receiving your message. If I understand correctly the higher the number the better The Sweet Spot? Whereas directly under my HPS light the numbers were well over 50,000 but when I moved it to the right or the left the numbers decrease. So does that mean along the edges of my grow area where the Lux meter detected a lower number I need more light?

 

[Scientific]

Yeah BD, that's the advantage of getting actual numbers: you can see how much the light falls of away from the focus of the beam and with distance (and it falls off a lot).

It's a fussy, tedious process, but you can really optimize your lighting by taking measurements. If you want to be really exacting, you can draw a grid of your grow space and write down the lux levels at each place on the grid. Typically you have one bright spot and everything else is a lot dimmer.
That is one actual advantage of growing under CFLs and/or household LED light bulbs: although you need ten of them to light your grow, you can place them so you get more even illumination.

If you go out and look, you can find lux levels for various situations from noon on a sunny day (about 100,000+ lux) to moonlight (about 0.1 lux).

Here's something really important to consider using a reflected light meter like the one you're using. (This applies to cameras as well.) The meter is calibrated for 18% reflected light. That is, it assumes that it's looking at soft, neutral gray. (You can even buy a "gray card" at a photo shop.) If you point the meter at something that's more reflective (e.g. snow) it will read a lot higher. If you point it at something that's dark, lower.
(There are websites that tell you how to make your own gray card. Here's the Wikipedia info.)

An actual lux meter doesn't have that problem because it measures the actual light falling on a little white dome, not reflected light.

Using a lux meter on my iPhone I get the following readings at my window on a rainy day:
About 18% gray (an Excel table printed on my laser printer that is soft gray): 548 lux
Same piece of paper as the Excel table, but the white part: 940 lux
Using my lux meter: 740 lux

The take-home message is that if you want to get actual, quantitative readings, it's best to use a gray card of facsimile thereof, and a dedicated lux meter is better.

If you just want relative readings, assuming that you're looking at the same thing (green leaves here, green leaves there), you can see that one is twice as bright as the other, or whatever. My point is, if you compare green leaves with the aluminized mylar of your tent, your reading will be junk data.

Oh, and again, lux meters are not calibrated to work with the "blurple" light from LED grow lights (but you can take relative readings).

 

[BuzzDaddy]

Thanks Scientific. So what I hear you saying is, purchase a luxmeter and create a proper blue print of my grow closet and then determine from the readings of the blueprint of the area, then arrange plants accordingly?
I'm also thinking about putting my 2 smaller girls in the 36"x36"x63" tent and running the 300w led light instead of adding the led light to the hps light in the closet and see what results I get.
I've researched alot about LEDs and get the notion that LEDs are not as effective as hps lighting? This is just my 2nd grow by the way. I know I still have so much more to learn but you have added to that knowledge and therefore I'm appreciative.

 

[Scientific]

Mapping the fight intensity in your grow room is getting pretty fussy for most people, but knowledge is power! And a light meter will give you more objective, accurate, quantitative info than "eyeballing it."

My understanding is the HPS and MH still have more "penetrating power" than LEDs, but that LEDs are coming up fast. My guess is that LED technology will completely supplant bulbs within a few years.

 

[TorturedSoul]

lux meters are not calibrated to work with the "blurple" light from LED grow lights (but you can take relative readings).

It's not just that. It measures based on lumen - and that's heavily weighted towards the frequencies that the human eye can best perceive. IOW, a lux meter gives preference to wavelengths that aren't the best for growing plants. You could, therefore, conceivably get much higher readings from a light source that is actually a much poorer performer (in the grow room) than another one.