Using Light Efficiently

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Esteemed Member
Cannabis Fan
Completed Grows

In the light calc it states that for the Mars Hydro TS 1000 the best height is 18". Is this due to the design of the light? Do the lenses over the leds cause a focal point 18" below the light? The light intensity maps show that the closer the light fixture is the more PPF.


Second question my grow box is a 3.5' x 3.5' the the light calc says that I need 790 usable PPF I have 968 with  a TSL 2000 and 2 TS 1000s I am about 200 PPF over and if I remove a TS 1000 I will be 60 PPF under or I can lower the output of the lights. The plants don't have any problems but I don't want to waste energy if it's not going to help.

Thanks for your time


Posted : 06/06/2020 6:13 pm
Dr Photon
Member Moderator
Expert Grower
Completed Grows

The design choice for lenses depends on the design of the fixture itself. And can be required to disperse or converge light depending on the size and power of the light source. But the idea is to control light from a fixture to more effectively deliver light to the intended area. The Mars TS series however do not use optical lenses. And simply emit the diodes directly from the diodes themselves. Which is possible because of the large surface area and output capacity. Which more naturally spreads light uniformly. 

The optimal fixture height is a balance between optimal canopy photosynthetic efficiency and reflective losses. Too high and you loose light to divergent and reflective losses. Too low and you loose energy through low photosynthetic efficiency and non photochemical quenching.

Light intensity may appear to get stronger as you get closer. But this is a misconception. It is just the nature of the light source not being able to diverge as much and so energy becomes denser at the central locations. Think of a torch that you shine very close to a wall. Its surface area is small but its density is high over this surface area. Step back however and you can make the surface area larger but the density descreases as it now has to spread over a larger area. But the total amount of energy remains the same when calculated or measured as a whole.

You can see gains going above the optimal light levels. But it becomes a level of diminishing returns. 

Being wrong, is an opportunity for getting things right.
Posted : 06/06/2020 11:06 pm siscoweb liked
New Member
Cannabis Fan

This great information Dr Photon! 

We have been growing (flowering) with HPS for about 12 years. Recently, we decided to upgrade to LED and I am having to learn to adjust our environment to accommodate the LED Fixtures. It has definitely been an intense learning session.

Our last grow, we compared the same strain from the same mothers in two different rooms. One with 6 1000 HPS the other with 6 LED (600w). Our yield under LED was about 1/2 of that under HPS.... this I believe to be due to our lack of experience under LED. Getting the environment right is crucial!

We have been debating whether more plants or less plants produces the best yield in a given grow space environment. The question that comes up is... if you only have so many lights (umols) available, does there become a point where more plants do nothing to improve your yield? 

As an example, PPF is like (to keep it simple) vitamins to plants. If there are only so many umols (vitamins) available to the group receiving them, logic would state that there is only so much yield you can get from a specific amount of umols being given. The Useable PPF Calculator would seem to indicate that this theory is true... Dr Photon... am I on the right track?

In other words if 30 plants produce 11lbs under perfect conditions (approx 6 oz per plant), under 6 lights... would 60 plants only average 3 oz per plant thus still only producing 11lbs?

We appreciate your insight and guidance. 


Posted : 07/10/2020 8:35 am siscoweb liked
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