PWM vs Current Dimming and PPFD dropoff

Hey guys, looking at how I should go about running my new lights from @Grow Lights Australia.

I've got two of the new double units in a 4x4x6 box. So a total of 960w. This is in excess of my current requirements.

I'm working with the PAR maps of their previous lights as they haven't released maps for their new ones (nudge nudge).

I guess my question is, does PPFD decrease linearly with drive current or PWM duty cycle? I'd like to dim them, however I'd like to have a ballpark figure of PPFD at the canopy so I know what I'm working with. I'd prefer to dim them using PWM over current, as my controller can then log the approximate light intensity

maybe this help you a bit...

Dimming LEDs via PWM and CCR APP NOTE (048360) - Lutron

PWM based drivers can provide a very precise output level, since the LEDs are always on at the same current
level.
Changing the operating current linearly, as done with CCR, may not result in a linear change in light
output

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... The PPFD of LEDs can be controlled by PWM or AM, also referred to as continuous current reduction (CCR) [77,78]. PWM entails the use of alternating states in which the current is completely turned either on or off. ...
... A low duty cycle of 10% means that the LED is on for 10% of the on-and-off cycle.
Alternatively, AM is achieved by reducing the current intensity, which in turn leads to decreased light output [77,78].

The luminous efficacy of the two dimming methods varies, though AM can reach 200% of the nominal efficacy of an LED provided by the supplier when dimmed to 10% of its nominal current. ...

... The luminous efficacy of the two dimming methods varies, though AM can reach 200% of the nominal efficacy of an LED provided by the supplier when dimmed to 10% of its nominal current.
Conversely, at the same dimming level, PWM provides only 70% of the nominal efficacy [77].
AM dimming can be used to prevent photoinhibition during early growth stages because photons are emitted continuously over time at low PPFD. ...

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PD...Gracias...por tu Like ....añado mas info...

Lighting Control Technologies: Dimming LED Lights with PWM, CCR, DALI, DMX, 0-10V


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lazaah said:

Hey guys, looking at how I should go about running my new lights from @Grow Lights Australia.

I've got two of the new double units in a 4x4x6 box. So a total of 960w. This is in excess of my current requirements.

I'm working with the PAR maps of their previous lights as they haven't released maps for their new ones (nudge nudge).

I guess my question is, does PPFD decrease linearly with drive current or PWM duty cycle? I'd like to dim them, however I'd like to have a ballpark figure of PPFD at the canopy so I know what I'm working with. I'd prefer to dim them using PWM over current, as my controller can then log the approximate light intensity

Click to expand...

Hi mate we're waiting on LED Teknik to supply us the IES files. Trust me, we've been nagging for some time

To answer your question it is not a linear drop-off as LEDs are less efficient at higher currents – although the new boards do not drop off as fast as the old boards as they have improved efficiency at higher currents (around 2.7 umol/j at 5A or 235W).

It's possible to get a good approximation by using the old IES files as the light footprints and iso-lines are very similar. The only thing that will be different is the actual PPFD readings which will be about 20% higher at the same wattage and height.

So if you tell me your target PPFD for full power and dimmed power I can create a PAR map based on the old boards that will be pretty close. I'll also need your target hang height to see if it is OK or needs to be adjusted up or down.

In future, if you need anything like this just email us at [email protected] and we can get you an answer in a more timely manner.