8 on 8 off light cycle

[SantaMonica]

Iron may also help a burning screen.

[MorganAtlanta]

I set it for 8 on / 8 off after the last cleaning, so we'll see how it goes. My thought is that if it works, I'll split the screen and do the two halves on alternating 8 on / 8 off cycles so that I always have filtration happening.

[kerry]

Kerry: Correct me if I am wrong but I highly doubt that respiration occurs between the flashes when using
PWM.

WannaRace: Based on absulutely no scintific evidence, it seems like you ought to keep the length of each cycle consistent so that the circadian rythm of the algae can be more easily entrained. Wouldn't it be strange if the sun rose 2 hours early every other day?

Photosynthesis can be completed in as little time of about 1ms. PWM modulation testing has been done for more then a few decades. Before electronic circuits they used wheels with slits cut in them and turned by a variable motor. I have read a lot on this subject and there is a ton of room for improving our scrubbers by this method.
Here is quick read:
And here is the whole write up:Read more: http://www.faqs.org/patents/app/20110179706#b
(Conclusion

[0093] The use of Pulse-Amplitude Modulation Fluorometry to assess the bioenergetic state of the photosynthetic organisms under continuous and modulated illumination demonstrated measurable changes in the fluorescence response of chlorophyll a. [0094] 1. It was found that pulsed LED's can dramatically affect the Chlorophyll a fluorescence kinetics leading to decreased NPQ, and enhanced photosynthetic yield and photochemistry. [0095] 2. Many of the modulated treatments exhibited similar decreases in excess energy dissipation and increases in photosynthetic capacity probably due to the similarities in the provided dark periods. These dark periods allow the dark reactions of photosynthesis time to process and the reaction centers time to re-oxidize to a fully open state offering maximal capacity for exciton capture and electron transfer efficiency. [0096] 3. The PAM's ability to detect small changes in the way energy is transferred through photosystem II demonstrates how this sensitive technique could be used to optimize artificial illumination for cultivation of plants or algae. [0097] 4. This study found that the non-photochemical quenching (NPQ) is optimally minimized by a dark period duration no less than 300 μs, then gradually increase above 1 ms. [0098] 5. An increase in the effective photosynthetic efficiency (Yield) of approximately >400% and an additional increase in photochemical quenching (qP) ranging from ˜200-500% was exhibited by all samples treated with pulsed light than the control using continuous illumination. [0099] 6. These results not only confirm the highly beneficial nature of the flashing light effect in terms of chlorophyll reaction kinetics, but also open exciting new applications for optimizing photosynthesis in real-time with a PAM fluorometric monitoring system.

)

[kaskiles]

Wow, so if you used PWM dimming LED driver, and set it to 50% for 24 hours, you would get about the same photosynthesis as a 12 hour light / 12 hour dark combination? But the main difference is that the nutrient uptake and CO2 utilization would be spread out evenly throughout the 24 hour period?

[kerry]

I really think there is a ton of potential here but I have not moved forward with it yet.

[walleyefisher]

I recently started an L2 with a brand new screen and have been running the light 24/7. In less than 1 week I've had an interesting result. I have 3 or 4 places on the screen that algae has grabbed ahold and is growing like mad but other areas on the screen still dont have any growth. I thought this interesting since when I started my last screen I went with the 8/16 schedule and it took a month before I had solid black growth across the entire screen. Only after I bumped my hours to 18/6 did the algae turn green and flourished. I'd wager to say that within 2 weeks I will have a fully green and working screen from new. Then I will reduce hours to 18/6 or 20/4

[MorganAtlanta]

Good harvest with the 8/8 cycle. I'm going to keep going with it.

[tomservo]

I have been using 6/6/6/6 for months already, and my friends for somewhat less time. It works, there is definitely more growth and less burning.

This PWM business sounds interesting but there's probably more to it than just pulsing the lights on and off - I'm sure there are specific frequencies to pulse at to match the respiration cycle or whatever of the specific plant/algea.

[kerry]

For giggles I have my 10G set-up pulsing right now. I just put a driver on the LED's that to big so it does the safety thing and flashes. I have been doing this for about two weeks and there seems to be more growth but I still have a couple more months to go to be sure but, so far it shows promise. I am running it like this 24/7 with no off periods.