Dimming or reduced time?

[Chris_Homan]

New tank, 90l Superfish Aquascaper with standard LED strip. No CO2.

I would like to keep my lights on for as long as I can but know this will cause algae to grow. Now what is better, reducing the time lights are on or reducing brightness with a dimmer?

 

[Nick potts]

Both will achieve the same result.

Drop the brightness right down and slowly raise it over several weeks/months.

 

[ceg4048]

Both will achieve the same result.

Hi Nick,
This is not technically correct. Damage to plant tissues is primarily done by excessive intensity when the level of CO2 is inadequate. This results in a toxic buildup of electrons which then forms radicals such as Hydrogen Peroxide within the plant tissues which damages the tissues - essentially eating the plant from the inside.
If the intensity is too high then of course, the damage will be exacerbated by long duration. If the light intensity is low however then the duration has much less effect, there is a greater likelihood that the CO2 shortage will not be as acute and the plant can spend a lot of time under low intensity without problems since radical production will be limited.

Always therefore reduce intensity first.

Cheers,

 

[MichaelJ]

@Chris_Homan, by far, intensity (brightness) is the most important factor. I run my light intensity very low, and have tons of floating plants (frogbit) in both my two densely planted non-CO2 tanks, but I keep the photoperiod for a solid 12 hours including sunrise/sunset ramping (kind of like it is around the equator where most of our livestock is from originally). And now I at least have a sense of why it works thanks to @ceg4048's explanation above. An added bonus of running the lights for long hours is that I get more opportunities to enjoy my tanks!

Cheers,
Michael

 

[oreo57]

Granted the below vid is for corals so just food for thought. As to my own opinion, I' m not convinced either way as long as one is not pushing much past the light compensation point like 50 par for 12 hours vs 75 for 8 hours. 200 par for 3 hours might be an issue though exact effects are ???
Carotenoids and peroxides :

Carotenoid oxidation products are stress signals that mediate gene responses to singlet oxygen in plants

1O2 (singlet oxygen) is a reactive O2 species produced from triplet excited chlorophylls in the chloroplasts, especially when plants are exposed to excess light energy. Similarly to other active O2 species, 1O2 has a dual effect: It is toxic, causing oxidation of biomolecules, and it can act as...

www.pnas.org

[18] Functions of carotenoids in photosynthesis

Carotenoids are essential for the survival of photosynthetic organisms. Carotenoids have been shown to have two major functions in photosynthesis. The…

www.sciencedirect.com

Obviously nutrients need to be available in all situations
Go to about 5:00.

we

 

[ceg4048]

Granted the below vid is for corals so just food for thought. As to my own opinion, I' m not convinced either way as long as one is not pushing much past the light compensation point like 50 par for 12 hours vs 75 for 8 hours. 200 par for 3 hours might be an issue though exact effects are ???

Very difficult to draw parallels with corals because other than the basic processes the mechanisms are different. Whereas direct chloroplast interaction occurs in freshwater plants the corals are interacting via symbiosis with zooplankton intermediaries.
Plants have direct interactions via their chloroplasts and the superoxides have direct effects on their tissues.
It's not possible to predict what the effects of the PAR increases are without knowledge of the CO2 in those circumstances. 50 micromoles for 12 hours may be deadly while 200 micromoles for 3 hours may be fine depending on CO2/flow/distribution.
In the OPs case, the CO2 is only at dissolved atmospheric levels and so lowering the light intensity to moderate levels just above LCP will be fine all day long. If he increases the intensity however, then there definitely will be damage, the amount proportional to the intensity increase. In fact, we see examples of this every day. The phenomenon discussed in the video is not completely applicable in our case.

Cheers,

 

[oreo57]

Well yes it was mostly posted to show that differences can occur .
The coral "algae" symbionts "see" the same high light products and damage. It is different but not that much.
In a sense since both are in a relatively CO2(g) limited environment and never water limited coral "algae" may be more reflective than using terrestrials.
Of course our little plants don' t have the luxury of expelling themselves (bleaching) if high light "toxins" threaten to damage themselves.

Why Too Much Light Can Be Harmful to Zooxanthellae

I get private messages about many subjects. This was my response to one such PM: https://reefs.com/magazine/too-much-light/

www.reef2reef.com

Pieces of a complex puzzle

Photosynthesis and photoinhibition in aquatic plants with different carbon uptake physiology

Download Citation | Photosynthesis and photoinhibition in aquatic plants with different carbon uptake physiology | There is ample evidence in existing scientific literature that photorespiration actstowards reducing photoinhibition in plants. The internal... | Find, read and cite all the...

www.researchgate.net

Photoinhibition - Aquatic Ecosystems - Climate Policy Watcher

The inhibition of photosynthesis at high light intensities must be taken into account in ecological studies, since the intensities typically experienced in the

www.climate-policy-watcher.org

Xanthophyll cycle--a mechanism protecting plants against oxidative stress - PubMed

Six different xanthophyll cycles have been described in photosynthetic organisms. All of them protect the photosynthetic apparatus from photodamage caused by light-induced oxidative stress. Overexcitation conditions lead, in the chloroplast, to the over-reduction of the NADP pool and production...

pubmed.ncbi.nlm.nih.gov