PAR Readings - what are good readings ?

[tubamanandy]

Despite an extensive search, cant seem to find any good information on what eg. Good/Average/Poor PAR readings should be at eg. 18", 24", 30" depths.

Can you give me some pointers ?

 

[wazuck]

I wouldn't read too much into unless using leds. Just follow this and make sure your co2 and flow are dialed in well and all should be good. Hope that helps.

 

[tubamanandy]

Useful, but, it was really the PAR figures I was trying to find

 

[ceg4048]

Hello,
The concept of good/average/poor PAR values only has meaning in relation to the level of CO2 being injected. If CO2 is being injected then the injection efficiency and the gas distribution will be factors for good/average/poor PAR.

To simplify, and to have a more meaningful use of the PAR values, consider that in general, PAR measured at the substrate level will determine whether the lighting is low, medium or high. That is what wazuck was showing in his chart and I think that is what you should focus on. Once you know whether your lighting is low/medium/high then,as wazuck mentions, you can determine what steps are necessary to have good/average/poor.

If PAR at the substrate level is approximately 50 micromoles or less, this is generally considered low light.
If PAR at the substrate level is between 50-150 micromoles, this is generally considered medium light.
If PAR at the substrate level exceeds 150 micromoles, this is generally considered high light.

Notice that I've only listed measurement at the substrate. This measurement is used as a proxy for the PAR values at other heights above the substrate because the light will roughly follow the inverse square rule. So depending on the height of the tank, the PAR values will increase to some maximum value at the water's surface.

Because most plants grow vertically they are always faced with a variety of PAR values. The leaves at the top of the plant will encounter a higher PAR than the leaves at the bottom of the plant. So it's not really possible to define any one PAR value as being optimal because each leaf must allocate resources to assimilate the light, nutrients and CO2 at their vertical location, which will differ greatly from the conditions at other vertical locations along the stem.

So, if you have a PAR meter and you do not wish to inject CO2, then you know that you should, in general, keep the PAR value at the substrate to less than 50 micromoles, and that will be good or average. If you insisted on using the 150 micromole level then this would be considered poor, because it would be too much and the plants would most likely suffer CO2 deficiency. However, if you then installed a CO2 injection system, and if you installed a good flow/distribution system, then the 150 micromole reading would be considered good/average. If you kept the CO2 system in place and then reduced the substrate PAR value back to 50, then this would still be considered good/average.

Cheers,

 

[tubamanandy]

Brilliant Ceg and many thanks - just what I was looking for.

 

[tubamanandy]

Can you believe it, just found this - however, readings appear to be greatly different from those kindly given above.

Low light - 15-30 micromols of PAR - CO2 is not needed, but is helpful to the plants
Medium light - 35-50 micromols of PAR - CO2 may be needed to avoid too many nuisance algae problems
High light - more than 50 micromols of PAR - pressurized CO2 is essential to avoid major algae problems

 

[George Farmer]

Can you believe it, just found this - however, readings appear to be greatly different from those kindly given above.

Low light - 15-30 micromols of PAR - CO2 is not needed, but is helpful to the plants
Medium light - 35-50 micromols of PAR - CO2 may be needed to avoid too many nuisance algae problems
High light - more than 50 micromols of PAR - pressurized CO2 is essential to avoid major algae problems

Absolutely no disrespect to Clive but I'd be more inclined to go with these values.

The PAR in my current tank is about 30-40 at the substrate and I'm seeing very fast growth. I dread to think how I'd manage with anything over 100. 150 is almost SPS coral territory.

 

[Ady34]

Are the par readings for low, medium and high based on dry tank results or submersed readings? How much effect does this have on the values given?
What is the general consensus when taking readings, dry or wet?.....I don't know anything about par meters, can you even get waterproof ones, or is there some sort of calculation for the effect water has on par from a dry reading?
Cheers
Ady

 

[George Farmer]

These readings are all based on the PAR being measured submerged at the substrate level, so it's a measurement of the minimum light the plant is likely to receive. 🙂

PAR drops off considerably more under water than air, given the same distance from the light source to the target.

 

[Ady34]

Cheers George 🙂

Would you say the table above is fairly representative as a rough guide to the high medium and low readings also then?
Cheerio

 

[George Farmer]

It seems feasible - certainly better than the watts per gal. guidelines that were originally drawn up with T12 fluorescents in mind. I think I did a similar table for a lighting article in PFK a while back.

I think the biggest lesson I've learnt in recent years is that too much emphasis is often placed on lighting intensity, spectrums, colour temperatures etc. for planted tanks. It's not surprising though, given that the fundamental element required for plant growth is light... but most of us are now aware that there's very few plant species that actually require high lighting (>50 PAR), especially now principles of good CO2 and other nutrient management are well-known (on UKAPS, at least...)

Just as folk are learning to accept that NP doesn't cause algae in planted tanks, I think the next step forward should be that hobbyists use less light, and concentrate more on decent CO2 management (if used) and overall maintenance practices. Then the amount of topics asking about algae issues will drop considerably. 🙂

I digress. 🙂

 

[ceg4048]

Hi George,
I totally agree with you and I like those numbers even better.🙂
I'm still a Megawatt Loving Kilingon (MLK) at heart....

Cheers,

 

[Ady34]

It seems feasible - certainly better than the watts per gal. guidelines that were originally drawn up with T12 fluorescents in mind. I think I did a similar table for a lighting article in PFK a while back.

I think the biggest lesson I've learnt in recent years is that too much emphasis is often placed on lighting intensity, spectrums, colour temperatures etc. for planted tanks. It's not surprising though, given that the fundamental element required for plant growth is light... but most of us are now aware that there's very few plant species that actually require high lighting (>50 PAR), especially now principles of good CO2 and other nutrient management are well-known (on UKAPS, at least...)

Just as folk are learning to accept that NP doesn't cause algae in planted tanks, I think the next step forward should be that hobbyists use less light, and concentrate more on decent CO2 management (if used) and overall maintenance practices. Then the amount of topics asking about algae issues will drop considerably. 🙂

I digress. 🙂

Yeah agreed, i only asked as i was quite surprised that 2x t5 12" above the water surface would still be classed as medium light.....with nothing really to go on (par readings), and the old wpg rule being rather out of date, i was guessing that my light unit approx the same height above the water surface would have been considered low light....but perhaps this means i can raise it further to give more c02 leniency.....(still need to work on injection method and distribution before hanging with the big boys and being a.....

Megawatt Loving Kilingon (MLK)

.....😉 )

This seems a decent thread to also show what may be considered the minimum PAR readings for plants - LCP (Light Compensation Point). No doubt it will differ from species to species but what should be a minimum we aim for before a growth stalemate occurs? Is it simply less than 15 micromols? Im guessing we can roughly use the above table and the shaded Grey areas to give us an idea of the LCP for different bulb ratings and depth tanks? (assuming these are all appropriate length bulbs for the tank)

Cheerio,
Ady.

 

[ceg4048]

Ady,
LCP actually varies according to CO2 availability. It's even possible to have some plants grow with as little as below 10umoles. Also, not all leaves will be at LCP at the same time just because of the light distribution, so it would have to be referenced to the leaf with the highest incident PAR. Having all leaves being below LCP is so rare, I would doubt it's usefulness.

Careful. Once you morph into an MLK, only death can release you from your bond...

Cheers,

 

[xim]

These readings are all based on the PAR being measured submerged at the substrate level, so it's a measurement of the minimum light the plant is likely to receive. 🙂

PAR drops off considerably more under water than air, given the same distance from the light source to the target.

Yes that's true. But for tank sizes we keep, the PAR can be higher when filling with water because of reflection. 🙂
Try looking at charts #2 and #3 : Lighting an Aquarium with PAR instead of Watts

 

[tubamanandy]

Thanks guys, got exactly the answers I was looking for, especially as a new member