Your welcome to stop by anytime. Or punch up a thread. It’s actually quite easy once it’s laid out.
It’s myth and myth understanding that makes it hard.
Light diffusers for SPS......your experiences?
- Thread starter spspirate
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It’s myth and myth understanding that makes it hard.
chefjpaul
2500 Club Member
I will start a thread regarding,
The Seneye reads both lux and par.
I'm not sure on accuracy, but it is consistent.
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Huh? PAR is just a totally flat curve in the 400-700 nm range, LUX is weighted heavily toward the middle of that. I don’t get how lux would be more helpful in our tanks, unless you just want to quantify how bright something looks to a person? Can you give an example of a very bright light with very low PAR?
PAR:
Lux:
I’m really too tired to debate this again and show the pictures of the inside of a par meter.Huh? PAR is just a totally flat curve in the 400-700 nm range, LUX is weighted heavily toward the middle of that. I don’t get how lux would be more helpful in our tanks, unless you just want to quantify how bright something looks to a person? Can you give an example of a very bright light with very low PAR?
PAR:
Lux:
It not more helpful but it is helpful.
if you know it’s good spectrum , you just make it brighter.
A lux meter will do that.
An example of a bright low par light
Cool white florescent tubes.
Where’d you get that lux graph. Its pretty weird. And I belive ,inaccurate.
ttnguyen98
Active Member
I guess that this lux meter is used to measure light intensity above water level.
hyprc
Well-Known Member
It actually does but not to an extreme extent. If you look at the install videos, the bottom plate is replaced with a reflector which can catch light reflected from the diffusor plate and bounce it back, effectively emitting light from nearly the entire bottom of the fixture (at least thats what it looks like to me). This combined with the increased bounce from the glass as mentioned before (BRS's tests found stronger PAR around edges with the diffusor), might help - that's what I'm hoping for from mine at least. As for lost intensity, I plan on increasing my intensity 3 to 5 percent after I add the diffusor.
Google Images. There's a more detailed, explanation with very similar graphs on Wikipedia. I'll quote:
This is all well accepted stuff. Lux is weighted for human perception. Par is a flat weight across 400-700 nm. Lux is basically useless for reef tanks.
Here's a link for the luminosity function: nice, big peak at 550nm or so. https://en.wikipedia.org/wiki/Luminosity_function
That’s cool. I’ve kinda been talking to Dana Riddle recently since he came here and following his work for some time, many years in fact, plus speaking to manufactures of Lights and been working in lighting for close to 30 years.
Wikipedia and google images may not be this most fully comprehensive study in Light is all I’m saying.
If it were useless , apogee and Dana would not have par and lux conversions. The two are linked.
But one does need not understand why.
Similar arguments are constsnly being made about how a Par meter is actually useless in the measurement of Light as well, Kessil for one, and many users and hobbiests as well. Almost daily in fact.
If one truly understands the tools then one can truly understand the results from them. You have to know and understand the big picture of Light and measurement and what is being measured and how.
And that graph is wrong, or a “lux” meter would only meter green. And the labs I get my meters at would not care what color temps they are calibrated at. But they do, or they’d only use green. We would also not be able to take picture or make movies in blue light. Or red. We could not expose film correctly.
So it’s not a fair nor correct representation of a photocells actual Response cuve.
You can get them that do underwater work, Milwaukee makes one.
Or just put it in a zip lock.
But I generally just estimate the par I want at the top of the tank. And target that.
Say for a high light tank that’s 24in , I would shoot for 500 par. A 30 in tank , 700 par. A 12 in deep tank 350par.
For a med light and low light a 24 in deep id target 300 par at the top.
Using lux , you need to convert, most all led so far at a 1:1 ratio come out with a conversion number of 60.
Must t5 combos (14-20k) come in around 50.
So for led 100 par is about 6000 lux.
With more blue it’s actually less. So it’s a good buffer IMO.
This btw is how I guage picking a Light for a tank.
I want 300-500 par at the top. So choose X light. So for example , a kessil 160 or a kessil 360. Will give me what I want , but the ap700 May give me too much. So I’d save some cash.
Is it 25% they documented or did you get this result?
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spspirate
Tidepool Explorer
I guess it would vary by height of the fixture off the water too. Is it as simple as just increasing the intensity?
hyprc
Well-Known Member
Why would height matter if it's a percentage reduction?
I don't see this as a huge negative with a light most are scared to turn up past 65% or so (yes I know some people like to run them maxed out 2' above the water in some cases but that's not the majority). What I'm going to be thinking of when I install the diffusor and turn up intensity is, if I remember correctly from the BRS video, the edges of the tank saw increased PAR lower down in the tank even with the overall reduction. Some items on the sand might need to get moved around a bit due to too much additional light to keep the rest of the tank where it's currently at in PAR. Someone please correct me if I'm wrong (I'm still admittedly a n00b).
Servillius
Active Member
Lux is not ideal by a long shot as you say. It does have one handy use in a tank though. If your light source is homogeneous (LED is not), you can make relative comparisons. If my lux is 1500 in one spot and 1000 in another, I’m getting 2/3 the light in the second spot. Once you’ve established a baseline with a PAR meter, with older lighting, this is pretty handy.
As for the diffusers themselves, they accomplish two things. First, they scatter some of the light. This improves color mixing. It also causes some light to fire off at different angles. The absence of random scatter with LED lights can cause shaded spots and disco ball effects even with the best lights. The diffuser will help even this out. There will also be some absorption and remission going on which will reduce output and shift spectrum some. I have no idea how significant this is with the Ecotdch diffuser. My guess is the relative amount of light under a large overhang will be greater with the diffuser making it easier to grow low light species in darker areas. You would also see less dieoff lower down on larger corals.
I would also guess that the scatter issue is producing a misleadingly large drop in par. Corals are three dimensional. The meter is not. That scattered light will appear as lost light to a 2d sensor (they’re not all totally 2d, but they all miss some of the light coming from off angle sources) because the angle of attack is such that the sensor doesn’t get hit with it or because some energy is deflected, etc. For instance light coming from below is totally lost. If there is more light coming from below however, Corals can use it.
Imagine a system with 1000 par from above and 10 par reflected. In a very, very simplified sense, half the coral gets 1000 and half gets 10. Since coral can only really use 200 (again, arbitrary ballpark number), the whole coral is using 210/2 par or 105 par. If a diffuser reduces 1000 to 750 and scatters the rest, The reflected light could go up to 100 for instance. Now the whole coral is using 300/2 or 150 par. It’s also being less photoinhibited at the peaks. Net result, more better light.
Sorry, crammed in a lot of thoughts in a reply to one person. I suppose most of it is directed to the topic generally and not one poster
I can see this a little bit. However, with the loss in output, how does anybody know that it is going to be any better? Should the smart/responsible advice be to say that it is just different, for now?
FlyinBryan
Well-Known Member
It may be too early to tell what the long term impact will be. So far everything looks good but will keep track of growth and color. I’m running a small experiment myself. Before & after pics on a time line.
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spspirate
Tidepool Explorer
You got a point
hyprc
Well-Known Member
That's fair. I'd encourage you to watch BRS's video on the diffusor if you haven't already though. It's fair to assume that the difference may not be significant at this point, hopefully time will tell definitively (but do we every truly have that luxury in this hobby? heh).
spspirate: thank you; love your first quote in sig btw. As for the second, reefing is my best therapy so might be spending MORE in that sense lol
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