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PAR vs Distance, T5, T12, PC - New Chart

362K views 775 replies 230 participants last post by  Hoppy 
#1 · (Edited)
I suggest using this much more up to date thread, which will be updated as necessary, http://www.plantedtank.net/forums/showthread.php?t=184368 instead of proceeding here.

I have been wondering how much PAR a typical T12 light produces. Like most everyone else I have just assumed that watts per gallon was a way to guess the light from T12 bulbs, but there is no more reason to expect that to mean anything than there is to expect it to mean anything for other bulb types. So, I decided to do some testing.

I borrowed a new two bulb 48 inch T12 light fixture from one of our local aquatic plant club members, bought a new T12 bulb - a Phillips "Natural Sunshine", 40 watt 5000K, 92 CRI bulb at HD, borrowed our club PAR meter and took some readings. Since I have previously found that I get virtually the same readings with water in the tank and with air in the tank, I omitted the water this time. Then I plotted my smoothed data on a common plot with T5 and PC data:



To compare this with "watts per gallon", I know that a couple of 2 bulb T12 fixtures will grow plants in a 55 gallon tank. That tank is 20 inches deep, so if the substrate thickness is about the same as the height of the bulbs above the top of the tank, each bulb should give about 9 micromols of PAR, or 36 micromols for 4 bulbs. That is right in the middle of the low light range. So my data is consistent with real life results.

The light fixture I borrowed has an acrylic splash shield and a removable back, which is a white reflector. I tested the light with and without the splash shield to find that the shield reduces the intensity about 7%. Testing with and without the white "reflector" shows that the reflector increases the intensity by about 36%. The data used for the chart is with both the shield and the reflector.

Some popular tanks are only 12 inches high. For those tanks T12 bulbs should give about 25 micromols per bulb, so a 2 bulb fixture will give low medium light intensity, probably a good choice for many people with one of those tanks.

I believe T8 bulbs produce about the same amount of light as T12 bulbs, but at a lower wattage, because they are more efficient. The fixture I borrowed uses starters and magnetic ballasts, so I didn't try it with a T8 bulb.

EDIT: Updated chart above and added the following chart:
Another way to use this is to convert it into a simple table, that lets you select a lighting option based on tank height, how high you want the light to be above the top of that tank, and how much light you want. This assumes that multiple bulbs are mounted close together, reflectors are typical for that particular type of light. And, I left out the AH Supply light kits.


EDIT (again) New chart added.

The T5HO line on the first chart has been difficult to apply, because so many cheap T5HO lights with less than good reflectors are now available. To make it easier to estimate how much light you can get from different quality T5HO lights, try this chart:

And, to judge the quality of the reflectors:
 
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#3 ·
Spiral CF bulbs are a different breed of light. The ones on that chart are all linear tubes which tend to produce the same PAR for any length of bulb, with the length to be used depending only on the length of the tank they are to be used over. But, spiral bulbs have varying lengths twisted together to get all of the light emitted over one small area. There is a thread in the stickies that I think covers those bulbs as well as they can be, for now.

I have enjoyed working with lights since I worked for NASA many years ago, when I was working on a "bulb" that was a water cooled tungsten arc bulb, using argon as the gas flowing through it. Now, that was BRIGHT!
 
#4 ·
what about the new sulfur-plasma bulbs? Ill have to find a link because I cant remember where I saw it...

they demoed one to show the range of intensities (like 5%-95%) once at the university and we all saw spots for a while

***edit***
http://www.sulphurplasma.com/

really, I find the lighting interesting because its usually the easiest "upgrade" we can make to a tank

but really Im trying to find a way to upgrade the light in my projector from teh standard halogen/xenon/whatever bulbs to a high intensity LED (tho LEDs lack the throw distance :-/- but one day Ill buy 1 $200 bulb thatll last 20years)
 
#5 ·
So 2.9W/gal for 4x 40 W T12's on a 55 gal tank is still lower light than 40micromols........

So around 3W/gal is considered high light by many that use the conversion, then they run out and apply it to a T5 or a PC light set up and assume they are the same.

I'm not sure why testing is so horrible for lighting when so many on the forums over the years harass people about the need to test things like NO3 or PO4 critically, or Fe and Mg etc......balancing K+ and all sorts of hoodoo.

Then do not measure light.

CO2 has it's many issues, but light is fairly straight forward and not hard if you use a meter. Hoppy's graphs illustrate the point pretty clearly.

Does not matter what differences tank to tank we might have, with a PAR meter, you have a good idea for comparisons. Quick, easy and lightly(pun intended) do not have to do it again from then on. Cost is the main issue for the PAR meter, some have suggested renting, but many are too cheap even for that, but are willing to spend $$$ for test kits.
You can also buy it, use it, rent amongst local folks, then sell it.

Why would you need it much more unless you are like Hoppy or myself interested in doing comparisons in real or hypothetical cases?

Might as well sell it back for 200$ or so.
If you buy it for 200-240 in a group buy, it cost you next to nothing.

Folks will buy them for the 200$ range pretty easily.

Regards,
Tom Barr
 
#8 ·
T5?

Where do you suppose a T5NO ( normal output like at HD ) would fit in this graph? In theory they put out more light per watt but at less watts than the T5HO I'm not really sure if they'd be nearer the PC graph or below it since I've really got nothing to compare it to.

-
S
 
#9 ·
I haven't tested T5NO lights, nor have I seen any data from anyone else for them. I do know that T5NO lights are more efficient than T5HO - more light per watt - and T5NO lights are a bit more than half the wattage of T5HO lights. So, a T5NO light should produce more than half the light that a T5HO light does, but only if it has the same quality of single bulb reflector. Unfortunately, I don't think any T5NO light does have the same quality reflector. I think the best guess I can make is that a 2 bulb T5NO light will produce about the same PAR as a typical one bulb T5HO light. I suspect it produces less PAR than that.

And, remember, AH Supply PC light fixtures have uniquely great reflectors. Coralife fixtures, for example, don't have nearly as good reflectors. And, many cheap PC light fixtures effectively have no reflector at all, because they allow no room for one. They might produce only half the PAR as an AH Supply light.
 
#10 ·
So if you had a decent reflector for T-12 what would you guess the increase would be.

Not sure there's a valid reason to use them anymore but having used them for 25 years it's like losing an old friend. lol

SteveU
 
#14 ·
Great information for a planted noob like me. Would you answer a question for me? I plan to step up from a low tech 29 gal to a low tech 55 gal. I'm considering going with either 3x32 watt T-8s or 3x28 watt T-5 NO's. I do plan on doing an occasion excel dose, using eco complete, and low light/hard to kill plants. Would these choices be good lighting for what I want? Suggestions....Thanks in advance.
 
#17 ·
3 T8 bulbs on a 55 gallon tank, 20 inches high, or 1 T5NO bulb, should give you low light. Or 2 T5NO bulbs should give medium light. Of course if you choose to hang your light above the top of the tank, which I think is the best way to light a tank, you could use even a single T5HO light - hanging 4-5 inches above the top of the tank, to get low medium light. That gives you the best uniformity of light in the tank.
 
#18 ·
Great info Hoppy.
I am not sure if I should start another thread or use this one but I am starting a 40 breeder tank. 17" Tall with a 3" or so substrate (flourite black). Lights are Catalina 3x39 T5ho ( I will most likely only use the two outer bulbs)
I will have pressurized Co2 and will be dosing EI. I plan on having a carpet (undecided between UG or HC) Stems in the back (Rotalas? Etc.)
I have flip legs for the lights but it seems hanging would be better according to the graph. if I am reading correctly (for the upper end of medium to low end of high light) I should hang the fixture 25 or so inches from the substrate. Is this right? Given my goals would you change anything regarding the set up? Change the number of bulbs used and/or the height? I really dont want algaefest 2010.
I hope you can shed some "light" on the subject, so to speak.
Thanks,
Nate
 
#19 ·
25 inches above the substrate (11 inches above the top of the tank) looks about right to get 80 micromols of PAR at the substrate using 2 bulbs in your Catalina 3x39 T5HO fixture.
 
#21 ·
I have been wondering how much PAR a typical T12 light produces. Like most everyone else I have just assumed that watts per gallon was a way to guess the light from T12 bulbs, but there is no more reason to expect that to mean anything than there is to expect it to mean anything for other bulb types. So, I decided to do some testing.

I borrowed a new two bulb 48 inch T12 light fixture from one of our local aquatic plant club members, bought a new T12 bulb - a Phillips "Natural Sunshine", 40 watt 5000K, 92 CRI bulb at HD, borrowed our club PAR meter and took some readings.
So you put one bulb in a two-bulb fixture?

I have two-bulb T12 shop lights, and when I install only one bulb, it lights up very dimly until I pop in the other bulb. Did you ever install a second bulb to see if there was a change in brightness?

I wonder if this could have given you incorrect data...
 
#22 ·
I didn't try two bulbs because I didn't want to pay for two. But, the bulb lit up as brightly as I usually see, anything but dimly. I don't recall any previous magnetic ballasted T12 fixture I have used doing what you saw, but I don't rule it out. The fixture had two power cords, two switches, so I assumed it was intended to run one bulb alone if desired.
 
#25 ·
I did some experimenting with mylar, aluminum foil, and ordinary white paint as reflectors. To my surprise, the mylar was the least effective, the aluminum foil the most effective, but just barely better than white paint. I didn't use any special white paint, just what I had in a spray can at the time. I believe if you take care to get an ultra white paint you will get better results with that than with aluminum foil, and certainly better than with mylar. The differences I found were around 15-20% from best to worst, so the light doesn't look much different, but a PAR meter shows the differences.
 
#26 · (Edited)
Today, I went back over the data I received from others about various types of bulbs and fixtures, and realized that I could characterize non-AHS PC lights as well as the AHS lights, and that I had one data point for a 150 watt HQI fixture. So, I added that to my chart of PAR vs distance, double checking how I derived that chart. It changed a little, on double checking, but not significantly. Of course the HQI line is just there for comparison, it isn't nearly good enough to use for selecting that type of fixture. The other lines should be good enough to get you into the low, medium or high light categories pretty reliably.


EDIT:
Another way to use this is to convert it into a simple table, that lets you select a lighting option based on tank height, how high you want the light to be above the top of that tank, and how much light you want. This assumes that multiple bulbs are mounted close together, reflectors are typical for that particular type of light. And, I left out the AH Supply light kits.
 
#29 ·
I have read a lot about T8/T12 vs T5HO but found little info on overdriven T8 vs anything.
ODNO T8 output increases over normal T8 (from GulfCoastAquarian's ODNO thread):


  • 2xODNO (2 power leads per bulb) - ~50% increase
  • 3xODNO (3 power leads per bulb) - ~75% increase
  • 4xODNO (4 power leads per bulb) - ~100% increase
 
#30 ·
So assuming 1 T8NO@20" gives ~10par, 1 T8ODNO 2X would yield ~20par. If I also assume that 1 T5NO gives about half the par of T5HO, I would get ~30par@20" for T5NO.

The T5NO would yield ~10par more over the T8ODNO, that's not a lot but it gets onto the low light range(barley) for 20" depth.

Does this sound right?
 
#32 ·
What's the conversion factor from LUX to PAR? I understand it would't be exact because of what PAR and LUX are and that different bulbs perform differently throughout the spectrum. Still, it would be useful information to have a ball-park idea of how the two compare from an average bulb.
 
#34 ·
I haven't tried to determine the answer to that. Most bulb manufacturers don't print the LUX @ X inches rating on their bulb packages, so I never felt it was an important thing to know. I do know that the conversion factor would be much different for a GE9325K bulb, a 6500K cool white bulb, a 10,000K bulb, etc. How much different I don't know either. Someone else can have the fun of figuring this out:smile:

T5NO lights are interesting. I read a few years ago that the efficiency for converting watts to light for a T5NO bulb is higher than for a T5HO bulb. And, I know that for any given length bulb, T5NO bulbs are a little more than half the wattage of T5HO bulbs. From that you could assume that a 2 bulb fixture with T5NO bulbs would produce about the same or a little more PAR than a one bulb T5HO fixture. Except, that few T5NO fixtures use reflectors that are nearly as good as typical T5HO fixtures. And, the reflector accounts for a big percentage of the efficiency of T5 bulbs. Until someone gets several PAR meter reading for a few different T5NO fixtures I don't know how we will ever know how to judge those fixtures.
 
#35 ·
tom and hoppy where do you think my 192w (2x96w) power compact bulbs stand in the line of par now that they are over 2-20H tanks with the lights beening 18-20 from the substrate, oh and I also have c02 now just need to get the bottle filled and recert.
 
#38 ·
Those tanks are 24 inches long, right? And, they are end to end, or 48 inches total length? With a pair of 35 inch long lights sitting on the top of the tanks? Assuming that is all correct, the half of each tank directly under the pair of bulbs, which have to be close together, given the 12 inch depth of the tanks, would be about twice what one bulb would give.

The big unknown is whether these are like AH Supply light kits, or like Coralife light fixtures. If like AH Supply, the PAR would be around 100 micromols of PAR, but if like Coralife, it would be more like 40 micromols of PAR. At the end of each tank not directly under the bulbs, the intensity would be quite a bit less.
 
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