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Hoppy 04-04-2010 07:55 PM

PAR vs Distance, T5, T12, PC - New Chart
I suggest using this much more up to date thread, which will be updated as necessary, 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:

killacross 04-04-2010 09:08 PM

you left our spiral CF bulbs but either way...cant wait to see how this thread will evolve..especially if i4x4 gets involved and you two heavy weights can duke it out...(dont be Roy Jones Hoppy! lol)

thank you for never letting this subject die!

Hoppy 04-04-2010 09:46 PM

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!

killacross 04-04-2010 10:00 PM

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


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)

plantbrain 04-04-2010 11:43 PM

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.

Tom Barr

wkndracer 04-05-2010 02:20 AM

Thanks again Hoppy.

sanj 04-06-2010 09:42 PM

Hello Hoppy,

thanks for doing this test, informative and interesting.

shoggoth43 04-07-2010 12:35 PM

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.


Hoppy 04-07-2010 03:56 PM

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.

GTR 04-07-2010 04:18 PM

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


Hoppy 04-07-2010 08:08 PM


Originally Posted by GTR (Post 1040656)
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


I think you might gain another 30-40% if you used a somewhat parabolic, highly polished aluminum (MIRO 4) reflector, that was big enough for that size bulb. That would barely be a significant increase.

speedie408 04-07-2010 08:29 PM

Great brain food.

insta 04-07-2010 09:44 PM

Hoppy, if I reflectorize my little DIY LED fixture and mail it to you, would you mind running it through this same test?

SemperFish 04-07-2010 10:40 PM

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.

shoggoth43 04-09-2010 03:15 PM

Well, I've got a Tek5. I was just curious if there might be any reason to retrofit the ballasts and such at some point since the T5NO lights are somewhat easier to find without going to a supply store. I think the reflectors in those are pretty decent.


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