Lux readings for T12 & T8 Aquarium Hood
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Old 09-03-2012, 05:16 AM   #1
sowNreap
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Lux readings for T12 & T8 Aquarium Hood


Edit: 1/17/2013 .. I've updated the PAR values based on the corrected conversion factor of 76.

My single bulb All-Glass 48" aquarium hood accepted both the T12 and T8 bulbs. So did readings for both.

Also did my 2 bulb T12 white painted shop light with aluminum foil lining. It would NOT take the T8 bulb. I took readings both foil lined and white painted surface. Not sure if they'll help but I wanted to know for my own purpose so figured I'd post them.

Here's some pics. My aquarium hood with T12 bulb. Didn't take pic with T8 bulb. You can see a at least 1 bulb reflection on the left and partial on the right which probably doesn't do much since it's so straight and not a good angle "/".



Here's my aluminum foil lined shop light. No real bulb reflections visible just a very faint reflection. And I probably should have done better job smoothing the foil.



Right off the bat I'm going to say the aquarium hood hangs tilted toward the front. I couldn't get the hangers where they needed to be to counter-balance the fixture to hang level. So the T12 readings may be a bit higher because it was closer to the wall which seems to enhance the light. Did 2 readings each bulb. The 2nd reading for the T8 bulb I turned fixture around so it was tilted toward front to see how the light bouncing off the wall effected the readings.

Aquarium Hood - Center of fixture
Height -- T12 Lux/Par ---- T12 Lux/Par ----T8 Lux/Par -----T8 Lux/Par
15 -------- 232/38.0 ---------- 234/38.3 --------- 337/55.2 -------- 325/53.3
20 -------- 163/26.7 ---------- 166/27.2 --------- 235/38.5 -------- 229/37.5
25 -------- 122/20.0 -----------123/20.2 --------- 175/28.7--------- 170/27.9
30 ------ 947x1/15.5 -------- 950x1/15.8 -------- 135/22.1--------- 132/21.6


Aquarium Hood - Center of fixture
Height -- T12 Lux/Par ---- T12 Lux/Par ----T8 Lux/Par -----T8 Lux/Par

15 -------- 232/30.5 ---------- 234/30.9 --------- 337/44.3 -------- 325/42.8
20 -------- 163/21.3 ---------- 166/21.8 --------- 235/30.9 -------- 229/30.1
25 -------- 122/16.1 -----------123/16.2 --------- 175/23.0--------- 170/22.4
30 ------ 947x1/12.5 -------- 950x1/12.5 -------- 135/17.8--------- 132/17.4


2 bulb T12 fixture on the 2nd no foil reading I turned the bulb slightly and noticed it got brighter so it's more accurate.
Height Foil Lux/Par --- No Foil Lux/Par -----No Foil Lux/Par
15 -------- 381/62.5 --------- 344/56.4 ------------ 372/61.0
20 -------- 278/45.6 --------- 248/40.7 ------------ 275/45.1
25 -------- 210/34.4 ----------190/31.1 ------------ 202/33.4
30 -------- 164/26.9 ----------145/23.8 ------------ 154/25.2


2 bulb T12 fixture on the 2nd no foil reading I turned the bulb slightly and noticed it got brighter so it's more accurate.
Height Foil Lux/Par --- No Foil Lux/Par -----No Foil Lux/Par
15 -------- 381/50.1 --------- 344/45.3 ------------ 372/49.0
20 -------- 278/36.6 --------- 248/32.6 ------------ 275/36.2
25 -------- 210/27.6 ----------190/25.0 ------------ 202/26.6
30 -------- 164/21.6 ----------145/19.1 ------------ 154/20.3


Hopefully I did all my math correctly converting the PAR. And that this helps somehow. I can definitely see that T8 bulb puts out about 40% more light than the T12 does at least in that fixture. And that the aluminum foil doesn't really do any better than the white painted surface ... if you disregard the 1st no foil reading where the bulb wasn't seated good.

Hoppy, how does this compare with your T8 readings?

Edit: All bulbs were 6500k daylight bulbs. T8's bought a month or so ago when I bought the diamond plate fixture. T12's were bought April or May I think.

Last edited by sowNreap; 01-17-2013 at 04:42 PM.. Reason: add info
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Old 09-04-2012, 01:26 AM   #2
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I plotted the data for the T8 bulb:



It seems high, but that is a good reflector, as shown in the photo, and it would look even better with the T8 bulb in it. (Can you still get a photo of it with the T8 bulb, to put in the PAR vs Distance thread?)
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Old 09-04-2012, 02:00 AM   #3
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Sure .. I'll get that photo with the T8 maybe tonight. It probably does make a bit of difference with that right side reflector since the bulb is smaller.

I was a bit surprised about how it did but I'm pretty sure my readings are accurate. As a matter of fact when I take the pics I'll do another reading just to see how it compares since I'll have the bulb in it anyway.
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Old 09-04-2012, 04:58 AM   #4
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Here's a close up photo of my aquarium hood. This one turned out best because you can see 4 bulb reflections. Not only that but that front reflection is so good it's almost hard to tell it's not another bulb.



I took some more readings while I had the bulb in. I took 2 as the fixture normally hangs .. tilted toward the front should compare to previous readings. I then rigged up something to try to level fixture (eyeballed only, didn't put a level on it LOL) which made the lux readings go up. So the angle can also effect the readings. The measurements were to the bulb itself no matter how it hung.

I didn't purposely try to get the exact readings in the 3rd & 4th columns. It just came out that way. I actually moved the fixture all the way back down to 15” and worked my way back up each time. Even though I'm using 1/2" link chain for some reason it seems to get off by 1/8"-1/4" at different heights so have to still make minor adjustments.

Aquarium Hood - Center of fixture
Height ---Tilted Lux/Par -----Tilted Lux/Par ------Level Lux/Par --------Level Lux/Par
15” -------- 323/53.0 ----------- 322/52.8 ----------- 341/55.9 ----------- 341/55.9
20” -------- 231/37.9 ----------- 228/37.4 ----------- 242/39.7 ----------- 242/39.7
25” -------- 172/28.2 ------------170/27.9 ----------- 178/29.2------------ 178/29.2
30” ---------132/21.6 ------------132/21.6 ----------- 137/22.5------------ 138/22.6

Sorry, I guess I should have done 10" height but it's just a little harder to get that low and get accurate measurement with this fixture.

So this fixture does better than I thought it would. If I'd known T8 bulbs made that much difference over T12's, I'd have put one in sooner.

Edit: Just to be clear, for converting the lux to Par I'm dividing by 61. Hope that's still correct.

Last edited by sowNreap; 09-04-2012 at 05:01 AM.. Reason: add info
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Old 09-05-2012, 04:11 AM   #5
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Hoppy, I'm a bit confused about the chart because I notice it's not just plotted points with an intersecting line. Yeah ... hadn't taken the time to really look at it before but since I converted the Lux to Par in my post this time it made it easier to see that. LOL

I was trying to see how my 2 bulb T12 white painted compared to your single T8 bulb white painted when I discovered it's not just plotted points. What also adds to my confusion is my T12x2 white painted surface at 20" is approx 45 PAR ... medium to upper medium light. While your single T8 looks to be only 6 PAR. Even if I double the T8 PAR on the chart it's still way, way lower than the "PAR" I got with my T12. What am I missing?

Even though the T8 bulb didn't work correctly in the fixture I did do readings for it. It flickered really, really bad and the light was noticeably dimmer especially after I put the T12 back in. Even with all those problems, the PAR is still higher than it seems it should be for T12 vs T8. Here's those readings for comparison:
15"-- 1300x1 lux / 21.3 par <--- your par from chart approx 15x2=30 .. your higher here
20"-- 901x1 lux / 14.8 par <---yours from chart approx 6x2=12 .. I'm higher but it's close
25"-- 718x1 lux / 11.8 par <-- your par from chart approx 3x2=6 .. I'm way higher here
30"-- 572x1 lux / 9.4 par

So the numbers look closer but still off especially for T12 vs T8. Is it possible your bulb may not have been running at it's full potential? I think you said you used a single bulb in a 4 bulb fixture. My fixture wouldn't run just a single bulb. Or again .. what am I missing?

I sure wish the T8 bulbs would've worked right in my fixture to be able to compare apples to apples. That way we'd have a better idea of what type PAR people can expect with those regular shop lights since they're often used.
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Old 09-05-2012, 05:22 AM   #6
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There certainly are a lot of ways to make mistakes measuring PAR! When I did those T8 readings I borrowed a light from a friend, and put only one bulb in it, because I didn't want to waste the money buying 3 more bulbs. My experience with T8/T12 lights has been that they worked fine with only one bulb instead of either 2 or more bulbs. So, I didn't worry about that part. I did have problems with the light fixture - not all locations would work with the single bulb, so I picked the one that worked the best, no flicker, always started, etc. As I recall, the other positions were reluctant to start, or flickered excessively. Frankly I was more naive then too! I'm not 100% confident in that data, but it was all I had. Now, I suspect that the line on the chart is too low, but I don't know by how much.

Your light has a pretty good reflector, so I'm not surprised that it gives more PAR than I expected. Compare that to the diamond plate, 2 bulb light, to see just how good it is.

I think I may have measured PAR with a 10 gallon tank, with a T8 light too, but I don't have the data, and I'm not that sure I did it - I did a lot of PAR measurements with CFL lights on that tank, so I may have that mixed up in my mind with the T8 light. I do recall that my charted T8 data was consistent with what I though the 10 gallon T8 did for me.

The reason there are no data points on those charts is because I always "smooth" any data like that, sometimes plotting it on log-log paper first to better smooth it, and to better see how the light varies with distance. The charts give you an approximation of what you should get with each type of light, so you have to accept that it is only good to +/-10% at the very best. It isn't possible to get any better result given variations in measuring techniques, variation in bulb ages, manufacturers and reflector cleanliness, variation in ballasts, etc. Also, while 2 foot to 4 foot and longer bulbs give about the same PAR under their center, they don't give exactly the same PAR. Assuming them to give exactly the same PAR just simplifies this.

In the end, if you really want an accurate PAR measurement, you have to measure the PAR you get in your own tank, with water, with typical glass cleanliness, and at the points where you want to know the PAR. This stuff just helps to decide what light fixture is appropriate for what you want to do with the tank.
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Old 09-05-2012, 04:01 PM   #7
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The fixture I was talking about the PAR being so much higher is the white painted surface one with the T12 bulbs not one with the good reflector.

I must be losing my freaking mind!! I have no idea what I was looking at when I thought the chart wasn't smoothed out "plotted points" because now it seems as though it is matching with my numbers. Oops ...
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Old 09-07-2012, 12:38 AM   #8
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So I'm new to the whole light thing and was wondering how much does it affect the plants. Also, how much PAR do you need to grow DHG and other plants. One of my rotalas has taken off while the other not so much. I was also trying to figure out how to reduce the watts I have over the tank to decrease the electric bill without killing my plants. Is that possible with regular floresent light bulbs that would go into a regular socket?
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Old 09-25-2012, 07:25 PM   #9
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I made a mistake in the conversion factor for lux to PAR, using the Mastech lux meter. It is 76 lux per unit PAR, not 61. I corrected the chart of PAR vs distance for T8 lights.

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Old 09-25-2012, 08:32 PM   #10
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Seems to have made a big difference on the polished reflector single bulb fixture ... it's only slightly better than the white painted one now.

I'll have to recheck my setup to see if I'm still good. I may have to low of light the way I have it setup now. At the very least it's going to be more uneven lighting than I thought.
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