# Lux Readings - T8x2 Diamond Plate Fixture

6983 Views 36 Replies 7 Participants Last post by  sowNreap
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EDIT 12/31/2012: For anyone referring to this thread and wanting to calculate the PAR from the Lux readings located through-out this thread use this: In most cases you'll need to add a Zero to the end of the number, then divide it by 76 and add 10% for focusing effect. For example: if the reading is 555, use 5550÷76+10% = 80.3 PAR.

There are a few exceptions where the scale used was only 1x and a zero would not be added, these are usually noted by having 2 numbers like this: 090/905 .. you'd just use the 2nd number without a zero .. par in that case would be 13 .. 905÷76+10%.

Hoping this might make it easier for everyone to use these readings.

I finally received my Mastech Lux meter and bought the T8-2 bulb Diamond Plate fixture and 2 t8 6500k bulbs from Home Depot. The light at the ends of the fixture appears to be darker than in the center. Here's some pics of the fixture showing the reflectors. Sorry about the size.

Bulbs lit but doesn't seem to show as much darkness at the ends as I noticed.

Definitely see another set of bulbs

This angle shows multiple bulbs.

I took readings at various heights, then because I wasn't sure the weight of the cord wasn't tipping the fixture for the first couple heights I re-positioned the fixture and took another set of readings. I didn't just take 2 readings at the same time at the same height. I actually took all the 1st set of readings at the various heights, then went back and re-set the heights again and took new readings so the measurement could be off by 1/16-1/8".

May not be precise since I was in my kitchen using a rod stretched over 2 cabinets, in front of a window and then making use of coat hangars, chains & plant pulleys to achieve the various heights. So it's not the most scientific and someone else may get entirely different readings but as you can see some are pretty close. I did close the blinds and the window has a/c to help block any light coming in. Because of the depth of the cabinets the fixture sat closer to a whitish wall which seems to have added some reflection to the readings. When measuring toward the front my body position would actually change the reading so tried to position myself in the same spot each time.

1st column is 1st set of readings, 2nd column is 2nd set of readings (didn't take a 2nd reading at 10", I can if it's wanted or needed). 3rd column is because I missed 2 readings and since it's night figured I'd take them all for that height again to see how they compared. Plus forgot to do 22" height (which is about where my fixture will hang) in daylight so that is night reading.

Center means at 24" ... right end of fixture is where the hook & chain go which is approx 7-1/8" from the end, not the very end. I may go back a take readings at the end now that I moved my microwave out of the way. LOL Back means toward the wall.

All readings are Lux, I didn't have time yet to convert them yet. And all are from the bulb to the surface of the counter top. I wish I had time to put this into a nice chart or graph .. Sorry!

10" height
Center, center of bulbs --------850
Center, 9" toward back --------397
Center, 9" toward front ------- 278
Center, 12' toward front ------ 172
Right end, center of bulbs -----675
Right end, 9" toward back -----312
Right end, 9" toward front ---- 218
Right end, 12" toward front----130

15" Height
Center, center of bulbs --------544----549
Center, 9" toward back ------- 325----367
Center, 9" toward front ------- 295----278
Center, 12" toward front ------223----211
Right End, center of bulbs ---- 390----394
Right end, 9" toward back ---- 238----238
Right end, 9" toward front ---- 216----202
Right end, 12" toward front -- 162----157

20" height
Center, Center of bulbs ------382----375----396
Center, 9" toward back ------295----295----290
Center, 9" toward front ------237---missed--255
Center, 12' toward front -----195---missed--208
Right end, center of bulbs----290----282----293
Right end, 9" toward back----226----223----220
Right end, 9" toward front--- 180----185----190
Right end, 12" toward front---145----148---156

22' height taken at night only 1 reading
Center, center of bulbs -----------------------345
Center, 9" toward back -----------------------273
Center, 9" toward front -----------------------233
Center, 12" toward front ---------------------196
Right end, center of bulbs --------------------257
Right end, 9" toward back --------------------209
Right end, 9" toward front ------------------- 177
Right end, 12" toward front ------------------147

24" height (not sure why I did 24" meant to do 25" .. oh well, next time)
Center, center of bulbs -------293----298
Center, 9" toward back -------259----247
Center, 9" toward front -------204----209
Center, 12" toward front ------173--- 175
Right end, center of bulbs ---- 223--- 219
Right end, 9" toward back ----196----183
Right end, 9" toward front ----159----157
Right end, 12" toward front ---130----134

30" height
Center, Center of bulbs -------215----213
Center, 9" toward back -------192----193
Center, 9" toward front -------159----169
Center, 12" toward front ------148----149
Right end, center of bulbs ---- 171----170
Right end, 9" toward back ---- 134----152
Right end, 9" toward front ---- 132----132
Right end, 12" toward front -- 115----116

Now that I have them all typed up in columns I may take another set to get a better average. Some readings are really close, while a few are pretty different.

• It feels a bit flimsy. Looks like it should be heavy weight but it's not.
• It appears to have some type of plastic overlay coating which may end up coming off when trying to clean water stains from it
• The reflector is not angled the same all the way across the fixture. Could be somewhat easy to bend into place if needed
• The power cord (5' length) can tip the fixture and needs to be supported
• Looks bright .. I was about blind after I got done taking all those readings. :eek5:
• I like the look of the Diamond Plate
• Fairly cheap. Not as cheap as a regular shop light but this looked so much brighter than those did when I was looking at them in the store.

I also bought a 10-1/2" round brooder clamp-on fixture and will be checking that one in the next few days. They had some EcoSmart 2 pack spiral CFL 27watt (100 watt equivalent) Daylight bulbs marked down for 2.43/pack. Was told they won't be selling the 2 pack anymore only the 4 pack which was \$7.97/4 bulbs. Wish I'd picked up more than I did even though they're 27 watts instead of 23 watts.

Hope this helps. After reviewing Hoppy's T8 chart this fixture doesn't appear to be as good as the white surface fixture ?????
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Are those readings in lux? Does the reading need to be multiplied by 10? (high range on meter) The readings are much too low, but if multiplied by 10 are about what I would expect. I plotted the results and the data look very good, except for possibly being off by a factor of 10

EDIT: It can't be off by a factor of 10 either, more like a factor of 5. If it was off by 10 this light would be giving more PAR than a Hagen GLO two bulb T5HO light, and I find that hard to believe. One thing that would help would be a few measurements with only one bulb installed. Something is wrong here.
Are those readings in lux? Does the reading need to be multiplied by 10? (high range on meter) The readings are much too low, but if multiplied by 10 are about what I would expect. I plotted the results and the data look very good, except for possibly being off by a factor of 10

EDIT: It can't be off by a factor of 10 either, more like a factor of 5. If it was off by 10 this light would be giving more PAR than a Hagen GLO two bulb T5HO light, and I find that hard to believe. One thing that would help would be a few measurements with only one bulb installed. Something is wrong here.
Yes readings are Lux. And after I thought about it I used the 20000 scale (2nd range says x10) so I assume it does need to be multiplied by something.

I'll try the readings with one bulb to see what I get.

Anything else I should do while I'm at it?

EDIT: I tried the reading at x1 lowest scale but it only had a "1" on the display and wouldn't read anything.
Yes readings are Lux. And after I thought about it I used the 20000 scale (2nd range says x10) so I assume it does need to be multiplied by something.

I'll try the readings with one bulb to see what I get.

Anything else I should do while I'm at it?

EDIT: I tried the reading at x1 lowest scale but it only had a "1" on the display and wouldn't read anything.
When the lux is greater than full scale, it just reverts to showing a reading of 1. So, you were on the second scale, which means the readings all need to be multiplied by 10. But, that says this T8 light gives more PAR than the Hagen Glo light.

I notice that you can see two half images of a bulb on each side of both bulbs, so that is at least a fair reflector, while the Hagen Glo has a relatively poor reflector. Now I also wonder if the Hagen light also has an underpowered ballast. I think it is unlikely that your readings are wrong. But, readings with only one bulb will be very interesting too.
When the lux is greater than full scale, it just reverts to showing a reading of 1. So, you were on the second scale, which means the readings all need to be multiplied by 10. But, that says this T8 light gives more PAR than the Hagen Glo light.

I notice that you can see two half images of a bulb on each side of both bulbs, so that is at least a fair reflector, while the Hagen Glo has a relatively poor reflector. Now I also wonder if the Hagen light also has an underpowered ballast. I think it is unlikely that your readings are wrong. But, readings with only one bulb will be very interesting too.
I knew something was wrong when I converted the lux to par and it didn't seem right .. I had forgotten about the scale being 10x.

Yes the reflector seems to decent. As the last photo shows on the right you can see 2 partial bulb images to the right of the bulb, then another image under the bulb and yet another to the left of the bulb.

Got some more readings for you. I added readings taken at the very end of the fixture on the right side. In my 1st post where the chain attaches to the fixture, I called it "right end" now it's called "right/chain. And "right end" is the very end of the fixture. Sorry for any potential confusion.

These were all done at night with the t8 fixture the only light on so these numbers may be more accurate but might be off from the previous readings. I got moving the fixture down pat so can breeze through fairly fast if you want readings taken in daylight again.

1st column is 2 bulbs lit. 2nd column is just 1 bulb lit .. front bulb. All readings used 2nd (10x) scale but in addition where I had to use 1st (1x) scale I gave that reading also. So in the column it will be 10x/1x.

15" height
Center, Center of bulbs--------555 -----371
Center, 9" toward back--------345------256
Center, 9" toward front--------298------151
Center, 12" toward front-------228 -----117
Right/Chain, Center -----------426 ------278
Right/chain, 9" back-----------264 ------196
Right/chain, 9" front-----------219 ------116
Right/chain, 12" front---------173 ------090/905
Right very end, center --------265------176
Right very end, 9" back-------172-------125
Right very end, 9" front ------148 ------075/756
Right very end, 12" front------118------060/601

20" height
Center, Center of bulbs -------401------258
Center, 9" toward back -------308------220
Center, 9" toward front--------253-----125
Center, 12" toward front-------208-----101
Right/chain, center-------------302-----193
Right/chain, 9" back------------233-----172
Right/Chain, 9" front-----------186-----094/965 (probably leaned toward sensor too much when switching scale)
Right/chain, 12" front----------155-----078/783
Right very end, center---------205------130
Right very end, 9" back--------162------117
Right very end, 9" front--------139------069/683
Right very end, 12" front-------116------056/556

22" Height
Center, Center of bulbs---------346-----220
Center, 9" toward back---------288-----202
Center, 9" toward front---------225-----113
Center, 12" toward front------- 191-----094/947
Right/chain, center--------------262-----165
Right/chain, 9" back------------ 218-----154
Right/Chain, 9" front------------171-----086/859
Right/chain, 12" front-----------141-----071/708
Right very end, center----------185-----117
Right very end, 9" back-------- 156-----111
Right very end, 9" front-------- 124-----063/635
Right very end, 12" front-------105-----053/530

24" Height (to compare since I did it before)
Center, Center of bulbs-------- 307-----195
Center, 9" toward back-------- 260-----186
Center, 9" toward front-------- 212-----106
Center, 12" toward front-------182-----087/873
Right/chain, center-------------230-----148
Right/chain, 9" back------------196-----145
Right/Chain, 9" front-----------160-----081/816
Right/chain, 12" front----------137-----068/680
Right very end, center---------169-----108
Right very end, 9" back--------144-----105
Right very end, 9" front------- 120-----060/607
Right very end, 12" front------104-----051/512

25" height
Center, Center of bulbs--------295-----176
Center, 9" toward back--------254-----177
Center, 9" toward front--------207-----104
Center, 12" toward front-------179-----086/859
Right/chain, center-------------224-----131
Right/chain, 9" back-----------195-----136
Right/Chain, 9" front-------- --156-----078/786
Right/chain, 12" front----------135-----065/653
Right very end, center---------164-----096/959
Right very end, 9" back--------143-----102
Right very end, 9" front------- 117-----058/587
Right very end, 12" front------102-----049/495

30' Height
Center, Center of bulbs--------224----- 144
Center, 9" toward back--------195------140
Center, 9" toward front------- 177------097/972
Center, 12" toward front------155------080/804
Right/chain, center------------173------111
Right/chain, 9" back-----------151------110
Right/Chain, 9" front----------138-------075/751
Right/chain, 12" front---------121-------062/625
Right very end, center--------136-------087/875
Right very end, 9" back-------118------ 086/859
Right very end, 9" front-------108------ 059/590
Right very end, 12" front-----095/952--049/494

I was going to do a 2nd set of readings but it got late ... might do it Saturday night if you think it would help. Otherwise I'll move on to the other fixture I bought (the 10-1/2 brooder clamp-on). I'm going to have that Lux meter wore out and out of calibration pretty quick. :red_mouth

Thanks for all your help, Hoppy ... I really appreciate it.

EDIT: wish now I'd added the previous readings into this new post to be able to compare them easier. Maybe I'll come back later and do that.
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To get a general idea of how much a decent reflector improves the situation, could you black it out (black T-shirt or such) and do some basic measuring with one/two bulbs?

My gut feel is that a perfect reflector could roughly double the light intensity. Would be interesting to see some numbers though.
Thank you sowNreap! This is all of the data I need for this light. Here is what it looks like charted on a PAR vs distance basis:

I would never have believed this! That light would need to be suspended about a foot above a 55 gallon tank to drop the intensity enough for a low light tank. Now it looks like the primary reason why T5 lights are so much better than T8 is the reflectors, much more than the brightness of the bulbs. So, a DIY T8 light, using good reflectors could be a very good, cheap way to light 120 gallon and bigger tanks.

The data for the clamp on dome reflector light will be very interesting too.
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To get a general idea of how much a decent reflector improves the situation, could you black it out (black T-shirt or such) and do some basic measuring with one/two bulbs?

My gut feel is that a perfect reflector could roughly double the light intensity. Would be interesting to see some numbers though.
I'll see what I can do late tonight. It would be interesting to see the results.

And after I take down my aluminum foil lined 2xT12 shop light I might do readings for that just to see what effect the foil has. Then take the foil off and do another reading just too see how it compares. But those 2 may have to wait a bit. I'm going to get readings on the brooder light first since I wanted to use that on my 10 gal grow-out tank. And it may be more beneficial to everyone .. as long as Hoppy doesn't mind me imposing upon him to make more charts. :biggrin:

{snipped ....}
I would never have believed this! That light would need to be suspended about a foot above a 55 gallon tank to drop the intensity enough for a low light tank. Now it looks like the primary reason why T5 lights are so much better than T8 is the reflectors, much more than the brightness of the bulbs. So, a DIY T8 light, using good reflectors could be a very good, cheap way to light 120 gallon and bigger tanks.

The data for the clamp on dome reflector light will be very interesting too.
Thanks very much for the chart Hoppy!! I haven't had time to do the calculations. But my oh goodness .. I didn't think it would be THAT good! Thought I'd would need 2 of these fixtures for my tank but now looks like 1 is almost too much.

That almost complicates things more than I wanted. LOL I've got 2 sets of ceiling hooks for 2 light fixtures so they aren't centered over the tank. Now I'll have to figure out how to hang it or guess I'll just have to put more holes in the ceiling.

If I gave you another reading for a single bulb could you chart that also? Does it hurt this type fixture to run them with just 1 bulb? I haven't looked at the numbers in detail and I assume one bulb probably won't give good coverage for a wider tank but just curious to see how it compares.

This forum has created a monster!! I want to test everything now. Especially since that I have that great spot for hanging the fixture and have it all measured off and fixed up. And I hope it may help others.. sort of paying forward a bit for the help that everyone has given me.
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It is no imposition on me to do those charts. I enjoy doing that, so I do them for fun anyway. And the more different light fixtures we can get PAR data on the better it will be for everyone.

About the diamond plate light: are the reflectors aluminum, stainless steel, or what? You mentioned how light the fixture is, which makes me think they might be aluminum. And, did you ever figure out if they are plastic coated?

If you were to tape some sheets of black paper together to make a 4 foot long piece, then use that to block the light from hitting the reflector, PAR data from that would be a bare bulb with no reflector. That would tell us how much effect the reflector has.

I'm puzzled by the fact that the PAR for two bulbs is about 1.5-1.6 times the PAR for one bulb. I can't see why that would happen and why the ratio isn't 2 to one. Was the sensor centered under the one bulb or still centered under the middle of the light? Or was the sensor always under just one bulb? The latter might make the ratio 1.5 instead of 2.
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I'll check the fixture again and post back but think it's aluminum.I'll examine more thoroughly to see if it does have plastic coating. I didn't notice it or couldn't tell when doing the measurements.

I don't have any black paper that I can think of. I do have a couple 2' long black towels I thought about trying to use. I'll have to scrounge around and see what I have available to "blackout" the reflector.

When I took readings it was always the center of the fixture even when I did single bulb. I moved the sensor forward debating whether I should do center of bulb and the lux went down, so that could be why that is off. Sorry. I already had the marks on the countertop for center of fixture so just went with that. I can measure off center of bulb and re-do if you want to get more accurate reading.
If you just get 3 readings with the sensor centered under the "on" bulb that might tell us something. (I'm not sure what it will mean, yet.)

White thick paper would also work well to block off the reflector. That would simulate a normal T8 fixture with white painted background. The paper could just lay on the bulb.
Would cardboard work? I have all kinds of boxes I could tear up. I thought about black trash bag but it seems too shiny. Oh .. thought of something. The black weed block cloth .. I'll have to see how transparent it is and how big the holes are. Might allow to much light through since designed to allow water to penetrate.

Not sure I have any thick white paper, only printing paper but it appears to transparent. So no pure white or pure black that I've found yet ... but I'm still looking.

I'll take a few readings centered under single bulb. I assume you mean at different heights ??? Or 3 readings same height???
Cardboard would work great - pretty bad reflector.
I actually found some black felt material. Held up to light, no penetration. Perfect. I knew if looked long enough I'd find the ideal thing. I come from a family that hardly ever throws anything away. LOL

Glad though that the cardboard would work. Just in case.
Three readings at different distances, not all at the same distance. And, I only use the center reading, except for curiosity about how uniform the light is over the whole substrate.
Lots of good work, here, sowNreap!

I see a couple of interesting things in some of these readings.
When you were doing the 'one bulb' series, you said you were using the bulb at the front.
Looking at the results, it looks pretty consistent that the readings taken at the back of the tank are almost always brighter than the readings taken at the equivalent location, but front.
Theory: The closer you are to centered under the bulb the more restrike you are losing. Light that goes straight up from the bulb reflects straight back down and is re-absorbed into the bulb. When you are taking readings away from right under the bulb the reflection is more varied and you are seeing more of the reflected light because it is somehow reflected around the bulb. The diamond pattern is scattering the light.

When you are too close to the surface (see first post with the charts, 10" test results) the maximum is a really large maximum right under the center of the fixture. Much higher light than all other locations.
But when you raise the fixture the readings sort of even out. The middle-center is still higher, but not as extreme as the 10" above the counter test. The higher you go the more even the light intensity over the whole tank.

Translating these ideas to an aquarium: The best reflector will not be a flat sheet, but should have some way of directing the light that starts off heading away from the tank so that light enters the tank. A parabolic reflector with some special 'bumps' directly over the bulb can do this.
The higher you can place the fixture the more even the light will be. If you want a high intensity spot, then lower the fixture.
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Thanks Diana. I'm not real sure but think the wall is causing it to be brighter in back. ??? I now wish I'd hung that black cloth on the wall to see what effect that had on the readings. Maybe next time. I also noticed the higher the fixture the more even the light was.

Hoppy, it does appear that what makes the fixture so shiny is a thin foil type coating. Maybe some type of a chrome plating process. ??? I was able to peel about a 4mmx8mm corner up. It stuck back down really good as I had a hard time peeling it back up again. But I'll probably glue it to keep it from tearing. Here's a photo showing that. Used super macro about 2" away and then cropped heavily.

The plastic I first noticed is clear like what the fixture was packaged in and is stuck to the rivets and screws. Here's a pic of that. Again super macro about 1" away and cropped. The rounded black thing is a reflection of the camera lens to give some perspective.

Here's a photo of the fixture with the black felt type cloth I used to block the reflector:

Hoppy I didn't see your reply so I took most of the same readings as before. I eliminated the reading taken where the chain hangs and just did the very end. Since I took them, I'm including them here. Keep in mind this is not scientific quality measurements I'm doing the best I can with what I have to work with so I could be off as much as 1/8". I need a better more accurate way of measuring.

1st column is blacked out reflector with 2 bulbs lit. The 2nd column is not blacked out but with only 1 bulb lit reading from the center of front BULB not center of fixture. As before, all readings used 10x scale but in addition where I had to use 1x I gave that reading also. So in the column it will be 10x/1x

15 Height ...............................................Blacked Out ... 1 bulb ....... middle between both bulbs to show difference
Center of fixture, Center of single BULB -------- 213--------------282--------323
Center of fixture, 9" back -------------------------176-------------259
Center of fixture, 9" front ------------------------146--------------133
Center of fixture, 12" front -----------------------113---------------114
End of fixture, Center of BULB -------------------092/919----------119--------139
End of fixture, 9" back----------------------------078/786----------124
End of fixture, 9" front----------------------------068/685--------063/629
End of fixture, 12" front--------------------------057/575--------054/542

20" Height
Center of fixture, Center of single BULB --------150-------------227---------239
Center of fixture, 9" back------------------------134-------------204
Center of fixture, 9" front------------------------118-------------115
Center of fixture, 12" front----------------------100-------------091/909
End of fixture, Center of BULB------------------073/734--------111----------119
End of fixture, 9" back----------------------------066/664-------106
End of fixture, 9" front---------------------------060/601--------061/608
End of fixture, 12" front--------------------------054/541--------049/489

25" height
Center of fixture, Center of single BULB ------113---------------168----------174
Center of fixture, 9" back-----------------------105---------------161
Center of fixture, 9" front-----------------------095/954---------104
Center of fixture, 12" front---------------------085/849---------079/789
End of fixture, Center of BULB-----------------062/617---------090/899------094/942
End of fixture, 9" back--------------------------057/570---------089/891
End of fixture, 9" front--------------------------052/526----------055/555
End of fixture, 12" front-------------------------048/485----------044/445

30" height
Center of fixture, Center of single BULB-------088/881----------130----------134
Center of fixture, 9" back-----------------------085/849----------130
Center of fixture, 9" front-----------------------077/775----------091/910
Center of fixture, 12" front---------------------071/709-----------070/700
End of fixture, Center of BULB-----------------051/515-----------077/774-----078/782
End of fixture, 9" back--------------------------049/490-----------077/775
End of fixture, 9" front--------------------------046/460------------052/524
End of fixture, 12" front-------------------------043/430-----------042/420

Sorry the columns are off a bit. Can't get them lined up all nice & purdy. LOL

What I find interesting is how close some of the readings are for the blacked out 2 bulbs VS non blacked out single bulb.
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I charted these data points, center of the tank only, using the blacked out 2 bulb, and the one bulb with reflector readings:

I interpret this to show that a good \_/ shaped reflector increases the PAR from the bulbs by little more than 100% - it roughly doubles it. This is what I found with a similar shaped DIY reflector and a horizontal screw-in CFL bulb. But, this also suggests that even T8 lights can have substandard ballasts. The T8 aquarium light I tested, which had white plastic flat surfaces behind the bulb, no real reflector, gave significantly less PAR than this one does. I know that light was fairly old, but I thought it did have an electronic ballast. The light was sometimes reluctant to light up, so it might have had a simple inductor ballast. If it didn't have an electronic ballast, this difference may be the effect of using an electronic ballast in the diamond plate light.
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Thanks a lot sNr for the measurements, and Hoppy for the graphing expertise. Confirms what I suspected. Using good reflectors is a huge factor!
Thanks Hoppy for the new chart. It's really an eye-opener and very helpful. I know you only use the center for these charts but now realize how much lower the light at the ends are so I can make sure to plant any higher light plants more toward center (which I usually try to do but measuring the end really shows it).

Now I'll need to figure out how best to utilize it to achieve high-low light or low-medium light without having the plants grow toward the light if using 1 bulb. For right now think I'll just hang it higher until I figure out how I want to do it since I have several options. Now I can get rid of the 3x40watt bulbs and use 1 or 2 - 32 watt and cut electricity usage a little bit .. hey every little bit helps.

The fixture I'll be replacing is a very old T12 white painted plant grow light. I'm going to test it to see how it compares with Hoppy's old T8. I don't know what kind of ballast is in it.

Now on to testing the 10-1/2 clamp-on light.

EDIT: Thanks Hoppy .. I see you added the chart to the Par vs distance thread. That might help people find it easier.
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