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Discussion Starter · #1 ·
I now have a 36 watt, single bulb AHS light on a small riparium, with a 10000K bulb in it, and I have our plant club's PAR meter for awhile. So, I took some measurements of the light intensity today. I also have data from a single 55 watt AHS light, with a GE9325K bulb. The 36 watt light has been in use daily for about 2 months and the GE bulb had been in use about a year when I took the data. I believe that makes the bulbs approximately equally aged, since we know that the first month or so the bulb dims more than in the next year, then apparently dims more rapidly over the 2nd year - not certain about that last part.

I plotted the data I have, first to verify my belief that PC bulbs give the same intensity at a given distance, no matter what wattage they are, for comparable fixtures/reflectors being used. I now believe that even more firmly. I also don't believe that there is much intensity difference between bulbs of different K ratings or different vendors, with PC bulbs of this type - linear pattern contacts.

Here is the graph of the results:


This can be used to get an idea about how much light you will get with any height tank, or any distance between the substrate (or light sensor) and the bulbs. Note that a single bulb is only usable, for a low light tank, for tanks up to 24 inches high, or for high light for tanks up to about 12 inches height. Two bulbs/reflectors side by side approximately doubles the intensity.
 

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Interesting. ( I have a 55 wat AHS fixture)

Do you have any comparisons to a T5 fixture? Lot's of discussion on which is better but I have not seen any direct comparisons.

Thanks for this post

Bill
 

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Discussion Starter · #3 ·
Interesting. ( I have a 55 wat AHS fixture)

Do you have any comparisons to a T5 fixture? Lot's of discussion on which is better but I have not seen any direct comparisons.

Thanks for this post

Bill
Thats a good question. Here is a plot of the intensity vs distance for a single T5HO bulb and an AH Supply one bulb light. Note that the intensity vs distance is essentially the same, but the T5HO light covers about twice the tank area as the AHS light. So, it takes about twice the wattage of AHS light to light a given tank size as it takes for a T5HO light.
 

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You can see from the graphs, that the drop off still provides good lighting even at 24" deep aquariums.

Few plant hobbyist have tanks deeper than this, so PC/T5's etc are fine and can grow most anything even at deep depths.

Regards,
Tom Barr
 

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it takes about twice the wattage of AHS light to light a given tank size as it takes for a T5HO light.
Wow. So according to this, T5 bulbs are about (or a little more than) twice as efficient as PC bulbs? :icon_eek:

I would have expected the PC bulb to provide significantly more light at a given spot, since it is basically two T5 bulbs side by side.
 

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I believe that makes the bulbs approximately equally aged, since we know that the first month or so the bulb dims more than in the next year, then apparently dims more rapidly over the 2nd year - not certain about that last part.
This is correct for lights. There are organics inside the bulb, and when you turn the light on UV strikes the organics, breaks the bonds around the carbon, and leaves carbon deposits on your glass. This all finishes pretty quickly, probably more like 2 weeks to see 90% of the total degradation. Then your bulb hardly degrades at all, but it's hard to say for how long because it depends on the bulb. Eventually, because the seal isn't perfect, and it's gone through however many thermal cycles, it starts to leak. The size of that leak affects how long the downward slide goes. A corroded contact would greatly accelerate this.
 

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Discussion Starter · #11 ·
A very nice thread. Thanks!
Would like to ask for clarification. Looking at the drop of intensity over distance, I am assuming this is done under water and the distance in your graph represents depth of water. Am I correct?
The data is a mix of under water and in air. As far as I can tell there is no significant difference in the drop. It isn't due to absorption of the light by the water - it takes about 10X more water than we ever use to cause a significant absorption of light - it is from the geometry. The further the light from a source travels, the bigger the area of the "beam", and it has to be a drop off that is roughly proportional to one over the square of the distance traveled. It is only rough because as you get further from the bulb, the finite length of the bulb has a greater and greater effect, and because there is some reflection of light from the glass sides. The closer you get to the bulb the more the inverse square relationship breaks down - that is why the PC bulb data flattens out at small distances.

I have checked repeatedly looking for a difference in intensity with the light going mostly through the water and the light going entirely through the air. I can't find that difference.
 

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Discussion Starter · #12 ·
Wow. So according to this, T5 bulbs are about (or a little more than) twice as efficient as PC bulbs? :icon_eek:

I would have expected the PC bulb to provide significantly more light at a given spot, since it is basically two T5 bulbs side by side.
A PC bulb is roughly two T5NO bulbs side by side, not T5HO - I think. A 55 watt PC bulb is about 22 inches long, two 27.5 watt 22 inch single tubes. Put them in one long row, instead of side by side, and you have a 55 watt T5 bulb, but producing about half the light as a T5HO bulb of that length. (I admit I get a bit confused trying to sort this out.)
 

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A PC bulb is roughly two T5NO bulbs side by side, not T5HO - I think. A 55 watt PC bulb is about 22 inches long, two 27.5 watt 22 inch single tubes. Put them in one long row, instead of side by side, and you have a 55 watt T5 bulb, but producing about half the light as a T5HO bulb of that length. (I admit I get a bit confused trying to sort this out.)
I think you are mistaken.

It's wattage per length... so a T5HO burns 54W/45in, and a PC 55W/22.5in/2. PC is just a bent T5HO bulb (in that wattage).

The PC bulb should produce more light than the T5 bulb. Not twice, but noticeably more. Perhaps you compared one that did not produce much PAR vs one that didn't.
 

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Discussion Starter · #14 ·
I think you are mistaken.

It's wattage per length... so a T5HO burns 54W/45in, and a PC 55W/22.5in/2. PC is just a bent T5HO bulb (in that wattage).

The PC bulb should produce more light than the T5 bulb. Not twice, but noticeably more. Perhaps you compared one that did not produce much PAR vs one that didn't.
As I said, I do get confused by this. You are right that wattage and lengthwise, a 55 watt PC and 54 watt T5HO seem to be identical. But, no question, the T5HO produces more light. Just looking at the lit up bulbs demonstrates that - I can stare at the PC, but it is painful to try that with a T5HO. The reasons for this are beyond what my knowledge can explain. Everything I think might be the reason is easily proven to be false. I'm ready to attribute it to magic:biggrin:
 

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The data is a mix of under water and in air. As far as I can tell there is no significant difference in the drop. It isn't due to absorption of the light by the water - it takes about 10X more water than we ever use to cause a significant absorption of light -
Don't say that, what about the myth?
Who's going to keep it(the myth) alive?
Folks have long said this rubbish, they cannot be all wrong can they?:hihi:

I have checked repeatedly looking for a difference in intensity with the light going mostly through the water and the light going entirely through the air. I can't find that difference.
I could not either using the LiCOR 193 sensor matched with this same Apogee going from 0 cm to 200 cm every 20 cm using a matched pair on pvc pipe.

So at the depths we generally use, and deal with, most of that stuff often said, including blue light absorption I'd speculate, is myth.

I'll look into that part later.

Regards,
Tom Barr
 

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As I said, I do get confused by this. You are right that wattage and lengthwise, a 55 watt PC and 54 watt T5HO seem to be identical. But, no question, the T5HO produces more light. Just looking at the lit up bulbs demonstrates that - I can stare at the PC, but it is painful to try that with a T5HO. The reasons for this are beyond what my knowledge can explain. Everything I think might be the reason is easily proven to be false. I'm ready to attribute it to magic:biggrin:
Could be the ballast too... it's what drives the bulbs to a certain wattage.
 

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Hmm how interesting. Hoppy, have you tested what the intensity is like with a reflector attached? In your first post you said it approximately doubles the intensity. Can you post a chart with the bulb data and then bulb + reflector data for comparison?

How did you determine what PAR rating equates to High - Medium - Low light conditions?

Also, where did you get the PAR meter from? I'd like to buy one too.
 

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Discussion Starter · #19 ·
Would be curious to see the plot of new bulbs overlayed with the olde ones you tested. Would be great to truly see how much of a drop off there can be in PC bulbs.
Several months ago someone posted their PAR readings for a series of 55 watt PC bulbs with varying times in service. I plotted it at that time, and I think I posted it on a forum, but possibly not here. I found this yesterday while looking for something else. I'm not sure what distance the sensor was from the light bulbs for this data, but it was obviously very close.
 

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Discussion Starter · #20 ·
Hmm how interesting. Hoppy, have you tested what the intensity is like with a reflector attached? In your first post you said it approximately doubles the intensity. Can you post a chart with the bulb data and then bulb + reflector data for comparison?

How did you determine what PAR rating equates to High - Medium - Low light conditions?

Also, where did you get the PAR meter from? I'd like to buy one too.
My local plant club, Sacramento Aquatic Plants Society, with a lot of help from Tom Barr, purchased one several months ago. I borrow it from the club when I have a desire to do some more measurements.

Tom Barr suggested the ranges for low to high light intensity, and they pretty well correlate to what I have seen in my tank.

The data I posted is all with light fixtures which include the reflectors. The T5 data came from someone else who spent the effort to measure PAR intensities for a lot of fixtures from different manufacturers, with different numbers of bulbs and lengths of bulbs. I have been massaging that data since I got it. The PC data is from my AH Supply 55 watt kit, which, of course includes the reflector.

The statement about the effect of the reflectors comes from various sources, where people claim from 1.5 to 2.5X improvement from using the reflector. I have no way to verify that claim, although I could do it for my 36 watt PC bulb, and now that I am thinking about it, I think I will do so. (That's the trouble with posting this stuff, there is always another very interesting test that can be done!)
 
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