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Light question

888 views 6 replies 3 participants last post by  Z81 
#1 ·
I have a 40 gallon breeder I want to grow plants in, haven't decided which type of plants yet but think I want at least medium light. I've built a canopy that houses 3 or 4 8" aluminum reflectors (vertical) with 6500k 23 watt CFL spiral bulbs. They are 18 inches from the substrate, I also have a DIY co2 reactor with a pump diffuser. So my question is this considered low medium or high?
 
#2 ·
Hi Z81,

My guess is that you'll be in the higher end of low light, verging into medium. A single vertical 23W CFL in an 8" aluminum reflector at a distance of 17 inches from the substrate will give you around 45-50 PAR. This is over an area of 10 x 10 inches. I have measured this. You do not get the same PAR value if the bulb is horizontal in a 6" reflector, the PAR is lower.

If you reduce the light distance to 13 inches from the substrate, you'll get about 120 PAR over that 10x10 inch area which would be well into med/high light.

To extrapolate this to your tank situation, you have to see how much area each of your bulbs is covering. I'm guessing its a bit more than 10x10 inches. But, also, you're going to have some overlap as the light from each bulb spills into its adjacent areas.

I would suggest that you have a 23 watt bulb for each 12x12 inch area of your tank footprint. I would then set the lights at a distance of 15 inches from the substrate (if possible). This might put you into the 50-60 PAR range, which is a great PAR range to be in with or without CO2.

My original measurement of the vertical 23 watt bulb in an 8inch reflector is not a guess, but my extrapolation to your tank is...

Cheers,
 
#3 ·
From the most recent PAR measurements I have seen with a 23 watt soft white CFL bulb in a 8.5 inch diameter reflector you should have about 35 micromols of PAR at 18 inches. That is good low light and with DIY CO2 you can grow a lot of different plants very well. You could use 4 of those reflectors to try to get uniform lighting, but the problem will be with the 18 inch front to back depth of a 40B tank. I don't see how one of those reflectors can cover an 18 inch wide area anywhere near uniformly. So, maybe you need 8 of them! It starts to be something other than cheap when it takes that many bulbs and reflectors. Also, those will add a lot of heat to the water too unless there is an inch or more gap between the end of the reflector and the water, and 8 of them in an enclosed canopy might mean you need a cooling fan.
 
#5 ·
From the most recent PAR measurements I have seen with a 23 watt soft white CFL bulb in a 8.5 inch diameter reflector you should have about 35 micromols of PAR at 18 inches.
You get higher readings when the measurement is taken in a tank filled with water. Do you know how those readings were taken? Did you take them yourself?

Also on your "Lighting with PAR instead of Watts" post, I notice that you also report "dry" PAR readings. I think that this can be misleading since you get a significant boost in PAR due to the combined effect of the glass and water.

My personal preference is to measure as closely as possible to the configuration in which the plants will be growing; i.e. in a tank filled with water. But I suppose some reading are taken dry due to the face that they may not have a waterproof sensor.

Just curious. But at the same time, my reading was taken at 17" and the one you reported at 18". And mine was taken in a smaller tank, so maybe there was more light focusing effects.

Cheers,
 
#4 ·
Just the two I was hoping for responses from thanks. Hoppy mentioned soft white bulbs these were labeled daylight bulbs not sure if that made a difference or not, also I get good light coverage with 3 by spreading them out using the clamps they came with. I'll drop the lights a few inches and put the 4th back in and call it a day I think :)

Been happy with the experiment of CFL so far considering this is my first real tank. I'm posting a picture of my tank from a few weeks ago it had been stocked for maybe a month (was already cycled) at this point all the plants were very small when I added them. The Anacharis was very narrow and spread out when I first got it you can see in the picture there. It is almost like it grows too fast it grows a few inches a day I've cut tons of it and tossed out. I plan to replace it with a different plant maybe water sprite.
 

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#6 ·
I'll drop the lights a few inches and put the 4th back in and call it a day I think..
Yeah, I think you'll be safe - Granted we are doing a lot of extrapolating. But even if you end up with more light than expected, you are supplementing with CO2 so it shouldn't be a problem as long as you are also dosing nutrients. In higher light, your plants will just grow that much faster.

Speaking of which, nice pic. But I would put a LOT more plants :)

Lots more.

Cheers,
 
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