The use 0f 18,000k

You don't think making the plants grow tall and spindly is a negative? I don't know that it would have that effect, and I doubt that it would, but if it did, that would certainly seem to be a negative to me. It will make the aquascape look bad, in my opinion.

 

There are no negatives in using the PowerGlo 18,000ks, aside from costing a bit more for being a namebrand bulb. Works about the same as any other bulb.

 

Two reasons why people tend to use 6500-6700k bulbs the most.

1. False belief that they offer the best color spectrum range for plant growth. This has been proven false with PAR measurements. PAR measurements can vary drastically between bulbs with the same K ratings.

2. 6700k offers the most pleasing color for most. Not too white like the 10,000k and not too yellow like the 5000k.

In the end, the k rating means little in terms of plant growth. It is important in determing what may look best to your eyes.

 

I re-read your question and realize I misread it. Sorry

I agree that the appearance of the tank is the primary concern in selecting what bulbs to use. My experience has been that my eyes quickly see almost any bulb as being just right, after a few days at most. The only exception seems to be the red colors. If a bulb is deficient in red light, red plants and fish just never seem to look natural to me. Oddly enough, if I take a photo of a tank that looks the best to me, one with the GE9325K bulb, it looks terrible - almost a purple aquascape. It would be very interesting to see test results where tanks were lighted with only 6700K, only 10,000K, only 18000K, only actinic, etc. just to see if there is any plant growth difference at all. Of course the problem with that is that I doubt that any two 10,000K lights, for example, have identical spectra.

 

I use two Life Glo and one Power Glo 48 in T5's over my 72 gal. Works fine. I also use 2x 18W Aqua Glo T8 over my 10 gal. Looks great. All grows fine.

 

My understanding is that aquatic plant growth is most influenced by the amount of useful light energy that the plants receive in a specified time. The spectrum of the light, per se, is not inportant.

But: photosynthesis occurs when the light is in the 400 to 700 nm range. So called "daylight bulbs" produce light in that range.

Therefore, when measuring light energy in the 400 to 700 nm range, in my opinion, for all practical purposes Lux and PAR are equally useful.

Bill

 

Our eyes are not very sensitive to red light. So, it takes a lot more light in the red area of ths spectrum for us to see it. The lux measurements allow for this, discounting the contribution of red light accordingly. Lights that produce a lot of their intensity in the red part of the spectrum should give relatively higher PAR values than lux values. That tells me that lux and PAR can't be near equivalent except for bulbs producing only a minor part of their light in the red part of the spectrum. But, I could be wrong about this.