Quote:
Originally Posted by Myka
I don't think this is accurate. I'm actually going to take a closer look at PAR levels in the ole MH/T5 debate, but I'm pretty sure that comparing W to W you need a bit less T5 to get the same intensity as the MH. One 250w MH over a 24x24x24" I think would be far less PAR than twelve 39w T5s. I can't even imagine how bright twelve T5s would be over that space!!! I actually don't think it would fit.
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actually, it is very accurate, I took my PAR meter down to Safari pets and did a direct comparison between PC/T5/MH the 250 watt MH still had almost twice the PAR at twice the distance, and yes it was high output T5. I will say though that the T5 impressed me enough for me to buy one and put it on my fresh water planted tank as it had 40% more output as the same size of PC.
If you do a search on "watt per gallon" you are going to see a lot of rants from me about it as it is a totally useless measurement and or comparison that in no way relates to anything except the exact same type of lighting at the exact same color temp on the exact same dimension tank.
I usually ignore this but there is a lot of people using this lately that are fairly new to the board, so I will explain it again for there benefit.
first some preamble.
no matter how many lights you add you will not increase the intensity of the light
unless you go to a different type of lighting. what you will do is spread the same intensity level over a larger area and create a more even lighting.
Intensity of the light is its penetrating power at a specific distance. When we measure PAR we are measuring the intensity not the total amount, because the total amount means nothing unless it has the power to punch down to the depth you need.
this is why you can grow SPS under NO lights in very shallow tanks, but you can't in deeper tanks.
so on to watt/gal
lets say we have a 100 watt light bulb on a 33 gal tank, thats 3.03 watt per gal, right
so lets look at a classic 33 gal tank 18" tall, then look at my 33 gal tank it is 22.5" tall, and finally lets look at a tank that is 36" tall, 18" wide and 12" front to back (tall 33) they all have the same "watt/gal, but do you think you could grow SPS at the bottom of the 36" tall one? but now if we upgraded from 100 watts of NO to 100 watts of T5 we could maybe get something in the middle tank if we did put it to deep, but still the last example would take more punch.
Which is where MH come in.. the intensity of a MH is not matched by tubs in any way. The MH can penetrate farther down, which is what really matters to us. Do you necessarily need this power, no, but you might
If you want to keep high light corals on the middle of your tank then yes T5's will be good, but if you want to keep some on the bottom of your tank, you will be better off with MH.
take an example from the planted fresh water tank forums, they start out with shop lights and low light plants, then they add better lights (T8's) and find they need CO2. so they get plants that are higher light plants and find light is the limiting factor, so they upgrade to VHO/PC/T5's and use more CO2. but for the deeper tanks T5 HO's arn't even enough when you add CO2 as light becomes the limiting factor again, then they add MH and growth explodes again which shows that a MH will deliver more PAR at depth than T5's. the question remains though... how much punch do you need. Personally I do not think T5's are a long term solution for deep tank in any way other than color supplement. I have the T5's on my fresh water tank (22" deep) and my carpet plants are growing at about 1/2 the speed that they are in the pet shop on a 24" deep tank running MH.
Steve