Nope didn't take it that way at all. Besides there isn't anything wrong with challenging something you think may be wrong anyway. 
I don't happen to have any solid numbers laying around anywhere but I bet all the data needed is already available on Sanjay's site.
There WILL be a difference but it's not what many uninformed people think it will be. By this I mean most people (guessing) will think 2 times the watts = 2 times the available light and it's not like that as already mentioned.
Let's try taking a step back and asking the question, why do you need so much light in the first place? Are you attempting to build out an all SPS tank that will have SPS growing basically at the bottom of the tank to the top? Do you plan on having lower light corals also? How will you acclimate the corals to the new light? The question I beg to ask is why do you need such high wattage lamps? I just want to make sure you don't fall into the camp that thinks if 250 is good then 400 must be better! Cause it ain't so for the "average" reefer. If you really have the need then sure get them but don't just get them because you "think" it's better without knowing all the downsides also.
As an example, read what mr_X posted about his observations with 400 watters and LPS. This is a personal opinion but it's also shared by a lot of other experts in the field and that is, there is way too much emphasis put on high wattage lights. MOST corals don't want or NEED high wattage halides and WILL ACTUALLY do better in our tanks under typical tube (T5/T8/T12) wattages which are normally lower then halide setups. Very few tanks actually need as much light as we put on them and many would do better with less light but a more "full" spectrum (mixed lamps). I know this is going to open a can of worms.
A pretty decent book that talks about a lot of this is Anthony Calfo's book of "Coral Propagation" which was just released in December (new version). He goes into different light setups and requirements for optimal growth of different types of corals for growing/propagating and also goes into greenhouses and setups. He's probably/arguably the leading author on the subject of propagating corals. There surely are many other experts in the field but he has written and shared his views instead of garding them as if they were a trade secret.
Think about this. Gigas clams will grow very well sitting on the bottom of a 30" tank with 175 or 250 watt halides. Most SPS will grow fine under VHO T12s if kept in the top 1/2 of a tank. Now when you think on these lines why consider 400s unless you're talking about a 36" depth tank or something similar? If so you'll have so much light that anything but the most light loving corals are going to suffer big time. Why not use lower wattage lamps and be able to stock many different types of corals and avoid having to run a chiller?
If you're starting over or looking to build your lights for the first time what about going with multiple T5 lamps and maybe leave room for a couple of 150 halides if needed in a few places for higher light loving corals? <--- Just a thought/suggestion.
Remember light is probably a distant third/fourth for most corals on their list of needs. Clean water (much cleaner then most people think) which are poor in dissolved inorganic nutrients (ammonia, nitrites, nitrates, phosphates) but are very rich in organic nutrients (zooplankton, phytoplankton, detritus, algae, bacteria, etc).
Good flow suitable for the species in the tank and to keep detritus from settling and for helping the corals to not have any stagnant water near them. Then light. Remember there is a lot more to calcification of corals then light. Simple things like keeping the phosphates and nitrates very low (zero by test kits and with no nuisance algae in the tank) in the tank will contribute more to the corals health then your lights will. Any elevated nitrogen (ie nitrates) or phosphates hinder calcification. I think a lot of people erroneously try and make up for other bad parameters by using stronger lights then needed which can work but isn't optimal and just costs them extra money on their electric bill and also causes other issues (nuisance algae, problems with lower light loving corals, etc)...
Carlo
PS I know this post touches a lot of different things and many could be argued to death, but the main point is to see if there is really a need at all for higher then "normal" lighting.
PPS Feel free to start a new thread with any info you disagree with.
I don't happen to have any solid numbers laying around anywhere but I bet all the data needed is already available on Sanjay's site.
There WILL be a difference but it's not what many uninformed people think it will be. By this I mean most people (guessing) will think 2 times the watts = 2 times the available light and it's not like that as already mentioned.
Let's try taking a step back and asking the question, why do you need so much light in the first place? Are you attempting to build out an all SPS tank that will have SPS growing basically at the bottom of the tank to the top? Do you plan on having lower light corals also? How will you acclimate the corals to the new light? The question I beg to ask is why do you need such high wattage lamps? I just want to make sure you don't fall into the camp that thinks if 250 is good then 400 must be better! Cause it ain't so for the "average" reefer. If you really have the need then sure get them but don't just get them because you "think" it's better without knowing all the downsides also.
As an example, read what mr_X posted about his observations with 400 watters and LPS. This is a personal opinion but it's also shared by a lot of other experts in the field and that is, there is way too much emphasis put on high wattage lights. MOST corals don't want or NEED high wattage halides and WILL ACTUALLY do better in our tanks under typical tube (T5/T8/T12) wattages which are normally lower then halide setups. Very few tanks actually need as much light as we put on them and many would do better with less light but a more "full" spectrum (mixed lamps). I know this is going to open a can of worms.
A pretty decent book that talks about a lot of this is Anthony Calfo's book of "Coral Propagation" which was just released in December (new version). He goes into different light setups and requirements for optimal growth of different types of corals for growing/propagating and also goes into greenhouses and setups. He's probably/arguably the leading author on the subject of propagating corals. There surely are many other experts in the field but he has written and shared his views instead of garding them as if they were a trade secret.
Think about this. Gigas clams will grow very well sitting on the bottom of a 30" tank with 175 or 250 watt halides. Most SPS will grow fine under VHO T12s if kept in the top 1/2 of a tank. Now when you think on these lines why consider 400s unless you're talking about a 36" depth tank or something similar? If so you'll have so much light that anything but the most light loving corals are going to suffer big time. Why not use lower wattage lamps and be able to stock many different types of corals and avoid having to run a chiller?
If you're starting over or looking to build your lights for the first time what about going with multiple T5 lamps and maybe leave room for a couple of 150 halides if needed in a few places for higher light loving corals? <--- Just a thought/suggestion.
Remember light is probably a distant third/fourth for most corals on their list of needs. Clean water (much cleaner then most people think) which are poor in dissolved inorganic nutrients (ammonia, nitrites, nitrates, phosphates) but are very rich in organic nutrients (zooplankton, phytoplankton, detritus, algae, bacteria, etc).
Good flow suitable for the species in the tank and to keep detritus from settling and for helping the corals to not have any stagnant water near them. Then light. Remember there is a lot more to calcification of corals then light. Simple things like keeping the phosphates and nitrates very low (zero by test kits and with no nuisance algae in the tank) in the tank will contribute more to the corals health then your lights will. Any elevated nitrogen (ie nitrates) or phosphates hinder calcification. I think a lot of people erroneously try and make up for other bad parameters by using stronger lights then needed which can work but isn't optimal and just costs them extra money on their electric bill and also causes other issues (nuisance algae, problems with lower light loving corals, etc)...
Carlo
PS I know this post touches a lot of different things and many could be argued to death, but the main point is to see if there is really a need at all for higher then "normal" lighting.
PPS Feel free to start a new thread with any info you disagree with.
