What is the equivalent in LED to 400w MH?

Also just another thought, as you mentioned a 250MH. A 400w 20000K mh would tend to have similar PAR to a 250w 10000K. However, blue LEDs don't waste emery in the UV range, so tend to have more PAR. So, if your comparing blue LEDs to blue MHs, the LEDs likely do have a bigger advantage, as you are essentially reducing the scope of the compared spectral range, to the LEDs advantage.

However, those parameters should be defined when making a specific statement...


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I know they said you can not just have a white cannon, you also have to have a blue one to complete the spectrum.
The thing is, can you have a 100 watt white cannon and a 50 watt blue cannon since the blue requires less power to be equal in par?

 

Presumably they are talking about a visual effect, and suggesting that the mix would look better to your eye. The human eye is tremendously less sensitive to blue than green-yellow. So, likely you would have better results actually using a 50W white and 100W at least visually, if you want more of a blue-white coloration that is.

What would be better for your corals, I couldn't say as there is not much published data on coral spectral responses. So, generally a mix of light is preferable, so then maybe a 100W white and 50w blue would be better, but that's just a guess.

As to the human eye, from wikipedia, (Luminosity function - Wikipedia, the free encyclopedia) here is the Photopic Luminosity function used to weight lumens to match the sensitivity of the human eye. It is heavily weighted towards yellow-green, which is why we don't use lumens for reef lighting.

(Note: it's the black line and 400ish is blue and 600ish is red, the peak is green-yellow range)

 

Sorry, just re-read your comment. The blue-dosn't require "less power to be equal in par". With an led, a blue LED should be about the same PAR as a white LED, although there could be some variation. Did you get that from me or someone else. If me, then I think I confused you. A blue MH is generally less PAR than a white MH. However, a blue LED tends to be similar par to a white LED. So, when comparing a blue led to a blue MH, they blue LED tends to have an advantage. However, if you are comparing a white LED to a white MH, then there should be less of an advantage.

 

It is to bad we cant borrow or rent these lights for a few months to find out what is best.

 

Others sometimes are able to do so though and publish the result.

Here is a good example,

Feature Article: Quantitative Comparison of Lighting Technologies: Metal Halide, T5 Fluorescent and LED — Advanced Aquarist's Online Magazine

You can see from table2, the peak values are similar between the different lighting fixtures. However, this is only the maximum. Based on the graphs, the leds drop off quicker as they are more focused.

The author should really post the average and standard deviation instead of the peak, but the author does say:
"From this it should be quite clear that statements directly touting LEDs as being equal to 250W metal halides are correct as far a peak values of PAR are concerned. While the PAR values hit by 250W metal halides may be met, the area coverage must also be considered when making a valid comparison. The 250W setup as tested would be suitable for large tanks, roughly an area of 36"X30" would be covered by one such fixture. The T5 light setup has a more elongate distribution as expected from a 36" long light fixture, and covers an area roughly 36"X24". The Solaris I5 would provide light values greater than 100, over an area of roughly 20"X16", where as the KR-92 would cover an area of 24X18" at 30" above the aquarium. "


if we compare the coverage area of the KR-92 to the MH, 24x18 = 432 and 36*30=1080.

So, while the 110W KR-92 has a similar peak value to the 250W MH, it clearly is not 3 times more efficient. If the mean and standard deviation were published, over the entire area, they should be fairly similar.

Of course the Cannon wasn't tested and may very well be more efficient than the KR-92, but not by orders of magnitude...

 

HAHA Rob, I suppose proof of a product would put Half of the products out there on the market (not just aquarium supplies, but all products) out of business if we all could "try" it out before we decided to "buy" it.

It seems some of us who would happen to know anybody that works in these public aquariums who are converting to LED lighting, and ask them if they see any difference, perhaps MH lighting provides exactly, if not more than enough spectrum and coverage that most corals need for survival, and LED lights give them just the amount they need without any waste. You guys have provided me with so much material to look over I'll be busy for a week reading, But ultimately, the proof comes to the one who decides to bear the cost of converting their lighting system.
So, why doesn't somebody ask them?

 

By the way, I didn't have time to get to that supply store I was talking about, work got in the way, so I'll try again on Monday.

 

Really a rough question,400W led aquarium light is too hard to produce.

 

I just got a follow up email from ecoxotic. Clears things up a bit more but Id really like to see the actual measurements of par and spread at depth.
here is the message they sent.