Anyone Thinking of Dumping LEDS and going back to Halides

[zachts]

Keep in mind though that that MH reflector lets say is 12" square and emits a fairly uniform light reflected in all directions beneath that 12" square point source. Now an equivalent LED multichip is emitting all of its light from an area of 1.5" square or so, and that may be focused even more into a very tight beam with optics. It is a huge difference in the way the light beams behave within the tank.

 

[scolley]

Yes, but you've just reworded the same thing Zachts... "uniformity" is the same thing as rtparty's comment that it "spreads the light out". And that's missing the point. So maybe I need to be more clear.

mhucasey stated "panel type lights with many LEDs help to bathe the coral with light from more angles". If I may paraphrase that, non multi-chip leds (lots of spread out separate LEDs) hit the corals from many different angles, if not too restricted by optics. That's NOT about the uniformity of the light that's emitted. That's about the large number of angles (or wide range of angles) that the light hits the corals.

I'm inclined to think there might be something to that, given my personal observations of other people's LEDs and success - or lack thereof - along with my own experiences.

However, the fact is that while a well reflected HM may spread light out that's very UNIFORM over a large area, the angles at which light hits each coral is not that broad a range. Uniform - Yes. Many different angles - No, pretty narrow range of angles. As stated before, the range of those angles is restricted to the widest portion of the reflector.

While the idea that the light hitting from a broad range of angles is important, the fact is that HH do not. So while it might help non multi-chip LED, it appears to not be critical.

Apologies if this seems argumentative. That's not my intent. I'm looking for clarity, and I believe we are talking about two very different things.

 

[heritage]

One other thing to take into account when trying to compare leds to mh and t5 is reflection.
Mh and t5 flood the area with light and a lot of that light is reflected off of the sides of the tank hitting the coral from all sides. Leds are much more focused which is why the led lit tanks look much darker.

I remember a tank I had set up a few years ago that was bare bottom and all live rock sitting on a rock lift. Lit by t5's I had coraline algae covering the underside of the rock before it even started to grow anywhere else.

 

[Aqualund]

I think you may be downplaying just how much a variety of angles can be provided from a MH bulb and reflector. Yes, the reflector has its specific facets...but the light emitting from the MH bulb is a spherical wave...meaning it is unpolarized light traveling in every direction and every angle before it hits the reflectors...and the the reflectors guide it to it the tank.

The allows for an infinite number of angles for the light to travel relative to the surface of the water.

Im not saying this as an advocate for MH or anything, I'm just saying in general...there is something to be said for the near infinite number of angles provided from a spherical point source of light. This will by definition have many orders of magnitude greater possibilities for direction than a half-sphere point source, that is already smaller in "volume" (led point vs MH point is smaller...making its irradience drop off curve shorter in distance).

So, like you said, the solution may just require a crap load of leds...but I think we may be able to solve this by more efficient means as well.

 

[scolley]

OK, I'm going to take a final stab at this, then I'm done.

One other thing to take into account when trying to compare leds to mh and t5 is reflection.

Good point. May be a factor, but how much light is actually reflected back to the corals? Does anyone know?

I think you may be downplaying just how much a variety of angles can be provided from a MH bulb and reflector.

Not at all. As you said. It's infinite. However that argument does not hold up because an LED with optics, because while the optic is narrow, it does have width. So the angles of light coming from there are infinite too in number too. Ergo the number of angles is not the issue.

What the original point was about is not the NUMBER of angles - both are infinite. It's about the RANGE of angles. For example...

In a 30" wide tank with one MH reflector, hanging with the bulb 20" above the average coral, if the reflector is rectangular, and 10" across at it's widest (measured corner to opposite corner), there will be in infinite number of angles of light. But the range of the angles at which the light strikes that coral 20" below it will be no more than 28 degrees in range. Roughly. From the coral's perspective that's 0 degrees from the light coming from directly above it, 14 degrees to the right from light coming from one corner of the reflector, and -14 degrees from the left opposite corner. And obviously light from all the points in-between.

But what if we take an LED fixture the same height over the same coral, but the fixture is 30" wide, or 30" between the center of the left and rightmost LEDs? In that case a coral 20" down in the center of that fixture is getting light from a 72 degree range. Roughly. 0 degrees straight up, 36 from the right, -36 from the left.

So the question is not about the NUMBER of angles. It's about the RANGE of the angles that the light can hit the coral from.

What we can say about those two scenarios is that while the HM light is a narrower range, it's far more uniformly spread within that range.
OK. I'm done with this point. :deadhorse: Thanks.

 

[meshwheel]

I have to say I too will more then likely never go back to halides. My led's give me better spread and coverage then any metal halide could ever do.
I have the reefbreeders photon 32 and so far I love it! No color lose whatsoever! It's a amazing light at a excellent price.
I was going to go 2 250 watt halides. Now, I am burning about 120 watts! Ha! Love it!
No heat. My chiller has not kicked on one time yet since the new tank has been set up with led's...........

 

[chilwil84]

OK, I'm going to take a final stab at this, then I'm done.


What the original point was about is not the NUMBER of angles - both are infinite. It's about the RANGE of angles. For example...

In a 30" wide tank with one MH reflector, hanging with the bulb 20" above the average coral, if the reflector is rectangular, and 10" across at it's widest (measured corner to opposite corner), there will be in infinite number of angles of light. But the range of the angles at which the light strikes that coral 20" below it will be no more than 28 degrees in range. Roughly. From the coral's perspective that's 0 degrees from the light coming from directly above it, 14 degrees to the right from light coming from one corner of the reflector, and -14 degrees from the left opposite corner. And obviously light from all the points in-between.

But what if we take an LED fixture the same height over the same coral, but the fixture is 30" wide, or 30" between the center of the left and rightmost LEDs? In that case a coral 20" down in the center of that fixture is getting light from a 72 degree range. Roughly. 0 degrees straight up, 36 from the right, -36 from the left.

So the question is not about the NUMBER of angles. It's about the RANGE of the angles that the light can hit the coral from.

What we can say about those two scenarios is that while the HM light is a narrower range, it's far more uniformly spread within that range.
OK. I'm done with this point. :deadhorse: Thanks.

i dont run mh or leds (currently)but most of the good mh reflectors are 16 X 16 square so they create a wider coverage than 10" diagonal while many led figtures are only 12 X6 so they need wide optics and height to match the coverage of mh.

most people that dont like mh coverage usually have experience with fixtures that have the small double ended mh bulb built into a combo t5 not the large pendents that also have the highest par

 

[rich850]

OK, I'm going to take a final stab at this, then I'm done.

Good point. May be a factor, but how much light is actually reflected back to the corals? Does anyone know?

Not at all. As you said. It's infinite. However that argument does not hold up because an LED with optics, because while the optic is narrow, it does have width. So the angles of light coming from there are infinite too in number too. Ergo the number of angles is not the issue.

What the original point was about is not the NUMBER of angles - both are infinite. It's about the RANGE of angles. For example...

In a 30" wide tank with one MH reflector, hanging with the bulb 20" above the average coral, if the reflector is rectangular, and 10" across at it's widest (measured corner to opposite corner), there will be in infinite number of angles of light. But the range of the angles at which the light strikes that coral 20" below it will be no more than 28 degrees in range. Roughly. From the coral's perspective that's 0 degrees from the light coming from directly above it, 14 degrees to the right from light coming from one corner of the reflector, and -14 degrees from the left opposite corner. And obviously light from all the points in-between.

But what if we take an LED fixture the same height over the same coral, but the fixture is 30" wide, or 30" between the center of the left and rightmost LEDs? In that case a coral 20" down in the center of that fixture is getting light from a 72 degree range. Roughly. 0 degrees straight up, 36 from the right, -36 from the left.

So the question is not about the NUMBER of angles. It's about the RANGE of the angles that the light can hit the coral from.

What we can say about those two scenarios is that while the HM light is a narrower range, it's far more uniformly spread within that range.
OK. I'm done with this point. :deadhorse: Thanks.

Just measure par at angles through your tank measure distances between and get back to us on this one maybe hang your best led the size of a lumen arc next to a smaller reflector like a cayman sun and measure par and you will see there will still be greater differences a couple inches away under the LEDs unless they are almost overlapping so what was your point exactly????

 

[scolley]

No need to waste space on this thread asking me Q's about my point. As stated before, I'm through discussing this. Either my point was stated by me in a way that could be understood, or it was not. I did my best.

I'll be happy to chime in on other subjects. But I'll waste no additional time on this one. Let's keep this productive. IMO it's an important thread.

 

[Aqualund]

Good point. May be a factor, but how much light is actually reflected back to the corals? Does anyone know?

with highly reflective aluminum, nearly 98-99% of incident light will be reflected...that is why they use this metal and not any other...it has the best coefficient for reflection without absorption.

So the angles of light coming from there are infinite too in number too

No, you are wrong. You take the wave equation http://www2.ph.ed.ac.uk/~paboyle/Teaching/PhysicalMaths/Notes_2010/notes_2010_part3.pdf and divide it by 2 because it's only half a sphere...this results in orders of magnitude less propagation angles in 3 dimensional space than a full sphere like a MH bulb light source.

No need to waste space on this thread asking me Q's about my point. As stated before, I'm through discussing this. Either my point was stated by me in a way that could be understood, or it was not. I did my best.

I'll be happy to chime in on other subjects. But I'll waste no additional time on this one. Let's keep this productive. IMO it's an important thread.

The frustrating point about this is that your interpretation of this is wrong...and I am a physics major who just finished an entire semester of electro-magnetism and optics.

I appreciate the point you are trying to make and it goes a certain distance in proving that whatever shortcomings might be inferred from not using reflectors like MH's...isn't that big of a deal when you use lots of leds...

The key thing you are forgetting is the multiple reflected rays of light that hit the reflectors numerous times before entering the water...so even with your reflector but especially with the round shaped reflectors, the incident angles far exceed 28 degrees like you say.

But fundamentally, there is a difference in the range of angles the light can travel...those ranges are less with leds than MH's with reflectors...and must be compensated for...with more leds.

It's possible I may not be able to explain it much differently without getting into maxwell's laws of electro-magnetism and/or doing a spherical wave integration to prove the difference ...but I might just do it to help the discussion.


You can't just say "I'm right and your wrong and I don't want to talk about it anymore." Removed~dc

 

[dom418]

While LED technology has improved significantly within the saltwater hobby, I went back to halides and couldn't be happier. I can't justify spending that kind of money on LED fixtures to have a newer/better generation hit the market 6 months later. For example Radion G3. It's like Apple for crying out loud! Just when you think you have the latest, a new model comes out.

I'll wait until these manufactures get it right for good before I switch. Custom setups like from ledgroupbuy sound like a better option than fixtures though.

 

[power boat jim]

While LED technology has improved significantly within the saltwater hobby, I went back to halides and couldn't be happier. I can't justify spending that kind of money on LED fixtures to have a newer/better generation hit the market 6 months later. For example Radion G3. It's like Apple for crying out loud! Just when you think you have the latest, a new model comes out.

I'll wait until these manufactures get it right for good before I switch. Custom setups like from clay-boa sound like a better option than fixtures though.

I dont know why people think they have to keep upgrading their LED systems every time a new one comes out. Im using the same ones I bought over 2 years ago and they are more then adequate. If you buy a good unit to begin with you wont need to upgrade it. There is no need for "cell phone mentality" when using LEDs

 

[TropTrea]

I think the big issue here in this reflector and light spread discussion is two people talking about it in different terms which is making them confused as to what the other individual is saying.

What Scolly is basically saying is that if have a MH reflector that is 10 inches square and your lighting a point that is 10 inches away the light light will be hitting that point from points no more than 60 degrees from each other.

What Aqualund is saying is that the light from the reflector will be generated out in many different angles not restricted to the 60 degree angle.

Your both true on this however your difference is one is looking at it from the light source and the other is looking at it from the point where the light hits.

Perhaps we should look at it from a completely different prospective. Lets take a Ball with 4" Diameter and suspend it from the center of a light source that is 10" away. Now ask yourself and sketch it out on paper with two completely different light sources. One light source would be a 10: X 10" square generating beams of light in all directions from its source. The other light source would be a grid that is 20" X 16" square with a an individual LED spaced every 4 inches with 120 degree lenses on them. Now if there no other light in the area which would light up the most surface area of the ball.

Now we can move a reflective shield with a radiius of 12" and height of 20" around this ball. How will this change the way the surface of the ball is lighted up?i n both cases. This would be an example of adding the reflection off the glass sides of the aquarium if there reflective ability was 100%. In reality the amount of light reflected off the glass is considerably under 100% and dependent on many factors can be extremely less.

Now lets do these experiments over again and use a milti chip LED with a 120 degree lens. But this multi-chip LED only measures 1 square inch in size. How has this changed the results of your experiment?

 

[Aqualund]

this is what im saying :

Please remember, I am an LED advocate. All I use is leds over all of my systems...so this is coming from the point of identifying some of the shortcomings and showing ways to overcome them.

 

[Nano sapiens]

Yes this is why I moved away from the higher output multi-chip LED's and moved back to the lower to medium powered individual LED's. You also have here as issue of appearance where spotlight lights the top corals and produces big shadows on anything onder it. It produces a very high contrast look.

This is basically the direction I've gone with my LED array, just on a much smaller scale. I think that we'll see more of this type of array in the years to come and less people having trouble using LED lighting.

 

[mhucasey]

this is what im saying :

Please remember, I am an LED advocate. All I use is leds over all of my systems...so this is coming from the point of identifying some of the shortcomings and showing ways to overcome them.

You beat me to it!. I got caught up drawing lots of arrows

 

[dc]

Ok kids let's tone it down some. I swear people will argue over anything.

 

[Brian Crook]

I think that's why there's more than 1 LED in these fixtures.

 

[meshwheel]

LOL, and probably NONE OF THEM OWN A PAR METER. This is where newbies come in and leave more confused then when they got here!
Powerboat Jim: I could not agree more! I will have my lights for quite some time(God willing) and I could not be happier with them. I am really going to save save save!!!!
I have no hot spot at all with the ReefBreeders fixture, as the led's are spread out the entire length of my tank. I love the 90 degree optics too.
I have ran metal halides for close to 20 years. I DO NOT MISS THEIR HOTSPOTS ONE SINGLE BIT!

 

[Fredfish]

I dont know why people think they have to keep upgrading their LED systems every time a new one comes out. Im using the same ones I bought over 2 years ago and they are more then adequate. If you buy a good unit to begin with you wont need to upgrade it. There is no need for "cell phone mentality" when using LEDs

The same reason they need to upgrade their phones every two years, their cars every 4 years... We liven in an advertising driven society of over consumption.