Widmer's LED Projection System

[widmer]

The beam projected from each LED is an 8° cone

This is not the case. (I was originally under this impression as well.)

The optics are named based on the FWHM standard. What that means is basically that, at an 8 degree cone width, you'll find that the light is half the maximum in the very center of the cone. That makes it sound like half the light is outside the cone, but it's typically less than that (intensity is usually dropping off VERY fast at that point), though it will vary based on the distribution of the particular lens.

Nice succinct explanation.

What I found from trying different lenses, is that the FWHM rating (ie 8 degrees in my case) can be very misleading. This is the reason I returned a bunch of 6 degree optics; those particular optics actually appeared to cast a wider beam than the 8 degree optics I am currently using. This is because the degradation of the beam outside of the FWHM point is not equal for different lenses. And on top of that, the data sheets will show you a chart that gives you the general idea but IMO is very imprecise of the true appearance of the rate of intensity degradation outside of the maximum point.

What's worse, is these 6-degree lenses absolutely did not display on their FWHM chart that they cast a terribly ugly sharp intense rim at the very edge of the beam. That was an instant dealbreaker.

While we're on the topic, I absolutely love my carlco medium ripple 16 FWHM lenses from LEDSupply. They cast a fantastically even beam in case anyone's looking for optics of approximately that width beam.

 

[BeanAnimal]

Did you happen to take a reading at say, 1 foot or 2 feet from the fixture? It is my understanding that light obeys the inverse square root law. So if you are getting 300 par at 4 feet, would that mean that you are getting 90,000 par at 2 feet? That just doesn't sound right. But it would be interesting to know how much you lose due to the height of your fixture. Thanks again,
Joe

Without getting into a lot more detail, the inverse square law applies to a point source. Light that travels through an optic does not follow that law.

 

[der_wille_zur_macht]

It is my understanding that light obeys the inverse square root law.

That's more or less true for a plain old point source projecting in all directions, but optics basically throw that out the window, at least as far as an application like this is concerned - The constants in the function that determines intensity go through the roof.

Imagine two scenarios:

1) A sphere

2) A flat, 2d square

In both cases, imagine the light is projected perpendicular to the surface of the two objects. The light from the sphere will be cast in every direction so it will disperse quickly. The light from the square will project linearly and won't spread at all, so in a vacuum, it'll be the same intensity at 1 foot as at a million feet.

An LED with a tight optic isn't a perfectly linear light source, but it's closer to the square than the sphere.

 

[BeanAnimal]

This is not the case. (I was originally under this impression as well.)

I guess it was a generalization, where an explanation such as those both of you provided would have been more informative

 

[der_wille_zur_macht]

While we're on the topic, I absolutely love my carlco medium ripple 16 FWHM lenses from LEDSupply. They cast a fantastically even beam in case anyone's looking for optics of approximately that width beam.

Same thing for their Luxeon Rebel lenses, I love them. Too bad they're not available in a wider range of sizes.

 

[widmer]

Did you happen to take a reading at say, 1 foot or 2 feet from the fixture? It is my understanding that light obeys the inverse square root law. So if you are getting 300 par at 4 feet, would that mean that you are getting 90,000 par at 2 feet? That just doesn't sound right. But it would be interesting to know how much you lose due to the height of your fixture. Thanks again,
Joe

Your understanding is correct, but doesn't quite apply here. The inverse square root idea is for a light radiating from a single point in 360 degrees with no overlapping beams. Using the lenses, this light is focused into a beam and not allowed to travel outside of a given area. Just like any spot light, it is not allowed to spill out.

Skippyreef feel free to chime in here (he brought over the PAR meter) but if I remember correctly, when I held the sensor a few inches out from one of the LEDs, it read something like 2,000 unfortunately not 90,000

 

[widmer]

I guess it was a generalization, where an explanation such as those both of you provided would have been more informative

A correct one-sentence generalization would have been to multiply the degree rating by somewhere between 1.5 and 2, and say something like:

"It means that it will cast a 12-16 degree cone of light, with the middle part being the brightest."

 

[BeanAnimal]

A correct one-sentence generalization would have been to multiply the degree rating by somewhere between 1.5 and 2, and say something like:

"It means that it will cast a 12-16 degree cone of light, with the middle part being the brightest."

Or the bulk of the light is meant to be cast in a 8 degree cone... thus the 8 degree nomenclature.

 

[salty joe]

Thanks all for the informative replies.

 

[ReefEnabler]

love the led fixture perfect example of a design that leverages the strengths of leds/optics to the benefit of efficiency and aesthetics.

Curious to hear if anybody else has tips for soldering those really difficult star pads from a certain vendor..

You simply have missed the entire point and context of the post, light and its behavior are the known quantity. Honestly, this is getting kind of silly.

your point about a theoretical projected halide 'blowing away' LEDs has been obvious to most. Usually you are so helpful, but all I see here is preaching to the choir. If you want to help with with these concepts, it would be more productive to develop such a Halide lighting system and share your findings. In certain applications, Leds let you focus the light more efficiently for comparatively less effort. Given enough effort/ money, the same could be done to any light source. Everyone gets it. A reminder of this need not be in every thread, just because one poster showed a slight misunderstanding. Leds are not magic. Lesson learned. Achievement unlocked. But they can be darn effective if propey sized and projected.

 

[BeanAnimal]

your point about a theoretical projected halide 'blowing away' LEDs has been obvious to most. Usually you are so helpful, but all I see here is preaching to the choir.

You too missed the point. Nobody was preaching anything. My comments were not negative towards the LEDs or positive towards MH lighting, nor were they argumentative.

If you want to help with with these concepts, it would be more productive to develop such a Halide lighting system and share your findings.p

I have absolutly no desire or use to design or build such a system, nor would it prove anything that isn't already known science. Suggesting such an undertaking is kind of silly.

Everyone gets it...

No, everybody does not get it. That very concept is what drives the content and discussions in these forums. If everybody "got it" then nobody would ask questions and nobody would need to answer questions. I don't know about you, but I learn something new every day and am thrilled when people go out of their way to explain a concept or technology that I am not well versed in.

It amazes me how hard some of you are trying to have an argument about a subject that I have clearly not attempted (nor have a desire) to argue about.

 

[widmer]

You too missed the point.

There seem to be lots of folks missing the point here so let's revisit the comment I perceive there to be disagreement about:

I would imagine your painting with a broad brush just to illustrate how well the project turned out, but I hate for people who are just learning to walk away with the wrong idea.

If we took a 150W halide with a reflector that focused on the same footprint as the LEDs, then it would blow the LEDS away even if the MH in question was only 75 lW and the reflector was only 70% efficient vs the LEDs with 100 lW output and 100% efficient optics. A 400W halide in the improper reflector would still very easily produce more than 300 par in the main focus area at a distance of 4-5'

Is this so? Let's try the math in a few scenarios:

For the halide:
150w * 75 lumens/w * ~70% efficient reflector housing = ~7,875 lumens

For the equivelent watts in LED:
150w LED * 100 lumens/w * ~100% efficient lens = ~15,000 lumens

So for the same wattage, the LED system is producing almost exactly twice as much light. So the LEDs aren't necessarily being "blown away". Or were you referring to a 150w halide blowing away the 72 watt LED fixture I built?

Using the same situation design, we would simply divide the value for the LED in half (I'm using half the wattage), and we come up with ~7,500 lumens. I still don't see the LED fixture being blown away.


Now let's make more fair/realistic conditions:

We will use the same MH values you dictated for the halide (I'll have to take your word for this, I know nothing about the halides) but we will use numbers that are true to life for LED systems:

halide:
150w * 75 lumens/w * ~70% efficient reflector housing = ~7,875 lumens

LEDs:
150w * 120 lumens/w * ~85% efficient lens = ~15,300 lumens

Again, it is unfortunately the halide which is being blown out of the water.

Note: This is assuming that we are at the point in time of 75 lumens/w for the lumen maintenance of the halide. Halides lose an enormous percent of their output as they age, thus the reason folks replace them so long before they truly burn out. Also, we have moved to 120 lumens/w because this is approximately the efficiency of the XP-G LEDs everyone is using now. I believe I may be one of the last XR-E users around Also, I used 85% for the efficiency value, because this was the very lowest efficiency estimate I came across while looking over LED lens data sheets. Most were above 90%.

And finally, let's visit the part about the 400w MH. You stated "A 400W halide in the improper reflector would still very easily produce more than 300 par in the main focus area at a distance of 4-5' ". I suppose I would have to see evidence of this to believe it. Sure light is predictable, but I've had a number of people including DWZM and Skippyreef tell me that in their experience, in real life, they have seen such PAR values from 400w halides at said distance.

How does all of this sound to folks?

 

[BeanAnimal]

Or were you referring to a 150w halide blowing away the 72 watt LED fixture I built?

The comments were clearly in context to the 75W of XR-E LED you are using in your system, as that is what DZW's comments were in context to.

The 75 lW value was chosen as a low end realistic MH output value. Real world values range from 70-110 lumens per watt, depending on the spectral output and type of MH lamp.

The 70% efficient reflector value was also chosen as a reasonable low end for a decently shaped reflector.

In the same nature, the LED's lenses are not 100% efficient. The 75W of the XR-E LEDs in question are not all producing 100 lW and are not putting it ALL into the focus area. I chose 100 lW becuase you did not indicate what BIN you used. I also assumed that they were all WHITE and in fact you have 1/2 Royal Blue.

Again, I don't care about the XR-G or any other LEDs. My comments were simply with regard to what was stated. Of course XR-Gs will fare better in a head-to-head than XR-Es.

So using the MH numbers from above and applying your "real world" numbers to the XR-E

150W of MH at 75 lW = 11,250 Lumens.
11,250 Lumens at 70% reflection = 7,875 Lumens in the tank.

75W of LED at 100lW = 7,500 Lumens
7,500 Lumens at 85% efficient lens = 6,375 Lumens in the tank. If ALL 75W were cool white.

I am amazed that something so simple has been obsfucated to the extent that it has been. The comments HAD ABSOLUTELY NOTHING to do with what lamp was better, more efficient or more appropriate for reef lighting. They were not a dig against LEDs or your project or an attempt to infer that MH was better. The comments were simply in context to the innocent statement by DZW.

Lastly:
Take the 400W halide at 4'
400W of LED at 75lW = 30,000 lumens
Nearly 80% of the light would have to miss the tank for the fixture to be worse than the 75W of XR-E.

 

[widmer]

In the same nature, the LED's lenses are not 100% efficient. The 75W of the XR-E LEDs in question are not all producing 100 lW and are not putting it ALL into the focus area.

You may want to double-check my post, my latter calculations are made assuming the lenses used with the LEDs were the absolute lowest efficiency published, 85%. I was simply plugging numbers into the situation you outlined.

I am now intrigued by the 70% efficient reflector you are describing in the case of the metal halide system as being reasonable. What exactly is this efficiency describing? Again I know nothing about halides, so I am curious. Is it describing simply its ability to push light outward away from the fixture? This is my guess. I don't beleive you could find halide reflector efficiency data which makes a fair comparison to the LED lens efficiency data.

If 70% is considered reasonable for this purpose of simply pushing the halide light in a general direction over a short distance, I would be very surprised if you could in fact reasonably design a halide reflector that could project light into a 2 square foot area at 4 foot distance and still acheive this efficiency, again due to the fact that the emitting area of a halide is nowhere near as compact as an LED, for it being considered a "point source" light.

Your 70% efficiency may in fact be overly generous toward the halide, and your 110 lumens per watt are guaranteed not to last more than a couple of months due to the characteristic lumen maintenance of halides.

Correct me if I'm wrong on the point of the lumen maintenance.

 

[widmer]

So using the MH numbers from above and applying your "real world" numbers to the XR-E

150W of MH at 75 lW = 11,250 Lumens.
11,250 Lumens at 70% reflection = 7,875 Lumens in the tank.

75W of LED at 100lW = 7,500 Lumens
7,500 Lumens at 85% efficient lens = 6,375 Lumens in the tank. If ALL 75W were cool white.

In the name of not misleading folks, in this case after you have made the calculations, do you still stand by your original statement and find the halide which is consuming twice as much electricity and putting only ~20% more light into the tank to be blowing the LED system out of the water?

Again, this must remain hypothetical, because we don't presently have any data which tells us that a halide reflector could even attain 70% efficiency at this distance to begin with.

 

[g8gxp]

Ok now I'm totally confused. When i started my own led venture I tried to calculate
my needs based on lumens but was told that it was essentially a useless metric and that what I should be concerned with is PAR. now I see lumen comparisons. Which measuring stick should we be going
with?

Second, when comparing light efficiency is a 75% efficient halide reflector putting the same PAR in the same footprint of the tank as a 75% efficient LED fixture such as the one under discussion, with mounting height being equal? Or are there just too many variables to make an adequate comparison?

My head is swimming...

 

[BeanAnimal]

You may want to double-check my post, my latter calculations are made assuming the lenses used with the LEDs were the absolute lowest efficiency published, 85%. I was simply plugging numbers into the situation you outlined.

No Sir, you were not. I did read your post. You plugged those numbers into a MORE EFFICIENT generation of LED. I was talking about the 75W of LED in your project, not some other project.

This is why pointless arguments start. With each post, we get further from a simple point.

I did not not use 110 Lumens per Watt for a halide, I used 75 Lumens per Watt. I posted the range in which the technology is capable of yielding becuase you said you knew nothing about Halides.

If you wish to read about reflector efficiency, then the articles by Dr. Sanjay Joshi are a good starting point.

 

[BeanAnimal]

In the name of not misleading folks, in this case after you have made the calculations, do you still stand by your original statement and find the halide which is consuming twice as much electricity and putting only ~20% more light into the tank to be blowing the LED system out of the water?

I will very kindly remind you that my remarks were very clearly in context to those made by DZW. No more, no less.

How you choose to define "blown away" is certainly up to you. My meaning was clearly with regard to total lumens placed in the measurement area as inferred by DZW, not with how efficiently they were placed. The 400W MH bulb was used as a reference by DZW and I chose to use a 150W for juxtaposition.

 

[widmer]

This is why pointless arguments start. With each post, we get further from a simple point.

I'm content; This discussion was very productive in illustrating how blatantly more intense and efficient LEDs are as a source of light, as compared to a halide.

We couldn't have done it without you

 

[BeanAnimal]

Ok now I'm totally confused. When i started my own led venture I tried to calculate
my needs based on lumens but was told that it was essentially a useless metric and that what I should be concerned with is PAR. now I see lumen comparisons. Which measuring stick should we be going
with?

PAR data is not something that is measured or published by lighting manufacturers. Lumenous data is published. While PAR and Lumens do not measure the same thing, they are close enough to give us a rough idea of how a light will perform.

Second, when comparing light efficiency is a 75% efficient halide reflector putting the same PAR in the same footprint of the tank as a 75% efficient LED fixture such as the one under discussion, with mounting height being equal? Or are there just too many variables to make an adequate comparison?

Way too many variables. Most of the MH reflectors sold to our hobby are pretty bad. There are a select few that are very efficient.

Widmer, DZW and others here who have built LED projects can be of great help with regard to how many you need and what lenses to purhcase. If you want to learn about MH lighting and how it is measured, then google Dr. Sanjay Joshi.