Modern LED scrubber light

Does anyone have an opinion about the importance of CRI for growing algae?


The color rendering index (CRI) (sometimes called color rendition index), is a quantitative measure of the ability of a light source to reproduce the colors of various objects faithfully in comparison with an ideal or natural light source. Thanks wikipedia


From what I have been reading I notice that some bulbs that are classified as full spectrum are done so because they have a high CRI i.e. greater than 80 and also a color temp higher than 5000K

Although I have a seen grow bulbs with only CRI values greater than 60. I guess with a grow bulb you are less likely to be concerned with how the colors of the plant appear and might have different mix of kinds of phosphor to achieve the different wave lengths that would be beneficial.

It seems that there is no real standard for terms like full spectrum and grow bulbs and they may not be interchangeable.

Why I ask is there seems to be a trend for led makers to produce leds with higher CRI values.

Namely I am looking at The LXML-PW71 Luxeon® Rebel White - ANSI 3000K which has a 90 CRI and a very narrow 2870K-3220K color temp

Sharp also has a new line of 6.7 watt Zenigata LEDs that have a high CRI (87) which only started to be manufactured last month.

Thanks for any help

You do not really want full spectrum for growing algae.
Well, specifically, it is a waste of power. It does not actually hurt.
Chlorophyll (Algae) are green, because they do not use the green part of the spectrum.
Or for that matter, a whole lot of the center.
Look at en.wikipedia.org/wiki/File:Chlorofilab.png for a nice drawing of the spectrum that plants like.
You really want something high in blue/purple and red/orange.

In a perfect world, you could pick exactly what you need.
An easy alternative, is "warm white" with a bit of extra red.
The nice thing about "warm white" LEDs, is that they are fairly close to what you need, but wide spectrum enough that
you don't have to be very exact..
I added some red for the upper end. I have some red/orange on order, to see what that looks like as well.
The fundamental color of those white LEDs is really blue. They use phosphors, activated by the blue, to produce the other colors.
Look at LED datasheets for spectrums produced.

By the way, do not equate narrow color temp with narrow spectrum.
Narrow color temp simply means that it does not change much from batch to batch, component to component, and current to current.
Really more of a measurement of quality.

For that matter, color temp does always tell you much about true spectrum anyway.
It is simply the average of the spectrum. What YOU perceive. Well, sort-of. Simple way to think about it.
Since algae ignore so much of the spectrum, it can be very different from what they perceive.
And LEDs have such a strange spectrum, the average can even be in a wavelength that they barely produce.

Thanks for the reply

Why I ask is I am getting growth on my horizontal algae scrubber but not too much, granted it has only been going for less than a week. I am impatient

because I

bought 6 discus 5 of which are really sick from LFS. They weren't having to much success so I picked up all of them for $100. A steal if they live.

I added 4 normal 2700K 13 watt cf two days ago and 5 rebel cool white + 1 red rebel too the scrubber today. I have a feeling that since the colored leds have a

narrow frequency that it would be easier to dial in white leds if you have the right kind. Possibly ones with a high CRI. There seems to be new kinds of leds

coming out every month. Understandably you will be wasting some frequencies of light but with all the other benefits of leds I will look past that to get results.

Has anyone have an opinion on all the 10,20,30,50, and 100 watt leds that are all over ebay? 100 watt warm white led with a diffuser might work well.

It could be put together for $!50 and that is 6000 lm. I am going 1o add a 10 watt warm white and a 10 watt red once they arrive.

Quote:

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Originally Posted by inkidu

.... I have a feeling that since the colored leds have a narrow frequency that it would be easier to dial in white leds if you have the right kind. ..... Understandably you will be wasting some frequencies of light but with all the other benefits of leds I will look past that to get results. ....

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Yes, this was similar to my thinking as well. Get something spread out, then fill whatever spectrum holes are left.
I have 3 warm white, and 2 red.
But looking at the waveform, I am wondering if I need more blue.
There is a real gap between 450 nm and 500 nm.
The blue part of the while LEDs seems to be more in the violet range, and very tight.

KEY PROBLEM with the big high wattage LEDs is the heat sink!
At 2W, a simple aluminum angle bracket is fine.
At 50W+, you are talking a CPU quality heat sink, with fan.

Another issue SM already pointed out is diffusion of the light. Fixable with diffusers, but that absorbs light.

I might very well experiment with more pure LEDs though.
I am thinking purple + blue + red-orange + red, all in equal numbers. Probably 3 of each.

GENERAL UPDATE:
My ATS is still not growing well at all. Minimal slow growth.
That really says little about LED/CFL btw. My old CFL was worse. But could have been placed wrong.

That said, I am fairly happy with so far anyway.
The hair algae in the main tank is actually looking a bit less healthy.
It was not really growing before, but not dying either. Now it is going a bit grey where light is less intense.
My nitrates remain at zero, so nothing expected there anyway.
My corals seem a bit happier. Especially my pipe-organ. This is probably due to the increase in pods, or
maybe a subtle increase in water quality.

NEXT STEP:
I first have to modify my sump. Various reasons. But part of that will be to lower it, allowing more room for ATS.
Then, I plan to make an improved two sided ATS.
At that point, I will use standard CFL on one side, and LED on the other.
Real scientific like.
Also, it will then be large enough that I can more safely experiment with turning off my protein skimmer.

I really think the answer is an array of low power LED's; one every 1/2 inch or so. Then of course there is the light-screen version:

viewtopic.php?f=3&t=34

That really only solves the diffusion issue.
And I did measure it, and I just don't see how that could really be a problem.
But even if it is, it can be solved pretty easily with a simple diffusion screen.

You need to be really careful with efficiency.
- I assume when you say "low power LEDs", you mean the modern "bright" 5mm ones. Those can be good or bad.
- But the old tiny ones are terrible as far as cost/lum and watts/lum. Don't even go there.
- Power supply becomes an issue as well. You either need really high voltage for the long chain, or several small supplies.
- Small supplies are usually not PWM/DC-DC, so far less efficient.

The big problem of course, is that it is a royal pain to build.
- That is a lot of soldering to do.

But yes, ignoring effort, with a proper design, and especially with a real PCB, it might be the best.

I got 4 of these heat sinks for $64 shipped off of ebay.

Aluminum Heat Sink 10"x7"x3"

I connected six rebels and have not notice the heat sink even get warm

Probably over kill but I wanted to run fan less

Do you think a heat sink that size could handle a 100 watt led?

I have some experience wiring 120 mm computer fans to run at 5 volts making them nearly silent.

I have a local glass store in town that showed me a completely clear glass with a wavy surface.

Might still produce hot spots but maybe less of them. At least it would not block transmission so much.

Anyone try something like that? Do you think it might be an good diffuser?

I trying to get large wattages because it seems cheaper and easier to setup than so many small ones.

What does anyone think of a 100 watt warm with some distance between the screen and a diffuser?

Thanks for any help

Well.. You can clearly over-watt algae. I don't know at what level though.

That size heat sink would be enough for 100W especially if you have a fan moving the air correctly past the fins.

You should probably keep the light back far enough to have relatively uniform light across the screen.

More sane would probably be a handful of 1W LEDs spread around heatsink. That way you get more uniform coverage without the concentrated heat.