LED colours/spacing questions

moorin said:

Ok thanks for that, I'm only wanting to use royal blues for the correct par/lumens (can't remember what you call it) for the plants need to photosynthesis. I've heard red isn't good for algae so if not I'd be quite happy with just cool white leds As long as it's beneficial for the plants.

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you have some things to learn/unlearn..
though admittedly some of it is "arguable"...

I know I would not personally build an LED fixture w/out 660nm reds.......
It is an obsession.. based on "best of my knowledge"... or AFAICT factor.

Currently my only questions are 1)Add UV to "shock" the plants into more color and shore up the deep blue response spectrum. and 2)reds other than 660...

Took me some time to add cyan. now I wouldn't build w/out it..

Next time..

moorin said:

So what's the general rule for colours as I haven't been able to find any info regarding the ratio between white leds and blues/reds etc. I don't want to over do it and get a horrible colour in the tank I want it as close to 6500k as possible so it looks pretty natural.

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Look at it this way.. say you ran 10 10000k whites on one channel
10 3000k whites on another
For the sake of simplicity assume they are looked at as equal in your eyes..

So when all are at "full" your CCT is 13000/2 =6500k

IF you shut the 3000k channel off you get a 10000k tank (at 1/2 luminosity of course)

now add colors for 2 reasons 1)add specific PAR regions and 2)broaden or flatten the spectrum

As you saw all "white" are not really white but a blue LED plus yellow phosphor giving an uneven spread..
WW and cool whites together help "flatten" the curves and in general are really all that is (in my mind and many opinions) necessary.. See how the warm white "fills in" a lot of the lower red area and has less blue.. Averaging those 2 curves will give you a flatter spectrum.. w/ one teeny exception, the 475ish region.. (this is where cyan LEDs come in but it is not perfect either. The "kicker" though is it punches up greens and you eye really likes green so it appears very "vivid", A WORD of caution.. some "cyan" leds are just a blue and yellow LED combined and DO NOT peak or fill the same way, though they "look" similar)
Throwing red (deep red 660nm) and royal blue (470nm) just add PAR "punch" so to speak..
Either running a seperate channel (recommended) or only modest use of them is recommended.
Interesting collection of "chatter" re this.
http://www.nano-reef.com/topic/310741-diy-full-spectrum-led-build/page-3

One not of caution: You must decide what "white" you like.. ignoring the 6500k aspect for now, and as I found out.. the warmer leds are more "visually warm" than the coll ones are "visually blue" if that makes any sense.

In other words if you like a crisp white look yet want a warmer fill (sunset dimming, just a bit of red pop) you wouldn't do 50/50 ww/cw but somewhere a bit lower.. say 2/1 ratio cw/ww. Again though, dimming is your friend.
BUT you also want to max. your output.
Gets tricky.. and to be honest,
I haven't even completely decided myself..I've had "just" 3500k and "just 6500K and now 50/50 3500k/6500k as "main lighting" and haven't decided which is a favorite.. The fill colors add "pop" to every fish color and plants are marvelously green but the overall tone, though FAR from bad.. well I'm just not sure.
Of course I broke my own recommendation by running a combined ww/cw channel instead of a seperate channel, thinking I was smarter than myself.....
Of course replacement LED's would be no problem..
More later

Think just to make things easier I am going to run 2:1 cw:ww as I am wanting sunrise/sunset dimming. I have been reading some of hoppys posts and I'm not too sure whether I want blues and reds now although they flatten out the spectrum the problem I've seen/read is you can end up with spots of blue and red.

The next issue is trying to work out par levels at the substrate which will be upto 36" distance from lights to substrate (tank is 28" tall minus 2" substrate plus hanging of the light) and I think 36 xml's will be overkill on a 50gal looking at other builds.

I am wanting to drive them at 2100ma so will be roughly 1000lm each but when I have a minute I'll use hoppys formula to work out the par as I have a funny feeling it's going to be well over the figure I want for a "high light" build.

Thanks again for your help/discussion

Except for the stevesLED's Cyans all are "generic" fleabay led's 3W
There are definite differences in individual LED's because of poor binning.. but overall nothing note-able
I'm driving the 3 channels at 700mA (all in series this time) No fans (hate fans) so I'm content w/ not pushing them. w/out fans the Al bars get to about 110F..43C well within acceptable range but def warm to the touch.
The cyans are noticeably more efficient when tested.. I use a D-VOM meter set to Ohms which has apparently enough voltage to light them.. albeit really really weak. Cyans "popped" pretty bright which was my judgement on their efficiency.. Some of the 3500k's were mixed dim or dimmer...RB and red tested fairly "consistent.. Not sure how valid the test is but can't think of a reason it isn't at least modestly effective.

I'm inherently cheap.. I think it is genetic..
The cyans I'm driving @ 1000mA but will eventually dim them down a bit..
I guesstimate to lose 10%-20% after 10,000hrs at this temp (heatsink temp +?(20) = die temp) ..that's about 4 years.. like I'll not rebuild by that time.. LOL


overall 31 x 3w LEDs MAX.. more like 60W total.... in reality..

DO NOTE that light in the image is not mine.. not sure that was clear..
Details here:
http://www.plantedtank.net/forums/showthread.php?t=613994