how many LED's?

Discussion in 'General Electronics Chat' started by Bear_2759, Aug 18, 2010.

  1. Bear_2759

    Thread Starter Active Member

    May 23, 2008
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    Hi guys, how would you suggest I calculate number/type/specs of LED's to replace a fluro?

    personally I'd prefer to work with thru hole over SMD's.

    it's for a small project I'm working on is to replace a fluro in my fish tank.
     
  2. Wendy

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    Mar 24, 2008
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    I don't know if it would work, but does a fluorescent come with a lumens rating? LEDs do.
     
  3. t06afre

    AAC Fanatic!

    May 11, 2009
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    I am not an expert on this. But is not a a fluro important for the plant growning in your fish tank. I do not think LEDs emit the type of light that plants need
     
  4. mcgyvr

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    Oct 15, 2009
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    Not true. Many plant growers and saltwater reef tank owners are switching to LED's (mostly for the decreased heat output). LED's can be purchased in many different color spectrums that are excellent for plant growth (or coral growth in saltwater reef tanks). In fact many are seeing that LED's increase plant growth over other setups like metal halide and high pressure sodium bulbs as the light can be setup to give the exact color spectrum needed for optimal growth.
     
  5. t06afre

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    But you can not take "any" LED, you have check the spectrum (from data sheet) first? It has been a while since I looked at LEDs that deep
     
  6. SgtWookie

    Expert

    Jul 17, 2007
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    You really would not want to work with thru-hole LEDs for a project like this. You would need far too many in order to produce the amount of light needed, and then you would have problems with heat dissipation.

    My eldest stepson has a salt water fish tank, and has an assortment of high-intensity lamps providing a great deal of illumination, and supporting fans to provide cooling. I don't recall what all he has connected, but he has a 15A 120v outlet maxed out, so about 1,800 Watts.

    Cree makes some very powerful LEDs.

    One of the problems is getting the right color spectrum output. I don't recall offhand what the correct color temperature is, but I think it's around 6,000° Kelvin. Getting an LED that pure white is a real challenge; as it needs to emit light over the entire visible spectrum.
     
  7. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Plants actually require more than one wavelength to properly photosynthesise, a bit of searching around the unbelievably huge amount of links on the subject will eventually hit a page with simeple answers.

    Any yes, most white LEDs you run into are actually blue with an internal yellow filter to make them appear white.

    Theres another fairly recent thread in these forums that has a lot of research already in it, forget the title line though. These are available commercially so it's been done.
     
  8. mcgyvr

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    Oct 15, 2009
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    I tell you what I just used and you can go from there.. (keep in mind this is for a reef tank application and not a plant growing application)
    I used 2 x Meanwell ELN-60-48D dimmable constant current power supplies. Each meanwell is feeding 12 LED's wired in series. The LEDs I used were 12 x Cree "Cool White" XP-G R5 LEDs mounted on a star MCPCB and 12 x Cree "Royal Blue" XR-E LED's also mounted on a star MCPCB (metal clad circuit board) bolted directly to a heatsink.
    This is for a 30 gallon cube tank and the light is almost overkill. I expect to dim them to 75%. This should allow excellent coral growth.
     
  9. mcgyvr

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    Most "growers" are using LED's in the visible red spectrum..Not sure which.. I've just seen a bunch of videos about LED grow lights and all are red.
     
  10. Wendy

    Moderator

    Mar 24, 2008
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    Actually Red, Blue both, with some white thrown in for visual appearance.

    Here was the latest, with links to earlier discussions.

    300W LED Grow Light
     
  11. Bear_2759

    Thread Starter Active Member

    May 23, 2008
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    I've done some research into the required light spectrums for plant growth, cant remember exactly what the blue one was but red was 660nm and the most common ratio is 1:7 blue:red. I've looked into that allot for grow lights, but that's not my need. this isn't for a planted tank, I will throw in some red/blue at the right spectrum anyway in case I decide to add them later.
    at this stage I'm just looking at light output. one thing that I just thought of, a fluro has a 360 deg viewing angle, led's are more direct light so I would need allot less light output depending on the viewing angle of the LED's I picked.

    so would thru hole not be an option? they're just easier to work with that's all... happy to work with SMD's if needed, done it before it's just fiddly.

    so would I need to match the light output in lumens divided by the viewing angle ratio? e.g. 1500lm/(360/40) -> 1500/9 = 166lm. this is assuming that a reflector isn't used with the fluro which in my case it isn't and that 40° will be what's needed to cover the surface at the bottom of the tank.
     
  12. retched

    AAC Fanatic!

    Dec 5, 2009
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    I have made many a grow light and display light in my time.

    For standard 'grow' light, I use a 3x3 "pixel" or group then repeat that "pixel" as many times as needed to fill the space.

    I use 1 blue to 7 red to 1 orange

    That is my grow light pixel.

    I have done them for orchids which are rather sensitive flowers and very competitive among growers.. For these, I also use a few white cree 1W for "display" mode.

    The sarge is correct about finding the good "white" to display the colors.. And It is rather hard to piece the leds together to balance it out. What I do, is use filters.. Standard glass or plastic colored filters. That will allow you to make a led back board then change the filters for 'pops' of color here and there.
     
  13. marshallf3

    Well-Known Member

    Jul 26, 2010
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    Also seems to me that due to the sheer size of the board required (and the thchant tank) you'd want to build something like this as using a large plate of aluminum drilled out, LEDs mounted with silicone seal then hard wired from the back?

    I could still kick myslef for not jumpint=g on a Home Depot closeout about a year ago. They had two left - an outdoor lighting power supply, 12VDC @ 100A, for $60 each. I don't think they had timers but that's a heck of a lot of isolated power for $60.

    Were I ever to build one I'd prbably use one of the NewEgg computer power supplies when they have them on same, not long ago they had one with 3 x 12V @ 20A, 1 x 5V @ 20A and 1 x 3.3 @ 30A for something like $60 after rebate.

    Currently thy have a +3.3V@24A, +5V@24A, +12V1@20A, +12V2@20A (& a couple of misc ouputs) for $30 with free shipping. If the 12V outputs are electrically isolated it would make a nice bench top supply. The drawback with most of these is although that appears it would give you 700W it's limited to no more than 500W total output draw in any combination. Still, for only $30 shipped, it's useful.

    Nevetheless, when weight isn't an issue I still like being able to pick up 1 KW 480V to 120V industrial contol transformers for $10, give them 120V into the 480V side and you get 30V @ about 8.5A on the 120V output winding. Still wanting to use one of these as a 120 to 480 step up and make a decent tube audio amp out of it. 480V is about ideal for driving 6L6GT or the more modern equivakent high powered audio output tubes, 300 W RMS/channel wouldn't be out of the question given the proper output transformers which are still commercially available as people still build with them. Probably a handful of MOSFETs out there that could also be pressed into play without needing output transformers but biasing MOSFETs to run as linear with little distortion can be a challenge.
     
  14. Bear_2759

    Thread Starter Active Member

    May 23, 2008
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    Hi guys, sorry been afk for a few days.

    @retched: what frequency is needed for orange? I can't remember exactly but isn't orange specifically for flowering/fruit growth where blue/red is for foliage? how many pixels would you have in a standard grow light for a small plant e.g. strawberry? how much total light output have you got? sorry for all the questions, it's just something I'm really interested in.

    @Marshallf3: yeah, I figured if I wasn't using thru hole then I'd just get a massive heatsink the length of the tank and use it as the structural backbone of the system. I'd also need to work out sealing the circuitry as we all know electronics + water don't play nice together.
     
  15. Wendy

    Moderator

    Mar 24, 2008
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    If you were to use something like a baking sheet (which have the edges curled up) you could pour potting compound to seal everything after you have it wired up. Be sure it is working though, no servicing anything after the glue / epoxy is poured.
     
  16. marshallf3

    Well-Known Member

    Jul 26, 2010
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  17. Bear_2759

    Thread Starter Active Member

    May 23, 2008
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    after looking around a bit I think I'm going to build something like this.
    http://smgsllc.com/parts.html

    using the stars will be easy enough. what stars would you guys recommend? I'm looking for the best power consumtion to light output ratio as I'd like to have it save as much as possible long term.

    another thing, the ones they sell in the link above have active cooling, is this needed or would passive cooling be enough? fish tanks already make a fair ammount of noise with air pumps, filters etc etc so would like to make it passive cooling.
     
  18. Wendy

    Moderator

    Mar 24, 2008
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    Heat sinks will go a long way for cooling. Wookie and I are working on a high power LED driver, it will reduce the heat generated by the devices providing the current.
     
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