What to ask when your considering buying RGB LED Pixel strings

Discussion in 'RGB Lights - Intelligent Pixels and 3-Channel RGB' started by mrpackethead, Jan 10, 2011.

  1. mrpackethead

    mrpackethead Full Time Elf

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    Hi Folks, theres a lot of discussion going on about RGB LED Pixel Strings at the moment. And when that happens its sometimes hard to distinguish fact from fiction.
    So i've put up some basic questions that you should ask before you consider investing in some. Later this week, i'm going to post some technically focused diagrams and discussions for those who want to dive in a bit deeper.


    (1) Constant Current or Constant Voltage

    The light output of LED's is largely controlled by the amount of current flowing through them, and not the voltage applied across them. In order to make all the LEDS in the string glow with equal intensity its important that the current flowing in each led is as close as possible. This is achieved with a constant current controller, but not with a constant voltage control, where the current is set with a current limiting resistor. No string is exempt from voltage drop, ( ohms law always applies ). Measurements of the light output in a string of constant current leds typically show show variations of less than 5%. We have seen variations of more than 40% in constant voltage controlled strings. Why doe sit matter? Well, the big reason is that when you go to mix your colours, different leds will behave differently from each other, ie, some leds might look "pink", and some "purple" when told to do the same thing. ( and don't' be fooled about arguments with higher supply voltages, ohms law still applys! )

    THe supplier may not be able to tell you this ( they may not know ), but find out what controller IC the strings using, and post it back here; most IC's are well known now and we can help you figure it out.


    (2) What is the light output?

    A technique that has been employed by some manufacturers to get over the voltage drop issues in some strings, is to simply reduce the current flowing in the strings.. ( halving the current will half the voltage drop ).. However lower currents result less light coming out of your pixels.. In effect what might seem like a bargain isn't because you'll need twice as many leds to get the same light levels..


    (3) How energy efficient is the set up?

    This is a major differentiator among led strings that i'm seeing. Wasted energy is 99% lost as heat. And heat and electronics is typically bad. Every time something heats up it expands, and when it cools it contracts. Expand Contract Expand Contract, over time that results in thermal stressing, and thats the major cause of failures in electronics.. Every led pixel system is to some extent going to waste some energy.. However the more waste heat the worse things are.. It doesn't end there though.. Less efficient led strings mean you need bigger DC power supplies.. ( and do you want to buy bigger more expensive power supplies simply to run your little led heater? At least for me i'm building LIGHTING displays not HEATING displays..

    I can be a little hard to establish the system efficiency, without some technical data or measurements.. What you want to know is how much energy is being used in total, and how much energy is being used to just drive the leds.. The difference is "waste" because its doing no useful work, and ratio between the two is the efficiency. A simple way to spot potentially inefficient systems is this.. (and i know i said i wasn't got to go tech, but )… For single LED pixels, you want a supply voltage that is close to the Forward voltage of the LED itself.. ( thats 1.8V for Red, 3.2 for Blue and Green ).. The reality is you need a bit more voltage than that to keep everything working properly.. but not lots more.. Generally speaking the waste energy in the system is the ( supply voltage - led forward voltage ) x operating current of the led. Good string design requires a number of factors to be considered. Simply optimizing a design for one parameter is likely to result in poor performance overall. ( please note that there are advanced controllers, that can use higher voltage supplies, to drive leds, which don't' waste all this energy. these are typically used for high power leds ( >1W ). These use inductors and capacitors and complex switching arrangements to achieve this.. Typically low power led pixel strings ( like the ones we commonly pop up ) are just a simple transistor based current control or transistor switch. )


    (4) Build quality?

    Theres some major differences between the way different strings are being manufactured. You really need to establish how well your strings are going to last. Also the quality of the components in the actual pixel varies widely. There are several chipsets that commonly being used which are manufactured in factories that have very very poor Quality Control, and the failure rates are high. The actual manufacturing process's vary between suppliers.. Some manufactures will claim waterproof to IP68, but the first shower of rain will kill them. My suggestion is before you dive into spending hundreds or thousands of dollars, get your self a sample of their product and establish for yourself the build quality.. If your supplier won't supply you a sample, then you've got to ask why don't you?


    (5) Warranty, Support, Backup and Spares?

    The answer to this will depend entirely on how much risk you are prepared to take, and how confident you are of sorting things out for your self. The old saying is true " you get what you pay for "



    Disclosure: I do this stuff commercial for large-scale displays. The number of led strings that were out on display in 2010 was many more than you can count on your fingers and toes. Our target market is the prosumer and commercial markets, with plug and play solutions. In no way am i trying to discourage or scare the hobbyist, in fact i'm encouraging you to jump in big time. In posting this, i hope you are better equipped to ask your suppliers some key questions about their products so you can make a better informed choice.
     
  2. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Some very good information there Andrew.

    With DIY lights from China compared to prosumer and commercial options there are many different advantages and disadvantages going either way.
    The prosumer/commercial light supplier will have warranty, customer support and a product that has been tested extensively but this does cost money, so if your not confident in doing your own repairs and/or modifications then this may be the best option for you.
    Going down the DIY path and sourcing your lights from China normally will not have the same level of quality, warranty and support but on average will be 1/2 the price. So if you feel that your open to a bit of DIY then you can save a lot which means more lights and you do get the support of the community with many members already using these lights.

    So your comfort levels, knowledge, skills and budget will determine which direction you take on, both will give you the same results, Colourful Blinky Flashy.
     
  3. AussiePhil

    AussiePhil Dedicated Elf Administrator

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    Andrew,

    Good set of questions and I'm sure others will surface.

    Re Build Quality.

    This is something that was discussed lot's last year be people getting into this for 2010 and even at the hobbiest level is something that should be taken seriously.

    I have around 500 pixels that i would call samples though they were purchased, about 60% of them will never be used outside as they would not be considered even vaguely water resistant without dipping completely into some sort of plastic coating.
    It took this many before I found ones i would use.
    Even the ones i used for the megatree required zip ties to be used to assist with sealing. For hobby use were you have some spare time this is just time consuming rather than truly painful. If you plan to use thousands then it is definately a factor you should take into account.

    Whilst a failed pixel can be cut out and replaced, the time it is failed in the string then every pixel (node) after the node will also not work, this could mean the entire string if it is one of the first nodes.

    So ask yourself these questions.
    1. Just how water resistant is the string i'm looking at.
    2. Just how much work (time) will i need to spend to make that soft pastic node waterproof.

    Phil
     
  4. OP
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    mrpackethead

    mrpackethead Full Time Elf

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    No eddy, i disagree. Buying poorly implemented pixels, will give you a pile of drama that may result in you not having any blinky flashy.. Price is not the only factor to consider here entirely. You can buy well designed pixels that need some DIY love to bring them up to speed, at low prices from Wu and Co. You can also buy some other cheap pixels from Wu and Co, or some other guys that are inherantly flawed in their design.. And no amount of DIY love will make them good for much at all...
     
  5. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Another question you could ask is if the lights have any form of UV protection, many dont and this may be a factor for very hot dry climates, The longevity of the non UV protected lights is still being determined but with some of my lights i have seen some discolouration, they still function well and are not brittle, but then these are only the lights i had on hot black roof tiles that really showed any UV deteriation.
    Also remember that there are some different issues surrounding different types of lights like using RGB strips and modules compared to using RGB strings, each has their advantages and disadvantages based on how you plan to mount and use them
     
  6. fasteddy

    fasteddy I have C.L.A.P Global Moderator Generous Elf

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    Sorry I didnt relize we were only talking about strings (I should read the title better), but these questions are great questions when also sourcing strips and modules.
    I have used lots of RGB modules and strip and when i compare the strip i used to a commercially available strip for the price I know which direction I will take as the differences were minimal and the performance was the same. In my video i use CCRs for the top gutter and I use the 6803 strip for the bottom gutter, when i asked some light enthusiest if they could spot the difference, they couldnt. The difference for me was a product that yes did appear to have a slightly lower quality than the CCR but when performing the outcome was the same but with a massive saving.

    Pixel string themselves have their own issues regarding weatherproofing and how you mount them, i had 200 2801 UV protected strings in my display and I did not loose one of them and they stood up better than my expectations. I did also make sure that i didnt have them hanging in a way that would allow water to easily seep in.
     
  7. riri7707

    riri7707 Full Time Elf

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    This post is very interesting and it reflects perfectly the stage where we are today with the RGB strings.
    Thanks to all for your contribution and explanations.
    It becomes more and more interesting each day... :)

    My very small experience on that (less than a year), learned me how difficult it is to navigate in this jungle, speciallywhere 99% of the strings comes from CHINA, and the chips too...

    And i'll don't talk you about Chineese products between MAINLAND and HK zone; it's not the right post here for that...

    But the great thing is a lot of members shares their knowledge, experience, thoughts trough their hands-on and feedback.

    As on each Hobby, every one can go to the Rolls Royce of the products, middle range and basic ones.
    All depends on the level each one will go, and the budget to inject in this Hobby ...
    So technology, improved products, self-made and baddest experience is part of the game.
    Hopefully, we are not alone and members always give their feedback about this pixel or other one more robbust, UV protected, waterproof, etc...

    As this year will be really the year of RGB strings/strips/pixels/modules displays, i think we will have a lot of interesting things to share here...

    Personnally, i don't' like specially all the manufactured display devices, where we need just to buy and plug. It's more funny to buy basic things and modify them to implement your personal touch.

    What is sure today, they are common elements on the displays ( SMD 5050 LED / different chips).

    Just about 5050 SMD, you can fall in a nightmare just about the quality itself of the component (different manufacturers, pricing), where 1cts can make all the difference....

    Let's continue to share our experience here as we have the chance to have high level members who shares their professional knowledge, middle ones who share their hobby experience and new ones who takes the train running since few months on this technology and wants to learn in view to build their next display.

    So for sure we need strips, strings, modules, original creations and the "brain controllers" to manage that.

    Henri
     
  8. wjohn

    wjohn Apprentice Elf

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    Andrew,

    Which pixels from "Wu and Co" do you recommend, and which pixels from "Wu and Co" don't you recommend.

    I am happy to invest some DIYC love to economical pixel investments.
     
  9. Bridgette

    Bridgette Apprentice Elf

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    I dont mind a little DIYC love but my main priority is longevity, too big an investment to be throwing heaps away and cutting and shutting all the time

    Bree
     
  10. TimW

    TimW Full Time Elf

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    And who are these "other guys" of whom you speak? :)

    The other point that might be worth taking into account when choosing pixels is the protocol.... not all the protocols/chips have the same capabilities. Some have different intensity ranges (5/8/9 bits etc) - some are slow refresh some are fast, some are, well, a challenge to work with (HL1606 anyone?... and those GE strands seem more trouble than they're worth!!)


    Is there a lack of consensus that WS2801 variants are currently the 'stability leaders' in this space? Has anyone had bad experiences with them (apart from Jim's different lengths problem and the need to apply TLC to the waterproofing... and some UV discoloration?)

    Haven't heard much problem with the 6803's (properly waterproofed) either?
     
  11. OP
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    mrpackethead

    mrpackethead Full Time Elf

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    Well, to be honest, i've only found one actual source for this TM1804 based 12V pixel string, thats Ray Wu online. Theres a project running on another community right now, but they won't say what they are using, but everything points to a TM1804. And they hav'nt actually released anything yet so thats all still "wait and see pudding".. All the normal sources for this stuff are not making it.. If it was such a good idea they would be on it like a rocket.
     
  12. wjohn

    wjohn Apprentice Elf

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    How about 2801 recommendations?
     
  13. AussiePhil

    AussiePhil Dedicated Elf Administrator

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    John,

    2801 Recommendations

    Responsebox ones - ie MPH

    I used Onumen ones - bought direct, they needed a little love but stood up very well.

    Phil
     
  14. Gary Martin

    Gary Martin New Elf

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    I have just started experimenting with some RGB strips (CCR clones) from Ray Wu. The first two sets I got in I am just attaching to Ray's 6803/DMX adapter (it's the only protocol bridge I can get atm). I am seeing a few quirks that I wanted to check with you guys to see if this seems normal.

    First off, these seem to be coming up as BGR leds on his controller via DMX instead of RGB. Is this normal? His simple controller doesn't have any way to fix that so as to make the sequencing software happy.

    Secondly, running the test firmware in his DMX controller, there are two pixel sections on one strip that consistently don't respond right. The entire strip will be red while those two sections are a different color. They seem to correct and work okay for a while but then get off again. Does that sound like bad pixels in the strip or bad memory in the DMX interface?

    Thanks in advance!
     
  15. riri7707

    riri7707 Full Time Elf

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    Hi Gary,
    For the problem of RGB/BGR can be also GBR etc...
    This comes from manufacturers at it seems, even if it's the same protocol, the RVB led are not wired the same on output of embedded chip.
    So you need to implement the order as your strip was manufactured on LSP or VIXEN.
    Third party software using standard controller offers you the possibility on settings to change this order...

    I recommend not to begin to mix a lot of different strips/strings from different sources as you will encounter such problem and in some cases, you will not have the possibility to run them on same controller.
    Take care..

    For your second problem, can be faillure in the strip, the data and clock are too much perturbed and doesn't communicate the right info .

    Can also be a power supply problem who is not enough strong.

    Normally, if there is a problem on the strip, you need to investigate around the first one pixel who is wrong...

    In bad case , cut the faulty pixel and chain the rest of the strip
     

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