Builing an RGB LEDs lamp: which LEDs to use?

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daggett

Newly Enlightened
Joined
Mar 17, 2008
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Hello,
I'm new here, and did serach for a post on the subject but couldn't find an answer, so here is my findings and questions, sorry if I missed some post that have the answers :)

I'm on a project to build a color changing LED light. The light will be used as an ambiant light source, so it must be quiet bright. (I've tried with an array of 5mm LEDs but it makes it only decorative, it can't be used for lighting).

I've already done the PWM controller part with a PIC microcontroller, and now I'm on the LEDs part.

I've bought some IP122 transistors which can support 30W of power for each channel and some 5W ceramic resistors and heat sinks. The lamp will be housed in a white glass globe from Ikea named "Fado" (20 or 30cm diameter).

There are 4 channels: Red, Green, Blue and White.
I added a white channel because it could fit in the PWM generation and because I never had real white with RGB colors.

I've done some digging over the internet to try and find which LEDs I can put in my lamp, but I couldn't decide.
Here is what I found (prices between 5 and 8 Euro for 1 LED):
- 3W Prolight RGB LEDS 100Lumen (this one is 13 Euro but there are 3 in 1)
- 3W Prolight Red, Green and Blue LEDs 60Lumen for Red and Green and 20 Lumen for the Blue one
- 3W Prolight White LEDs 50 Lumen
- Luxeon K2 130Lumen (Red, Green) and 35 (Blue)
- Luxeon K2 White 140Lumen
- Luxeon Rebel (R65, G130, B27)

There are also the 5Watt but they are quiet expensive...
So what are your advices, I understand it will be a balance between price, brightness and heat generation.
But what should I use? 1 or more LEDs for each color (I thought 2 per channel) or several RGB LEDs (I thought 2 or three of them plus 2 white LEDs) ?
Which one? Which power rating ?
Thanks for your help and expertise!
 
some other options to consider would be:

(1) an array of osram Power Toplight LEDs, which at between 0.25 USD per LED for warm colors, and 0.46 USD per LED for whites and cool colors, and efficiency up to 50+ lm/watt depending on color, may be a good solution, especially heat wise.

(2) Edipower 4w RGBA emitter:

http://www.edison-opto.com.tw/products_detail.asp?category=1&cno=100

about 10.00 USD if I remember correctly.

You would probably have to order it directly from Edison Opto.

(3) LED Engin 10w RGBA emitters:

http://www.ledengin.com/ledengin_products.html

available from Mouser.com. Something like 30 USD each. But they make a lot of light, so might be worth it. Looks like they haven't arrived yet though.

How are you mixing the colors, optically? Is it important to have multiple colors in one part, or can you live with separate red, green and blue LEDs? Do you need to have access to both anode and cathode of each color in a multi-color LED?
 
What about the seoul p5 rgb?
Good luck and be sure to post pictures!
 
I have used DX RGB leds witg good results. They has comon ( - minus) i drived it via PWM and p-channel mosfets) offcourse it would be easier to operate with common + , then it is possible tu use amc7135 chips as drivers and no need to calibrate resistors to get "the right balance" between rgb colours.
 
hello,
Thanks for your answers:
@spun: I took some ideas from your first link for the Z-Power LED. But I didn't find any data about how many lumens the LED you suggested (DX RGB 3W) can give (didn't find this on google or led-museum), do you have some documentation about this ?


@snarfer: what do you call Osram Power "Toplight" LEDs ? I can't find any "Toplight" reference. Is it a "type" of light or a reference of an Osram product?
For Edipower LEDs they can do the trick, I will keep this reference.
LED Engin 10W RGB seem to be what I'm searching for, but are really expensive, and 2 of Prolight 3W seem to be as bright as them.


@knabsol: Seoul P5 RGB 3.5W can do it, they are less expensive than Prolight RGB, but are rated as 78Lumen (Prolight are rated 100Lumen for 3W). But I guess it might be equivalent. Prolight also have a blurred lens, so colors can mix.
And yes, be sure I will post pictures here!

@MatajumotorS : I choose bipolar transistors because mosfet seem to not support well high power, but if you have some power mosfet references, can you give them please ?
Concerning the DX RGB it seems that I won't be able to use them because I designed the circuit so the cathode ( - minus) must be separated, plus I can't find any Lumen rating for this LED.

So the conclusion seems that usable LED lighting is still very expensive, but LED decorating is affordable.
I think I will go for RGB (no 1 color LED): Seoul P5, Led Engin or Prolight... but I still can't make a choice between them, what will be the best ?
Is the choice of RGB instead of mono-color LEDs the best ?
 
the dx rgb arrived yesterday. definitely common anode(+) and different than the picture they have. dx is not the land of documentation so who knows on the lumens. i'm running them from 100-150ma and that'll be plenty bright for my lamp. the red is a tiny bit orange but fine for what i'm doing. those RGBA leds snarfer mentioned look like the ticket for fine color work.
 
sorry i mistyped. in fact i was referring to OSRAM Power TopLED. My brain must not have been working. These LEDs are not high power (max continuous current something like 50mA depending on color), so you would need a lot of them. Also for some reason their green, blue and white LEDs are quite a bit weaker in lm per watt, so in order to mix these and get a good white you might have to do some experimentation.

I did a quick search for "prolight 3w rgb" and came up with this:

http://www.led-bulbs.com/eShop/10Browseprorgb.asp?Category=Prolightrgb

Looks like they are selling a six leg version, and have a datasheet available for download. The datasheet says 32 lm red, 55 lm green, 13 lm blue.

So that is a bit less than 1/3 the light output of the LED Engin 10W RGBA.

Compare that to three rebels mounted on a star. At 350 mA you would have 40 lm red, 80 lm green, 23.5 lm blue, for total about 6 dollars plus the cost of the star. At 700 mA, if you believe the data sheet, it would be 85, 145, 48 respectively, so comparable to LED Engin if you add amber. Unfortunately you would have to wait two more months, minimum. I know because I have had those exact rebels on back order since January, and Future just told me it would another 8 weeks before they could deliver.

And then the next question is how you want to mix in the white. wouldn't it be better just to use an RGBA LED?

Too bad there don't seem to be any MCPCBs or optics available for four rebels, although there are some lenses for five.

Finally, I don't understand what you're talking about when you say that MOSFETs don't support high power. Are you serious?

EDIT: now I realize that you are talking about mains power. Try IRF840B for a cheap MOSFET. Good up to 500 volts. I am curious how you plan to design the power supply for the MCU.

After typing this I just checked your original posting and looked at the Fado lamp. Now I understand what you are really trying to do. Consider that Ikea suggests using a 20w energy saving bulb in this light. This would be about 22 lumens per watt, so total of 440 lumens. Take that as your starting point, and keep in mind that this is a thick frosted glass enclosure, so color mixing isn't much of an issue.

Personally I would just go with whatever costs the least, and/or requires the fewest parts. I don't see any advantage to using an RGB LED. The 10w RGBA could be pretty good if you were only going to use one. Fewest parts. Designwise this is a nice idea.
 
Last edited:
daggett said:
hello,
@MatajumotorS : I choose bipolar transistors because mosfet seem to not support well high power, but if you have some power mosfet references, can you give them please ?
Concerning the DX RGB it seems that I won't be able to use them because I designed the circuit so the cathode ( - minus) must be separated, plus I can't find any Lumen rating for this LED.
Click to expand...

Mosfets i have used was IRLML2502 20V 3A (for common +) and IRLML5203 30V 2A (for common -) . They are in SOT-23 package. Using 1W (350mA) dies more than enugh .
DX RGB leds seems like ProLight leds 4-pin 3W leds (3x1W).

P.S. why do you think that there are no high power mosfets? you can use even this IRF3205 for high current PWM switching... but for 5V aplications it is better to be Logic Level Mosfets.
 
Last edited:
spun said:
the dx rgb arrived yesterday. definitely common anode(+) and different than the picture they have. dx is not the land of documentation so who knows on the lumens. i'm running them from 100-150ma and that'll be plenty bright for my lamp. the red is a tiny bit orange but fine for what i'm doing. those RGBA leds snarfer mentioned look like the ticket for fine color work.
Click to expand...

It seems to be a lottery :twothumbs i wanted common + but i got common - :scowl:
 
OK, thank you all, I made my choice:
- 4 Seoul P4 3,5W LEDS : Red, Green, Blue and White (it makes 60 + 100 + 20 + 120 = 300 Lumens typ. at 350mA, but those LEDs can support up to 1A current: 108 + 182 + 38 + 240 = 568 Lumens !!!)
- an RGB Seoul P5 (3W) LED (for testings, if it's OK, I 'll buy more to light up my living room or bedroom with a dozen on the ceiling)

I choose Seoul because it seems that they are the most efficient LEDs at that time (twice the efficiency of Luxeon K2). So it means the same amount of light as K2 but less current and less heat (it seems that they are also cheaper).

RGB high power LEDs (> 3W per LED) are much more expensive, so the best is to buy separate LEDs (my "Fado" lamp will mix the colors together, so no worrying about separated colors).

@knobsol: this is one of the projects I mixed up with mine, but I started this project 3 years ago, so there weren't that much examples at that time, and power LEDs where REALLY expensive then and not that efficient. But now it's time to complete what I've planned so long ago!

thanks for your advices and links, I'll post some pictures when it 'll be finished.

bye for now.
 
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