CREE vs 5mm LED efficiency, and other electrical questions

[infection0]

Hi, I'm kind of new to all this and have very little electrical experience. I'm thinking about building my own LED lighting applications and want to find out some of the most efficient ways to do it.

Right now, I'm looking at CREE Q5 emitters vs regular 14000mcd 5mm LEDs. These LEDs take around 20-25mA, I hear. Which application provides more efficiency? Is there a point to using one type of LED vs the other?

Like I said, I'm new so I would appreciate any concerns or tips I might not have thought of.

Also, DX only sells the 14000mcd 5mm LEDs. Any tips on where to find better LEDs for cheap would also be appreciated.

I'm trying to use DC power supplies obtained by salvaging other parts. Some parts indicate 3.7v 350mA and some indicate 3.7v 1000mA, and so on. Will these differences affect the power consumption/brightness of the CREE Q5 or regular LEDs? Or does it just indicate the limit in current I can draw? Sorry, I know this must be a pretty basic question.

And one more thing - should I just be using CFLs instead? Thanks for the help in advance! :twothumbs

 

[alibaba]

I have no idea but I know that folks who do are going to want some more info.

What are you using them for?
How much output do you need?
Do you want a spot type of beam or more of a flood?
Does the color (tint) matter to you?

I'm sure that there are more questions but these might be a good start.
Good luck with the project................

 

[Marduke]

At 20mA or higher, the Cree will be more efficient.

 

[infection0]

I have no idea but I know that folks who do are going to want some more info.

What are you using them for?
How much output do you need?
Do you want a spot type of beam or more of a flood?
Does the color (tint) matter to you?

I'm sure that there are more questions but these might be a good start.
Good luck with the project................

Good point. I am doing some ambient/desk lighting in my room. The lighting needs to be bright enough to read/write over a small area. I'm probably going to put the lighting on my desk and only need enough to illuminate the top of the desk well. A flood would be sufficient for that. Color should be close to white, tints are OK. The output should not be so high as to disturb a sleeping roomate. Here's an example of what I plan to do (assume all the LEDs I use are white) http://www.instructables.com/id/Multi-Colour-Runway-Light/ or http://www.instructables.com/id/Cool-LED-Night-Light/

At 20mA or higher, the Cree will be more efficient.

That is true, but perhaps I need to be more clear. I am intending to use multiple 5mm leds driven at 20mA each (wouldn't this allow for 17 LEDs at 350mA, and around 100 lumens from a CREE?) vs a CREE driven at the same power.

 

[LukeA]

Good point. I am doing some ambient/desk lighting in my room. The lighting needs to be bright enough to read/write over a small area. I'm probably going to put the lighting on my desk and only need enough to illuminate the top of the desk well. A flood would be sufficient for that. Color should be close to white, tints are OK. The output should not be so high as to disturb a sleeping roomate. Here's an example of what I plan to do (assume all the LEDs I use are white) http://www.instructables.com/id/Multi-Colour-Runway-Light/ or http://www.instructables.com/id/Cool-LED-Night-Light/ That is true, but perhaps I need to be more clear. I am intending to use multiple 5mm leds driven at 20mA each (wouldn't this allow for 17 LEDs at 350mA, and around 100 lumens from a CREE?) vs a CREE driven at the same power.

I would use a Cree for better (non-bluish) tint. Specifically a warm white, like 7A.

 

[Jarl]

I would use a Cree for better (non-bluish) tint. Specifically a warm white, like 7A.

Personally I prefer 5A.

The advantages of a cree would be you only have 1. The disadvantages would be that you'd need some heatsinking. Also, 100 lumens will disturb a sleeping room-mate- a pot in series with the LED to lower the current wouldn't be a bad idea, so you can still get more output when you want it.

 

[Lynx_Arc]

for ambient lighting depending on your desk a few 5mm LEDs underdriven could run constantly on your desktop for little power consumption with 1-2 crees for other tasks with proper optics or diffusers to not allow light to go everywhere.

 

[infection0]

Thanks for the tips, everyone. I think I will follow Lynx_Arc's suggestion and have a few 5mms for ambient lighting, and use a well tinted cree for more powerful lighting. I plan to attach both of these systems right under my desk's hutch.

 

[Jarl]

Bear in mind the average bulb throws out 900+ lumens, so you'd need 5 LED's to get the same amount of output with warm tints.

 

[marschw]

Thanks for the tips, everyone. I think I will follow Lynx_Arc's suggestion and have a few 5mms for ambient lighting, and use a well tinted cree for more powerful lighting. I plan to attach both of these systems right under my desk's hutch.

IMO this would make it much more complicated than necessary. When you don't need much light, just drive the Cree at a very low current.

 

[infection0]

Is it possible to drive it at a low current? How would I do that? By controlling the voltage?

 

[SpiritHunter]

2 ways -
1) inefficiently - use potential meter
which controls the voltage

2) efficiently - use a PWM controller
by controlling the pulse width

 

[DM51]

I am doing some ambient/desk lighting in my room. The lighting needs to be bright enough to read/write over a small area. I'm probably going to put the lighting on my desk and only need enough to illuminate the top of the desk well.

Your thread is to do with fixed (domestic) lighting, and we have a separate section for that. I'll move it there now.

 

[LEDninja]

My experience with 5mm LEDs is they dim significantly in 6 months and useless in a year. Stay away.

 

[wild68fury]

My son purchased these and they are nice.

http://www.ikea.com/us/en/catalog/products/20119932

 

[marschw]

My son purchased these and they are nice.

http://www.ikea.com/us/en/catalog/products/20119932

I just bought a different LED light from IKEA, and I have mixed feelings on it. It came with an SSC P4 emitter, which is pretty good, though almost all of the other LED products I looked at in IKEA used either low-power no-name LEDs, or Luxeon K2s. My real problem with the light is that the lens it uses makes an ugly circle of light with a yellow ring around the edge, and wastes a lot of the light since there's no reflector. On the flipside, this means there's virtually no spill outside of the circle of light, which may make it appropriate for use in the OP's situation, with a sleeping person in the room (it still might be a bit bright for that, though). I really like the extra-long gooseneck, however, which is the reason I bought it.

I replaced the P4 with a Cree R2, and the light output increased a great deal, but the beam pattern is now even uglier. BTW, for those who are wondering, the P4 was on a standard star, and driven at 600mA (though, oddly enough, the printing on the star said it was for only 1W; 600mA would be closer to twice that). Note also that the interior of the head, where the star sits, is painted aluminum.

Is it possible to drive it at a low current? How would I do that? By controlling the voltage?

Unlike traditional incandescent lights, you need separate electronics to power an LED without instantly burning it out (incandescent lights, on the other hand, are pretty much just wired directly to the wall current). The standard way to do this is by using a constant-current power supply, since the ammount of current is what determines the brightness. It can be done by controlling the voltage instead, but every individual LED varies significantly in how much voltage it needs for a given current (and therefore brightness), so unless you test specifically each LED and adjust the voltage you're giving it, you'll get hugely varying brightness.

Many constant-current power supplies support a variety of levels of current, and some let you adjust it continuously. A simple, though inefficient, method of making a constant-current power supply would be to calculate the value of resistor you need for the highest current you need, and add a potentiometer (or other type of variable resistor) in series with it to further dim it. There are much better ways, however, and they can be gotten pretty cheaply from sites like DX.

 

[SafetyBob]

For home us ideas, use warm white led's, those Q5's will probably be to bluish compared to all the other lights in your home. Been there done that. Seoul P4s of the generic flashlight modding crowd is also to blue. Warm white the only way to go.

Allied Electric sells P4 Seoul warm white leds for around 6 dollars apiece and they are good. Glued 6 on each 4 foot old flourescent fixutures in the den (uplighting) after they totally burned out. Less light than the flourescents put out, but more appropriate for what they are doing....mood lighting.

I would suggest using advance xitanium led transformers. Think LEDSupply, they were noticably cheaper than anyone else. Order from them alot. Good people. You can get some that dim too.....don't have any installed yet. Mircrodriver9 has 350mA and 700mA power option, so your choice for bright, or really bright.

Look at the Marketplace, I believe Brum is still selling really, really nice optics for the Seouls and Cree lights. Used both optics on both manufactures leds and they are very good. They can channel the light exactly how/where you want it.

Bob E.

 

[2xTrinity]

2 ways -
1) inefficiently - use potential meter
which controls the voltage

2) efficiently - use a PWM controller
by controlling the pulse width

3) most efficiently -- use a variable output-current switching mode regulator, controlled by a potentiometer.

Running an LED at a constant 100mA will be more efficient than running it at 1A with a 10% duty cycle.

Is it possible to drive it at a low current? How would I do that? By controlling the voltage?

LEDs, or for that matter any type of diode, will draw more current exponentially as a function of voltage. This means a small change in voltage can lead to a very large swing in total current draw/power consumption. Simply fixing the voltage isn't always ernough either, as a temperature change can lead to a process called thermal runaway, where resistance of the LED goes down as temperature goes up, causing more power to be consumed, and temp to go even higher in a cyclical manner. LEDs therefore need to be current regulated.

But yes, to answer your question power LEDs can be driven at low current -- and an LED such as a Cree underdriven will be FAR more efficient than a 5mm LED drawing the same amont of power -- as LEDs get more efficient the more gently they are driven.

Many constant-current power supplies support a variety of levels of current, and some let you adjust it continuously. A simple, though inefficient, method of making a constant-current power supply would be to calculate the value of resistor you need for the highest current you need, and add a potentiometer (or other type of variable resistor) in series with it to further dim it. There are much better ways, however, and they can be gotten pretty cheaply from sites like DX.

I find it's often quite difficult to find pots t

 

[Mr_Light]

The following lamp seems to be a pretty good deal at it's current price. It uses a 1 Watt Lux Star that is very easy to replace. I have bought and modded a few with CREEs and SSC P4s. The neck is a little weak for the weight of the head, but in general it works fine. Just a an option.

Nuwai 1 Watt Luxeon LED Desk Office Lamp $15.95
http://www.batteryjunction.com/f5fx-dlx181.html

 

[infection0]

3) most efficiently -- use a variable output-current switching mode regulator, controlled by a potentiometer.

Great. Any idea where I can buy one of these babies? (DX? I couldn't find any potentiometers there)