LED lighting Setup from scratch

[saikumar]

@saikumar - I tend to disagree that at 2W you will get high efficiency. Whats the point of buying 3W LEDs if you want to run them at 2W ? In my view , a 3W LED clearly needs a 1A driver.

Hi Joyce,
I agree to you, no doubt using a 1A will be best to use up the LED. I said 2W because of 680mA which Gujrap has procured(3X.68~=2W)

Regarding the efficiency it should be on most of the data sheet. And by efficiency I meant lumens-per-watt and no other parameter, from what we have gone through the thread
at 1W it gives 109lumen, at 3W, gives 220lumen. so thats109lumen/W -greater than- 70lumen/watt. Thats the point I wanted to make.

[juanico]

@Juanico...a driver rated at 6-24V implies that if the forward voltage of each LED is say 3.0V , you can put 8 such LEDs in series. If there are 6 LEDs, then the voltage required to drive all 6 would be 18V , well within the range of the driver.

somehow this topic cough my interest and i am quite busy searching the net in order to understand the basics of leds.
so far all sources mention, that overpowering a led by too much voltage will lead to higher temperatures, which leads to more current flow, which eventually destroys the led one by one.
so they all recommend using resistors for limiting the voltage according to the need of the led...but this is only possible if you have a constant power (voltage) supply.
furthermore NOT using a resistor has the effect, that some led are brighter than others, due to production tolerances...and also eventually to breakdown of the leds.
(at least as far as i understand the internet sources).

1. please help me with my calculation:
power source: 12V, 1A
LED: 3 x 3.25V led, 1A each.
Connected in series= 9.75V, so i have to kill 2,25V by an resistor (3W, 2.4Ohm), right?

2. How do you calculate how many 3W led you need for a tank?
Just by assuming that they are approx 30% more efficient in terms of lm/W than T5? so, 24W T5 would be replaced by 17W LED (=approx 6 x 3W leds)?

[saikumar]

Hi Juanico,

There is one basic thing withled drivers, i.e. Constant current. Something an SMPS or adapter can't give you. Same reason why people don't use it directly. Led difference ll be negligble for same part number, with belief that somany are in use on forums and run years. Agree on overpowering, should be avoided.

Now you know adding a resistor will not help,but some supplies we have voltage adjusters, not sure if Gurkap has, though it says 6-36v? Best thing is to compensate with a similar led, driving less than 3.25 shoulnt be issue, but adding resistor will be.

calculations on your second point are just fine, but for the assumption.

[apuda2010]

@Juanico....what you read about using resistors to drop the voltage is true for regular dome+lead LEDs available off the shelf.

High wattage LEDs work a bit differently because their intended use is different. For example, 10W LEDs are typically used in street lighting. The drivers used for such high wattage LEDs are able to provide the correct voltage for every LED in the circuit as long as the total voltage does not exceed the maximum. Therefore, these are not constant voltage drivers but variable ones. This allows the user the flexibility to change the number of LEDs in the circuit in real time. So, to answer your question , yes, you will need to kill the balance 2.25V if you use a constant voltage driver. But if you use a 9V-20V driver, you do not need to.

I went from 148W of T5+T8 to 42W of 3W LEDs. Thats an efficiency gain of nearly 70% purely in terms of power consumption. This happened because the CREE XP-G pushed 345 lumens at 1A current. This works out to roughly 116 lumens/W, whereas a T5HO 24W 2 feet tube should be able to give you anywhere between 60-80 lumens/W. If you move from T5 to an LED with less than 100 lumens/W , I do not think the switch is worth it. A T5 gives you strong sharp light with low glare and flicker free operation. The T5 drivers are also programmed for soft start which ensures that the light reached peak intensity gradually.

[khamba]

but some supplies we have voltage adjusters, not sure if Gurkap has, though it says 6-36v? Best thing is to compensate with a similar led, driving less than 3.25 shoulnt be issue, but adding resistor will be.

The driver I got does not have the dimming option. Got this from Lajpat rai market. There was a 60W(shopkeeper said I can attach 20 3W LEDs) 1.4A driver also available, again with no voltage adjustment. I'm guessing 1.4A will be overkill for the Seoul LEDs?

[saikumar]

Hi Khamba,

This a trick for your to remember, buy the driver which has amp rating in multiples of current rating of your LED.
Now suppose your Led max current is 1000mA(1A), meaning 3.25X1000=3.2W
So, you better choose drivers with 1000mA(or appx 900mA) or 2000mA(appx 1800 or 1900mA) or 3000mA(appx2800 or 2900mA0 etc,

Do you get it now?
Or you can always run your LEDs at 0.75A, giving 3.25X0.75= 2.275, not full throttle but still glows, try and operate it once, you might be satisfied with it instead of thinking too much of calculations.

(hint: why multiples? because you can add your LEDs in parallel, and current gets halves in two strings)


Hope it helps.

[juanico]

(hint: why multiples? because you can add your LEDs in parallel, and current gets halves in two strings)

yes, theoretically yes.
but again due to tolerances some string might glow brighter than others...have seen this in one setup in delhi...the distribution of light was bad, and the brighter leds won't last long.
unless you operate them with a resistor, or like you suggested by an additional led which drags dawn the available voltage.

[saikumar]

Hi Juanico,
Well, may be buying stuff of a reputed seller ll help? Or packed box? Because atleast then we ll know they all are same.
I ve been running 12 edisons(recently +4some xyz) for year and half no blow offs, no non-uniform light.

Id say take a mini jump, then try for a leap.

[juanico]

Hi Juanico,
Well, may be buying stuff of a reputed seller ll help? Or packed box? Because atleast then we ll know they all are same.
I ve been running 12 edisons(recently +4some xyz) for year and half no blow offs, no non-uniform light.

i have no own experience with led yet, just referring to experiences in the net and the one example i saw at a friends setup.
i'll try for sure...just would like to understand the basics before buying/doing it

maybe these negative examples were related to no-name-china stuff

[juanico]

just an update:

together with Khamba we did some LED hunting in baghirat palace the whole saturday.
after visiting 5 million shops we were able to get edison 3W led for Rs48, according to data sheet they produce 120lm/W at 350mA and 210lm (70lm/W) at 700mA

i made a 3x3W lamp for a nano to replace a 11W PLS. it makes a nice light, but am not sure, which one is brighter...the PLS or the LED