Self-made LED panel general discussion

But once you have the PAR you still can't compare as plants don't use all PAR equally... Definately much more useful than lumen of course.

Originally Posted by Gastanker

What do you think explains the blue LEDs emitting less lumen than the reds? Shouldn't it be the other way around? And green blows the two away while being in the middle... nvm, that's likely just the voltage difference between the colors.

I've made a little illustration:

The blue dot represents the position of the blue LED's wavelength on the efficiency curve. The red dot is for the red LED.
The precision is not good enough to have an accurate reading but it is OK to get the idea.
You can see that the blue dot has a Y coordinate of about 0.1 whereas the red dot is roughly at 0.3
That means that the blue LED needs 3x more power output to produce the same number of lumens as the red LED. Other way around, the blue LED produces one third of the red LED lumens if the two have the same radiant output. This is why the blue LED's lumen is lower than the red's. In fact, I am pretty sure that the blue LED produces more radiant flux than the red one because blue LEDs are generally more efficient than reds; it is due to the chemical used inside the LEDs.

I'm also realizing that the colors and whites all run at different voltages so even if they are testing under the same mA they are using different amount of energy to produce the varying lumen outputs which like you say have little to do with efficiency.

yep, reds are more likely to run around 2.2 volts whereas blues and whites have a forward voltage of about 3.2 volts; this means that blue and white LEDs chew up more electrical power than reds when at the same current. This is why it is good to keep in mind the radiant efficiency (milliwatts of light emmited for each watt of electricity consumed) rather than the radiant output alone.

Someday they'll make wider spectrum colored LEDs...

Have you looked at reef forums about any of this? Many many DIY LED aquarium lights out there and they tend to be a bit more of an academic group - never once seen a lux meter over there but somehow every other person owns a really nice PAR meter. Aside from them focusing on different spectrum they use all the same gear.

Patrik what kind of "white" LEDs are you talking about? RGB or phosphorous conversion? I'm also curious to know what you know about phosphorous blends and which ones you've heard of that have excellent peaks in the blue and red spectrums that growers like. Do you prefer blue or UV based white LEDs? And what is your opinion on this: Which is better a 2 pc or 3 pc white LED? I think the yellow spectrum in the 3pc is a waste, but maybe the plants can use it. (Gastanker?)

In other words, what I'm really trying to tell you is not to get too hung up on power. You need to do a little more probing to find the right white LED than just using radial-flux and par, though I totally agree that both are very important. Many pc LEDs have a ton of green in them making them not very efficient for growing weed, but somewhat efficient for lighting a room. As far as I know no one makes a white phosphur converted LED that hits peaks in all the spectrum's a grower would covet, though there are some newer phosphors that can get close.

IMHO a white 450m blue diode pc LED can replace blue LEDs without the photo-biological damage that blue LEDs can pose. For the 450 spectrum, most blue-diode based white LEDs will do since that's the spectrum many LED makers like to use, though not all do, so you need to see the spectral output of a white LED to be sure it's what you want to use. Then I would take what your trying to deduce and see how that LED stands up. Here's a spectral output of a 7000K white Epistar. OK for blue, but that's it really. Too much green for me:
White1.jpg

Where's the reds?

I guess what I'm also trying to say to you is LEDs are not CFLs and they shouldn't be HIDs. Good luck Patrik and if I find any good white LEDs I'll let you know.

Originally Posted by patrikantonius

it is good to keep in mind the radiant efficiency (milliwatts of light emmited for each watt of electricity consumed) rather than the radiant output alone.

That's correct, milliwatts is the best we can use

Great discussion going on in here^^^^(I'm no expert/but ill chime in anyways)..............My issue with Led market in general is that these SPD graphs/charts may not be accurate for our applications(growing)/we are not trying to light up a retail store ............The variables involved: LED Bin selection(still unreliable)/heat management(is their any light shift at high temps?)/stable current flow/driver efficiency/counterfeit leds/REAL lifespan/lumen depreciation values(not estimates)/high rh conditions/etc..........Led grow light market is still in its infancy(IMO) and due to Led's rapid progression/evolution in the general lighting industry we need standardization before we can take these manufacturers graphs and realistically apply them to our hobby. LED SPD's put out by the manfctr are under IDEAL conditions, but alas this is what we got to work with atm............I want an LED(module/diode selection) designed/built from the ground up for horticulture dammit!!!

happy growing.......