Yet another LED grow light


Joined Apr 28, 2012
I made a panel with small LEDs a few days ago.

I run this from a 12V electronic transformer (1A).

Voltage is 25 volts, since I run many LEDs in series.

There is some point where they heat up too much about at 26 volts. Not they would fail totally, but one string goes off after a while.

Using a MC34063 booster, I run them at 25.7 volts now for a few days, don't get that hot, nothing fails or burns out.

They do however if the voltage is too high.

The current limit is dimensioned so they won't just burn totally and pop useless. But, the actual current is below that.

These panels are not so much useful alone, since you really need 660nm red, the blue is not so important, but 445nm blue is better.

These LEDs are all 630nm.

1W LEDs are far more bright yes, or 3W LEDs.

Really interesting it become when using 10W, 20W, and 30W LEDs.

Don't expect too much from a 630nm panel, plants will start up, but then stretch later, don't flower, or much smaller flowers/fruits.

There should be more red than blue, at least 1:1. You normally should get a saturated, deep pink.

1 Ohms resistors will do nothing, for 20mA LEDs.

If you add a resistor, you increase the voltage margin, nothing else. It is a few volts if you consider turn on, and about 1V to 2V (depends how many LEDs) is the useful adjustment range.

Adding a resistor only will increase the range.

If the actual real current is correct, it can be caused by anything- totally irrelevant.

The tighter you pack the LEDs, the more heat, also the small plastic cases are not good heat conductors. If they are hot to touch, they are already sizzling inside. All what's allowed is them getting a little warm but not hot.

It takes half an hour or so to heat up fully for a panel, also room temp. will affect this.

So, unless you use costant current LED driver, you need to adjust your current well below the limit. Measuring is not so good, since it will show a lower current than real current.

Connecting to a voltage source is never really a good thing, if it is not current limited, it could deliver any current into your LEDs.

I drive with voltage only, but I also use an active current limitation. It is set the LEDs would turn very hot, but NOT burn out under any circumstances, not immediately.

Same for larger power LEDs, I have a transformer which when loaded with 300W or so, will produce a voltage which only will make the LEDs turn very hot, but not burn out or explode.

I do not recommend anything but to use ready-made LED drivers. Otherwise, you will end up with popped LEDs no matter what.

If you like, experiment, but don't say you saw the information on a forum you can just connect the LEDs without resistor. Of course you can. But you need a lot of experience to do it right. And even so, there are cases when you anyway would want to use a ready-made LED driver. For the one or the other reason.

The best is to load the power supply just adequately, not to use a large overdimensionated supply. Many electronic transformers also have an overcurrent limit.

So it would be quite hard to destroy your whole panel.

I have destroyed power LEDs, a few blue one's, and some red one's, which were crap anyway.


Thread Starter


Joined Dec 19, 2011
what does a booster do? increases the voltage of the power supply?
sorry for the silly question, I know very little when it comes to electronics

1W LED vs 3W LED - there is a bit of info about that, I think 1W uses the energy more efficient, 3W provides better penetration

my aluminium plate is just lukewarm - the LEDs are close to the propagator (that generates heat) , there is little ventilation there too. Heat is not a problem now and will be even less of a problem when I move the LEDs from the top of the propagator.

My next setup will be bigger, probably won't need ventilation but I will include a fan anyway.
I will use lots of blue , some red and some white , 3 : 1 :1 I think
1w LEDs should be ok for cacti, no need for the extra penetration given by the 3w ones - in this case

Regarding the colors, it depends what you are growing. This array is mostly for my yucca plant - therefore just for green mass = blue
I have added red only so I hit both types of chlorophyll.
I use them for my cacti for now because at this growing stage the leaves need to be stimulated.

Some info from the research/reading I've done a few years ago, info confirmed by different websites/forums :

"400-520nm: This range includes violet, blue, and green bands. Peak absorption by chlorophyll occurs, and a strong influence on photosynthesis (promotes vegetative growth.)"

"610-720nm : This is the red band. Large amounts of absorption by chlorophyll occur, and most significant influence on photosynthesis (promotes budding and flowering.)"

"Blue light is needed for vegetative growth while red light, particularly deep red in the range of 660, is essential for optimal flower development"

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Joined Apr 28, 2012
Yes it will be very different from plant to plant. Cacti are very slow growing, don't need so much light.

1W are not more efficient than 3W. You can even use 3W at 1W power, or even a 10W chip at 1W.
Large LEDs have more lumens, and are more tolerant to overheating and overdriving.

Yes a booster will increase voltage.

Larger LEDs all need cooling fans. I use 10W, 20W and 30W LEDs, but also 3W chips, and small 4.8mm LEDs.
With cooling fans for each LED, you only need coolers double or 3x as large as the LED chip.

If you want to see results for real plant growth, you need 30W on a small area, and at least 100 for larger plants.

But, if they get some daylight, a supplemental 40W light also gives good results.

I tried white LEDs on radish plants- they mainly build up large leaves, and stretch very much.

They really need 660nm because the light intensity/useable light ratio is the highest. If the ratio is low, plants will stretch to use more light.

Thread Starter


Joined Dec 19, 2011
I have very little real world experience with growing under LEDs, but my understanding is that 660nm is just one of the peaks , isn't that right? and it's for flowers/fruits

So, for the flowers/fruits this peak is the one to aim for - when the plant reaches that stage.

Why would you use 660nm for the other stage? (growing)

Isn't 520nm (blue) for the growing stage?

The cacti as far as I know need a lot of light. I will use about 25 x 1W LEDs for a surface the size of an A4. I would use more if I could fit them, we will see.

I just want a mini cacti garden, I'm not sure if they will ever flower because I don't think they will reach the optimal size in that small pot, but in case this would ever be possible - I've added Red and White LEDs on the plan, so 15 Blue, 5 Red and 5 White.
Red for the flowers, White because some of the light will touch part of the spectrum even if not the peaks.

If it wasn't for the idea with the flowers I would have went all Blue LEDs.

So, are you saying that contrary to the "theory", or at least what some people posted on the internet, it's better to go for Red (660nm) and only some Blue? (520nm)

Btw, from what I know - lumens mean nothing when growing with LEDs , it's just brightness , what the plants need is just sections of the spectrum

This is an article on 1W vs 3W LEDs, not sure if they are right or wrong, but for me, considering my limited knowledge - made sense :

These guys speak about lumens and how 1W are more power efficient than 3W contrary to our perception and common logic.


Joined Apr 28, 2012
Yes 1w vs. 3W- I use 10W and 20W chips, soon even 30W chips. You can't get a decent brightness just with 1W LEDs.

If you want veg. growth, then mix blue/red 1:1, include some 630nm and white as well.

If you want flowering, then it should be 2:1 to 5:1.

Blue should be 445nm, not 460nm. But it is not as critical as with the red LEDs.

Red 660nm makes a very big difference compared to primarily white LEDs. Growth is much better, and plants are more compact.

For your cactus growth, try a 20W red LED and a 10W blue LED (660nm + 445nm). You will get a saturated pink, as red LEDs are not as intense as blue one's.

I use a smaller VGA cooler for the blue LED, and a large 9 dollar cooler for the red LED. Both 12 supplied, directly parallel to the lamp. The blue LED needs 10V, the red one a small resistor (I made one from coils, it's just an Ohm or so).

I could mount many small 3W LEDs, but why? Using one large 20W LED is much, much better.

Thread Starter


Joined Dec 19, 2011
oh got me thinking...but I bought my LEDs already, they are good quality and not cheap! (about £1.5 for one)
It makes sense I guess to go for bigger ones, less work too...but a bit late now..maybe on the next project...