Why LEDs make bad plant lights (facts + pics!)

[estación seca]

Originally Posted by sesh

...I wish I had seen this website while it was active. Sadly many missing pages now

If you go to archive.org and input the old site's URL, you will be shown a calendar of all the times the archive.org crawler saved the page. Some of those missing pages may still be available.

[naoki]

Do you know some of the efficiency index of these? Or do you have a link? AC LEDs haven't achieved high efficiency yet, which means that most energy is wasted as heat. Even if it isn't efficient, CPU heatsink can easily handle this much heat. If you go passive (i.e. no fan), you need a fairly big size (e.g. 120-133mm diameter pin-fin with 70mm or so pins).

[sesh]

Hi Naoki.

The link is here:
1pcs Hydroponice AC 220V 20w 30w 50w led grow chip full spectrum 380nm 840nm for indoor led grow light-in LED Grow Lights from Lights & Lighting on Aliexpress.com | Alibaba Group

They're supposed to be 50 watt leds at 80lm/watt.

I received the package last evening, and
have scavenged some old CPU heatsinks with fan, but I'm yet to connect with paste.

Will update further once I put them together.

Thanks,
Seshadri

[sesh]

Ok. Pasted the led to the heatsink with conductive paste, soldered the wires (live and neutral), connected the fan directly to 12v dc power. And powered on.
https://i.imgur.com/kj9jOG0.jpg
https://i.imgur.com/WjKxDpH.jpg

It works, so my connections are fine, thats a relief.

---------- Post added at 08:10 PM ---------- Previous post was at 08:00 PM ----------

Two observations,
1. The fan seems to be blowing air into the heatsink. Isn't it supposed to blow the air out?
Anyways, the heatsink was untouchable in 4 minutes, so cooling needs to be resolved.
2. This is supposed to be a 50w led at 80lm per watt. Thats 4000lm. Using a conveter online, I found that with an output of 4000lm and a 120 deg angle, i need to get approximately 5000lux at a distance of 50cm.


I'm getting a reading of 1500lux on my lightmeter app on my phone.

I am thinking I need to understand what "50w" means in the aliexpress product page!!

Thanks,
Seshadri

[naoki]

It does look interesting, Sesh. With this kind of monochromatic LEDs, lumen doesn't tell us much. But if it is REALLY 80lm/W, it is super efficient (I'm skeptical about the number, though). Also, the heatsink seems to be sufficient if it is really efficient. So this makes me think that 80lm/W could be bogus.

The fan should be blowing into the heatsink.

Did you make sure the backside of the LED has good contact with the heatsink? Some heatsinks similar to yours had small round contact area if I remember correctly. If the contact area is too small, it is not appropriate. The thermal paste should be as thin as possible.

It seems to show 50W (53.09W) actual wattage in the photo. Some of these are emitted as light, the others are released as heat (including the loss in the "driver"). With the efficient ones, you can get 50% or more of the input energy as the light output.

[sesh]

Something just occured to me, should i continue in a separate thread, or continue here? I imagine that i am going to need more help by the time I'm through!

[estación seca]

Separate. The title of this thread is wrong for your project.

[sesh]

Ha ha.
My thoughts exactly
Initiating a new one

Regards,
Seshadri

[naoki]

Yes, it is better to have a separate thread. I was curious, so I tried to find a bit more info. Here is a video about this kind of driverless COB by Clive (he has been putting out lots of informative videos).

One thing to note is that these are probably not designed for efficiency. With LEDs, you can't have high output and high efficiency at the same time. For grow light, we use them for long hours, so it is more economical to put importance on efficiency than the total output.

Anyway, please keep us updated (I'm curious how long it will last).

[sesh]

Thanks naoki, estación seca.
I've begun a new post here:
The Windowsill Orchidarium Project