Reuse LEDs from a LED bulb

I am planning to build a high luminosity lamp to act as a growth lamp during winter for my plants.

For this, I manage to recycle (upcycle?) a big LED bulb with the following inscription:

LED Corn Light E40
Volt: AC 35-265V
CC1: 6000K
Power: 54W


The bulb was not matching my needs as is (especially since it was providing an almost 360 degree light, while I need a directional light source), so I took it apart.

I saved 8 nice aluminium strips with 19 SMD LEDs each. I plan to power these from an ATX power supply, so I have a 12V 15A (probably I should say something like 10-12A to be safe) source.

The problem is that I can't identify these LEDs (I couldn't find a datasheet), so I'm not sure how much power they need. Based on similar LEDs I've seen around, I think 3V and 250 mA per LED would be a good guesstimate. Which means I should form groups of 4 LEDs in series and add a 3/0.25 = 12 ohm resistor per pair, everything nicely stuck to a solid piece of aluminum for cooling.

Are my calculations correct?

Side question: I was measuring the LEDs with a diode meter and it seems they very dimly light up. Also, when touching them in certain conditions, they produce a very dim light (the LEDs being disconnected from any circuitry). Is there any explanation for this?

• "I was measuring the LEDs with a diode meter and it seems they very dimly light up" That's normal... The meter needs to use voltage and current to determine a resistance so it is partially powering the LED. Nov 8, 2019 at 16:32