LEDs for orchids

*DISCLAIMER* This project uses exposed 112VAC. I am NOT responsible for any boneheaded mistakes you make with live electricity.

So I decided to make this a separate thread from my environmental chamber.

I've seen in the past where orchid folks have mentioned the using of newfangled LED fixtures from the aquarium hobby to grow orchids. Most balked at the price (which is astronomical at around a grand or so for a high end fixture). I've never heard of anyone using LED lighting for orchids.

So, instead of balking, I decided to build a fixture from scratch.

The fundamentals of LED fixtures are:

-The emitters themselves
-The stars/pads they are mounted on
-A DC power supply capable of delivering enough volts for each emitter's draw
-A "driver" or constant current/current limiting device. This can be as simple as a correctly size resistor or, most commonly, a made-for-LED driver capable of delivering the correct or desired current to the emitters.
-A passive or active heatsink to draw/dissipate heat from the emitters.
-Optics. Emitters are 180 degree spread. Optics are necessary to focus and direct the light.

The emitters need to be wired in series, as does the resistor/driver. The wiring will need to be soldered to the star/pad contacts using rosin core lead bearing solder.

For emitters I went with CREE 3watt high power XP-G LEDs. I bought them pre-mounted to stars. The CREE XP-G is what is found in the newest, highest end reef aquarium fixtures. It has a very white color temperature and tremendous amounts of PAR (photosynthetically active radiation), making it appropriate for plants and corals alike.

For optics I went with 40 degree lenses compatible with the XP-G emitters. This a relatively narrow focused beam, since I am working with a small number of emitters (6) and a relatively small surface area (10 gallon vertical).

For a power supply I'm using a 24 Volt 6.5 amp Potrans PSU.

For now I am simply using a 10 ohm 10 watt resistor as the driver, however this only delivers ~450 mA to the LEDs, and they are capable of running up to 1000 mA, so I will be replacing the resistor with a Buckpuck LED driver capable of delivering the 1000 mA.

I ordered an extruded aluminum heatsink appropriately sized for the top of my tank, some rubber feet for it. I put arctic alumina thermal compound under the stars, and attached them to the heatsink using a single 6/32 screw (this meant I had to drill and tap the aluminum heatsink). The wiring is done with 18 gauge copper wire.

 

Oh, and in case you are wondering, yeah, they are MF'ing bright.

 

Jim, no idea on the lifetime, should be fairly long (years).

The consumption is 3.25 volts per LED x 6 LEDs. Assuming a 1000 mA driver, that's a 19.5 watt fixture.

 

Thanks Forrest,

I forgot to mention, the fixture cost me right around $100 to build.

 

Thanks Ray, great post.