I wanted a bright light to help start my seedlings in the spring. There are two variation to this project, one with a heat sink and one without. The photos are for the heat sink version since that is what I made.



  • Strip Connector($2.68 if you are scared to use a soldering iron)
  • Cookie Sheet ($7 at IKEA for a "Heat Sink")
  • Dimmer ($5 if you want the ability to adjust brightness/heat of the LED's)

Step 1: Cut, Measure, and Attach.

If you are going to attach the strips to the humidity dome of your seed tray. Measure out the strips to fit inside the dome with some space for wires to connect the strips.

If you want to use a heat sink, then use a cookie sheet that fits on top of the humidity dome. Then measure and attach the strips on the cookie sheet. (Its warm where I live all the time so the heat sink helps dissipate the heat generated by the diodes. It also helps them last longer, running at full brightness I measured them at 60C.)

Cut the strips along the copper "cut points".

Attach the strips using the double sided tape that it comes with.

Step 2: Connect Lights

If you are opposed to getting a soldering iron then use some connectors to get all the strips attached. Then when you wire up at the end be sure to attach the positive (red +) on one end of the series and the negative (black -) to the other end. This will ensure that all the LED's will be similar in brightness. If you are using a full 5 meter (16.4ft) strip inside that dome the ones on the end will end up being dim if you don't.

If you can use a soldering iron then grab some scrap wire (at least 22AWG) and connect all the wires on one end to the positive and the other end to the negative (see the photos). This will equally distribute the power to every strip.

Step 3: Adjust & Time

If you want to adjust the brightness of the lights you can get one of these. I like using one for making the light a little less bright for seedlings then ramping it up before they go outside (mimicking the seasonal change).

Plug your power supply into an outlet timer. Set the schedule between 10-16 hours a day depending on what you are starting and where you live.

I live in Phoenix where we plant in February. So if I were to start seeds in December would choose 11 hours of light, because that is the amount of light hours in February here. The further north you are the more hours you will need to compensate for the late start. June seed starts in Phoenix would be 14 hours.

<p>Sorry, but you are mistaken: &quot;I live in Phoenix where we plant in February. So if I were to start seeds in December would choose <a href="http://aa.usno.navy.mil/cgi-bin/aa_durtablew.pl?form=1&year=2015&task=-1&state=AZ&place=phoenix" style="">11 hours of light</a>, because that is the amount of light hours in February here. The further north you are the more hours you will need to compensate for the late start. June seed starts in Phoenix would be 14 hours.&quot;</p><p>Seedlings don't vary in their light needs by latitude.<br><br>I run seedlings under 18-24 hr days, as they actually don't care about hours of darkness.</p>
<p>Thank you for your opinion, I still find my rule of thumb works best for me.</p>
<p>I think the cookie sheet would be better because of the mass - If it gets really warm, maybe a small laptop or video card cooling fan will dramatically improve the cooling. BTW, that may even improve air circulation inside the container if controlled properly. I don't know much about how that affects plant growth and humidity. </p>
Ya, I have considered a small cooling fan but with it placed on top it seems to dissipate the heat fairly well. I am not very experienced with fans in growing room setups. Maybe someone else can chime in, I would love to know how that helps/hurst the growing.
<p>With seedlings, I open them up 1-2 times per day and tweek them lightly with my fingers (or blow on them) to help strengthen them. An internal fan (circulating) does the same for larger plants. No point in an exhaust fan for seedlings, as they and their media both tend to suffer water loss rapidly, and they use little CO2, thus a complete air change twice a day is sufficient.<br><br>As far as heat from the lamp, if the temperature under the lamp is under 100 F you're probably o.k., under 70 F and you may have trouble germinating most plants.</p>
<p>A fan is a tricky one... Having a fan will circulate in fresh air, which will decrease the humidity and therefore increase the rate of transpiration (water loss from the leaves). This is excellent if the plants have access to minerals dissolved in water ( as in a hydroponic system),as it draws up more minerals to the plant, but if watering is neglected then they will wither more quickly.</p>
<p>An alternative to the dimmer (generates even more heat) - a PWM controller is about the same price.</p><p>search ebay for: &quot;12 v Pulse Width Modulation PWM&quot;</p><br>
<p>Very nice 'ible! ( and also your new one with reflective foil).</p><p>Just a small observation - you must mean heat sink, not 'heat sync'. 'sync' is usually used these days as a slang short form for synchronization, and 'sink' is as in kitchen sink, something that drains off and disposes. In this case heat sinks help remove excess heat and dissipate it by convection. </p><p>I don't know how efficient these specific LEDs are, but with 72W being pumped in, you do want to get rid of any energy that remains unconverted into light. The good thing is that they do not generate too much wilting radiant heat in IR as incandescent lamps do. </p><p>I think your arrangement with the aluminum foil in your recent 'ible will probably provide better heat removal if the LED strips are glued directly to the foil, with a cautionary note that you must ensure that the electrical connection points do not have foil beneath them to minimize the danger of short circuiting/ fire hazards.</p><p>Please keep updating your contribution as you watch the growth experiment progress!</p>
<p>Yes, i was meaning sink and not sync. Thanks for catching that.</p><p>Do you think that using foil instead of a cookie sheet would produce better heat dissipation? I chose to use a cookie sheet because it is rigid and it dissipates heat fairly well for the cost.</p>
What do you mean by a &quot;heat sync&quot;? I thought it was going to go into heating the soil to help germinate seeds, but then the &quot;sync&quot; was never referenced - save at the start.
<p>You could stack the trays to heat another one that is just germinating. Then shuffle them through as you go to plant. Just a thought.</p>
Whoops!! Ignore my comment. Sigh. *puts on dunce cap*
<p>how many watt is consumed in this setup? </p>
<p>72w is what they are rated to do, I have pulled close to 100w at the plug with no regulation (some inefficiency due to the power supply). This is why I have installed a voltage regulator to tame down the brightness and power consumption. I get very bright results from around 40w-50w. </p>
12V*6A=72W max. of power supply.

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