High-power LED grow light – a build log

The product being tested on animals

The product being tested on animals

To make my growing season preparations more high tech I built a grow light with more than 25000 lumens light output while spending less than US$300. During the build I posted pictures/short notes on Makers, Hackers, Artists and Engineers Google+ community and received a lot of questions concerning LED choice, drivers, build of materials and construction details. This article is intended to answer these question and hopefully generate others – please don’t hesitate to ask!

The goal of this project was to produce a decent grow light for personal indoor gardening – mainly starting vegetables for subsequent transplanting outside some time in May and possibly extending the grow season in the autumn. While trying to determine necessary light output I realized that good numbers are impossible to find. By reading numerous indoor gardener’s forums I learned that people are having good results with light sources ranging from household-type compact fluorescent bulbs to high pressure sodium street lights. After analyzing pros and cons of all available light sources I decided to use high-power white LEDs. Here’s why:

  • They are low-voltage devices therefore they are much safer to work with than HID/fluorescent light sources. Low-voltage (<60V) LED drivers are also inexpensive
  • They are efficient as grow lights. Photosynthesis in plants occurs differently under different wavelengths of light; the “good” light is known as Photosynthetically active radiation (PAR). White LED emits most of its light in PAR – out of all light sources it produces most “PAR lumens” per unit of electricity used to produce these lumens. In addition, LED outputs all its light from one side therefore a light fixture doesn’t need a reflector.
  • They can last long time. LED manufacturers specify 50000 hours at some pretty high emitter temperature (75-85C) – it’s 11.4 years if lights are on 12 hours a day. At the end of 500000 hours a LED maintains 70% of its light output. The main factor here is temperature of the LED – if it is kept lower than specified the LED will last longer (and produce more light, see below).

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