3 Watt vs 5 Watt Diodes for LED Grow Lights

In a quest to find the best LED grow lights, I came across the question of which is better, 1w vs. 3w vs 5w diodes. I first started researching the history of LED grow lights and then compared different models of lights with varying diode sizes. My research led me to the following analysis.

LED grow lights have come a long way since the 13 watt panels consisting of 225 diodes each drawing one eight to one sixteenth of a watt of power. Those 15 row by 15 column panels were not able to grow much of anything except simple grasses and sprouts, and did not even do that very well. Those initial cheap panels gave LED grow lights a bad name for years until stronger diodes became readily available.  I am surprised that these 225 diode models are still being sold today.

Shortly thereafter, LED grow light manufacturers starting using 1 & 2 watt diodes in LED growlights. The larger wattage diodes provided a great improvement over the smaller diodes. They were able to penetrate a plant’s canopy three to four feet. Although this amount of penetration sufficed for most growers, the commercial growing segment of the indoor growing market needed a plant grow light that could reach down an extra foot or two to the bottom of the plants.

In 2009, many LED grow light manufacturers starting using 3 watt diodes in their grow lights. The 3 watt diode provided the ideal balance of canopy penetration without being plagued with heat issues that come with larger diodes. With 3 watt diodes, a grow light was able to penetrate up to 5 feet past the plant’s canopy and was the perfect design being demanded by the indoor growing market.

Shortly after 3 watt diode light were introduced, clever marketers started manufacturing indoor grow lights with 5 watt, 10 watt and even larger diodes. On the surface this seems to be natural progression for grow light strength, but the LED grow lights with the larger diodes have some very critical drawbacks. The first issue is that of heat dissipation and density. As the diode size increases, so does the amount of heat that needs to be dissipated by the diode chip. Larger wattage diodes need larger heat sinks to dissipate the heat that they give off. This results in heavier and bulkier lights. Another critical design drawback of the larger diodes is that they can not be packed as densely as the 3 watt designed lights. When using 5 watt or 10 watt diodes, you must space the diodes further apart, again because of the problem of heat dissipation. The result is a less densely packed grow light that is heavier and bulkier.

The biggest drawback of the 5+ watt diodes is their price. Not only do they cost more overall, but they are also more expensive on a $/watt and $/ growing area covered basis.  A quick analysis shows that it is not worth paying a premium to have larger diodes in LED grow lights. The added penetration is superfluous and unnecessary for indoor growers and it comes at a burdensome cost – increased price and less densely packed network of diodes.

Bigger is not always better. When it comes to the question of 3 watt  vs 5 watt diodes for LED grow lights, the 3 watt diode is the smarter choice for any indoor growing project.

Ehud Muhlev, PhD. EE

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