T5 Fluorescent Grow Light Vs. Low Watt LEDs In Lettuce Test

lettuce test of grow lightsLEDs are clearly better than fluorescent grow lights, right?

Well, not always. It really depends on the LED in question.  And for small grows, I’ve always said you’re better off just using a fluorescent light.

This experiment proves that. It also shows the ineffectiveness of using all-blue light for vegging. Sure, plants need more blue light during vegging than flowering, but they still need the other colors, too. The ideal vegging light has more blue light, but not only blue light.


The Experiment

This guy grew a head of lettuce (he used seedlings first, but discarded that experiment) under three different lights. One light was a T5 fluorescent grow light, the other a 15 watt all-blue LED (for vegging) and the third a 45 watt red and blue LED.

He actually tried a different fixture at first, but it didn’t draw the claimed wattage. Neither did the second, but he went with 45 watts to ensure it was powerful enough even if it didn’t deliver as advertised. This just shows you how many bad manufacturers are selling low-cost LEDs on Amazon. You really have to be careful.

In terms of cost, all option were fairly close when calculated on a cost per square inch basis, though the LEDs would cost less to run long-term. How about the results? See for yourself.



The T5 used about 48 watts per plant and resulted in the most growth by far.

The 45 watt red and blue LED used about 29 watts and did well, but not as well as the fluorescent fixture.

The 15 watt blue LED did virtually nothing. Even in his original experiment with the seedlings, this light proved to be basically useless. Everyone always says that plants need blue light when vegging, but they don’t ONLY need blue light. They still want other colors as well, especially red. They just consume more blue light during vegging than during flowering.



These results verify what I’ve always said. Don’t bother with these low wattage LED fixtures, unless you’re using them as supplemental lighting. And in this case, they were only being asked to veg. If you tried to use them to flower a plant, the results would be even more dismal (you would also have to hang them at a lower height).

If you want to replace a fluorescent fixture with LED light, you need to get an LED fixture that draws at least 30 watts per square foot. Anything less just won’t cut it on its own. Ideally, you want to get something even more powerful than that, if you are really trying to take advantage of the cost and heat savings that LED lights can provide over fluorescent grow lights and HID lighting systems.

But really, for small gardens like the one in the video, you’re often best off using a fluorescent light, unless you can afford to spend a few hundred dollars on a quality LED fixture. If you’re not sure which type of fluorescent lights to get, check out this post.


August 10, 2017

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