Gavin Shoebridge – an electric vehicle nut, a keen environmentalist

                Electric Car Conversion Blog By Gavin Shoebridge

January 17th, 2016 at 11:38 am

Which is the better growing lamp: LED or CFL or sunlight?

LED growing lamp comparison with CFL growing lamp

LED (left) versus CFL (right) – click on this photo to see it full size.

In 2015 I bought a fancy 50 watt LED growing lamp (above left) from eBay which promised the earth in terms of spectrum awesomeness. I also went to the hardware store and bought a regular “warm white” 32 watt Compact Florescent Lamp (CFL) shown on the right. I wanted to know what was the best in terms of growing leafy vegetables but I didn’t know what was better.

Some websites said that the new LEDs are the way to go because they use them on the space station, others said that CFLs are better, but you need special “full spectrum” models which cost more. I was confused. The information on the internet is inconsistent. So, I did a little experiment…

CFL growing light comparison with LED grow lamp compared to sunlight

Chinese cabbages are fairly bulletproof so they’ll make good specimens. 

As you might remember from this blog post, I made a special growing box to carry out this experiment. I wanted to see if my fancy LED growing lamp was more effective than a standard CFL lamp from the hardware store, albeit brighter and more powerful than what most people would use to illuminate a room. Other than being 32 watts (a regular CFL is about 20 watts) it’s not special in any way.

Once I had the seeds germinating and sprouting (which took about 10 days before I started the experiment), I moved them into pots to begin the experiment. Don’t forget, you can click on any photo on this page to see it in full size.

CFL growing light comparison with LED grow lamp compared to sunlight

Day 1: LED on the left and CFL on the right.

I carried out this experiment because I wanted to see if I could grow vegetables during autumn and winter, which lamp was the most effective, and how both forms of light competed against the same vegetables using natural light in the glasshouse.

CFL growing light comparison with LED grow lamp compared to sunlight

I put two test cabbages in the glasshouse to compare growing with sunlight.

Because the growing season outside was effectively over, I put my two “sunlight cabbages” in the glasshouse to assist in their growth during these colder, shorter days.

CFL growing light comparison with LED grow lamp compared to sunlight

Day 7

Fast forward to day number seven. There’s very little difference between all three lots of cabbages growing inside and outside. It looks like the CFL might have an early advantage, but it’s only a guess. Let’s have a look how the outdoor cabbages compare on the seventh day:

CFL growing light comparison with LED grow lamp compared to sunlight

Day 7 outside: one cabbage died, the survivor fights on.

Oh dear. While the difference in size between indoor and outdoor cabbages might be negligible, the loss of the cabbage on the right is of concern. Were the cold temperatures just too much for it? Perhaps the roots were damaged during transplantation?

I didn’t know, but it was a bad start after just seven days. I watered and cared for them all as best as possible, and the next results were starting to show differences in progress.

CFL growing light comparison with LED grow lamp compared to sunlight

Day 14 in the growing box.

Day fourteen is starting to really show a difference in growth between the LED (left) and the CFL (right). This surprised me because the LED cost around $35 USD and had a glowing (pun intended) description of its growing abilities. The CFL on the other hand was just a regular lamp designed to illuminate your garage.

So how does my surviving outdoor cabbage compare after fourteen days?

CFL growing light comparison with LED grow lamp compared to sunlight

Day 14 outside.

The results are, perhaps predictably, rather gloomy in the glasshouse. While warmer during the day, at night the glasshouse temperature can fall to around freezing (0°C or 32°F) during late autumn / early winter. Still, at least that cabbage is surviving… just.

Let’s fast forward:

CFL growing light comparison with LED grow lamp compared to sunlight

Day 25 in the growing box.

Now things are starting to get interesting. The regular CFL lamp (right) is giving the cabbages all the right light to grow quickly and healthily, while the fancy LED (left) is making the cabbages grow in a rather scrawny way. Notice the colour difference, too?

These are impressive and surprising results. So how’s our little trooper going in the glasshouse?

CFL growing light comparison with LED grow lamp compared to sunlight

Day 25 with my hand for a size comparison.

Not only is the glasshouse cabbage surviving the now-winter conditions, it’s actually growing too, albeit very slowly. At this rate it’s obvious the glasshouse cabbage won’t win the race and it proves that even in a glasshouse, it’s not worth growing anything when the season’s over.

So let’s fast-forward to the final day in the experiment: day 36.

CFL growing light comparison with LED grow lamp compared to sunlight

Day 36.

The experiment has ended on day thirty six, which was the 6th of December. I took the indoor cabbages out of their respective sides in the growing box and had a good look at them. The LED cabbages did grow, and they grew well compared to the surviving glasshouse cabbage, but the final result was not how Chinese cabbages should look. Their leaves should be thick and dark, not pale and spindly.

The CFL cabbages on the other hand did remarkably well. I decided to brave the cold and put all the cabbages side by side outside so you can see the final result in one photo.

CFL growing light comparison with LED grow lamp compared to sunlight

We have a winner: CFL!

The results speak for themselves. In first place (left) are the two CFL cabbages, in second place are two rather sad looking LED cabbages, and in third place is one surviving glasshouse cabbage.

CFL growing light comparison with LED grow lamp compared to sunlight

The CFL cabbage grew so well that the pot was restricting its roots.

When I removed the cabbages from their pots I discovered something interesting. The cabbages which grew under the CFL light were fighting for space. At you can see above, the poor things had no space for their roots. I wonder what would have happened if I’d given them a bigger pot and given them more time?

CFL growing light comparison with LED grow lamp compared to sunlight

Getting to the root of the issue.

I rinsed the cabbages and their roots in water to remove the soil so I could see the progress of their root growth. Even though these cabbages were not yet fully mature, the winning CFL cabbages had strong root growth. Unfortunately the fine roots were weak and many broke upon removal.

The LED cabbages had other problems besides poor root growth. It was near impossible to move the LED cabbages because they were so weak. Any pressure at all resulted in broken stems and torn leaves. As for the glasshouse cabbage… well, that was too small to do anything with.

So how did they taste?

Well, very similarly. When eaten raw, the best tasting was the sunlight cabbage because it was lacking the usual “peppery” bitter cabbage taste. The LED cabbages were a little more bitter and cabbage-like, while the CFL cabbages were full-bodied with that tangy cabbage flavour.

I boiled what was not eaten and offered them around the house with a little soy sauce. Once boiled for 15 minutes they all tasted identical and all who tried them enjoyed them.

CFL growing light comparison with LED grow lamp compared to sunlight

If growing indoors during winter, forget LED and get a regular CFL instead!

And there you have it! No matter how good the advertisement may be for LED lighting, for leafy vegetables your best bet is a bright CFL from the hardware store.

Now I’m on to my next growing experiment: feijoas!

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