LED Test: Hot or Not?
In summer, heat can really dent your yield. Plants stretch...flowers set differently...growth is slow. And that's after you've dimmed or removed a light.
Imagine how much light and yield you're losing.
Sound familiar? What if you could beat the heat and keep your wattage high? Swapping to multiple LED lights could be the answer.
We decided to find out how they compare to CDM and HPS lights.
Overall, we found that:
- LED grow lights are 3oC - 4oC cooler per light
- LEDs increase your humidity to help cope with heat.
- Your temperature only increases by 1oC when you add an extra LED
The Aim
We decided to see what each of these lights did to the temperature, humidity & leaf temperature in a Large BudBox:
Just remember, if swapping a 600W light for a 240W LED or 315W CDM, your wattage drops dramatically...of course your temperature will be lower. So will your light output.
So, to be realistic, we also tested:
- 2 x 240W Telos 0008 (480W total - much closer to a 600W HPS)
What We Did
Normally, we run side by side tests. Not this time. To be as fair as possible, we decided to see how each light performed in the same tent, with the same plants.
Step 1
We kitted out a Large BudBox, with a:
- Brand new 5" RVK fan & filter
- 1 x 6" Clip-on Fan (4ft high at a 45o angle)
- 4 x lupin plants (flowering) in 12L RhizoPots
Our base readings were:
- Ambient air temperature was 20oC
- Airflow was 198m3/h
We tested each light, one after the other, in this tent.
Step 2
Before starting each test, we waited for the air temperature to return to 20oC.
For each light, we measured the:
- Air temperature
- Leaf temperature
- Relative humidity
We took two sets of readings for each light - 40 minutes and 80 minutes after lights went on.
Overall, 3 different temperature probes were used for accuracy. We also took the leaf temperature from the same leaf every time.
Results
As expected, LED lights were by far the coolest to run.
What did surprise us, is that adding a 2nd LED didn't really add much heat. Air temperature was still 3 - 4oC lower using 2 x LED's than it was using a single 600W HPS.
Based on these results, you could go to 3 x 240W LEDs (720W total!) and your tent would still be cooler than when running a 600W HPS.
As a bonus, the humidity was also higher when using LED lights! This helps plants retain water as they don't transpire as much.
CDM lights weren't too much warmer than LED lights - also a great shout in summer.
| 40 mins in | |||
|---|---|---|---|
| Air Temp | Leaf Surface Temp | Humidity | |
| 600W BAY6 HPS (magnetic ballast) | 25.5oC | 23.5oC | 39% RH |
| 315W Maxibright CDM | 23.9oC | 22.5oC | 42% RH |
| 240W Telos 0008 | 22oC | 19.5oC | 44% RH |
| 2 x 240W Telos 0008 | 22.6oC | 20.5oC | 43% RH |
| 1hr 20 mins in | |||
|---|---|---|---|
| Air Temp | Leaf Surface Temp | Humidity | |
| 600W BAY6 HPS (magnetic ballast) | 25.8oC | 24.5oC | 38% RH |
| 315W Maxibright Focus CDM | 23.9oC | 21.5% | 41% RH |
| 240W Telos 0008 | 21.9oC | 19.7oC | 42% RH |
| 2 x 240W Telos 0008 | 22.9oC | 20.7oC | 44% RH |
The Verdict
Really, it's a no brainer - if heat's a problem, swap to LED lights. Failing that, move to CDMs.
No more dimming or removing lights - by swapping in summer you can keep your wattage roughly the same (as long as you use enough lights).
Just make sure you've got a decent LED light - cheap ones that are badly made won't have the right light spectrum and may harm growth. Switching to them can do more harm than good.
Don't forget to switch back to your HPS lights in winter - you'll really need the extra heat then. You can still use any spare CDM lights to supplement your spectrum.
