Firefly Growlight

Growing Cannabis with LED

Growing Cannabis with LED

Growing Cannabis with LED

Changing from HPS to LED → Why

There are a bunch of reasons that growers consider when changing from HPS to LED growlights. Not all may be equally applicable to everyone’s situation, but it’s a good start to list the most important ones:

Power saving

Although it’s true that, since LED’s have become so much better in the last few years, it is now possible to switch a 1000W HPS Growlight fixture for a lower energy consuming LED fixture. Depending on the quality of the fixture, this change can lower the energy consumption from 1000W to 720W or even 600W while getting roughly the same amount of light.

However, when we were building the first jet-engine powered jets, did we want to save energy, or did we want to go faster? The same argument can be made with growlights: you can either save energy with the same amount of light, or just boost the light you are getting by using the same amount of power.



Heat management

This subtitle should probably be “climate management”, since heat and humidity and airflow are strongly interrelated. By changing your 1000W HPS Growlight to a 700W LED Growlight, you will bring less external heat into the growroom. That’s true most of the time. However, now you must also change your airflow to keep the same plant/room temperature. Then there is the nutrient and

irrigation program that needs to be adapted to less evaporation from the soil. And finally, less evaporation in the room will also likely drop the humidity in the room. Keep an eye on all these factors with sensors if possible and adjust constantly to get it right!



Light quality

With your good old HPS growlight, your plants used to grow just fine. Now with the new top-shelf LED growlights, they stay shorter and might not yield as much as with your old lights. What the hell happened? Well, you’ve basically improved the quality of your light output. With HPS lights, the focus was mainly on getting as much Red and Far-red on your canopy as possible. Red and farred are very efficient energy transfers for

photosynthesis and will stimulate cell-division and hence will bring you larger plants. Adding more blue to the mix, as with most modern LED’s, will actually balance the cell-division to more optimal balance (optimum for cannabis is around 10-20% blue light) which will keep your plants more compact. Now, really good LED growlights will even add a lot of Green, Yellow and even UV into the mix. Green will actually keep lower leaves producing healthier amounts of energy for your plants and UV will increase CBD/THC and terpenes production in your cannabis plants. Our advice to deal with smaller plants and lower yield per plant: put more plants in your growroom!

Durability and maintenance

HPS bulbs generally need replacement after about 1/1.5 years or 10,000hrs in order to keep efficiency at max. This is usually a good time to dust of the reflectors and other parts of the light. With LED’s, which will run for at least 50,000hrs (even up to 80,000hrs are guaranteed with some lights), this cleaning and maintenance cycle is not there anymore. So, should you clean them? Yes. All you need is a damp cloth and just wipe them down –

particularly the lenses and covers. Easy and better.

So if you found any arguments above here to switch from HPS to LED, here comes the difficult part: how to switch? Except from the obvious: “take one light down and hang the other one up”, there is more to it.


Less watering?

Less watering can mean less frequent watering or giving less water, so which one is it? With your HPS lights, the heat from above was a lot more and probably your HPS bulb emitted some Infrared rays as well. This heat and radiation heat would dry up the top of your pots a lot quicker than LED growlights will. This is caused by evaporation which in turn caused higher relative humidity in your room. So, say that with your old HPS growroom, you had the perfect balance of heat, humidity and airflow in your room. You might have even added some CO2 in the room. Now you must completely re-balance these 4 factors in order to get to the same optimum again. Our suggestion would be to start reading up about VPD (Vapor Pressure Deficit) which will help you find the ideal levels in your room before changing the lights. And as a general rule of thumb: with LED’s you may give less water per turn, however you may increase the frequency. If you give less water per turn, you can increase the EC in your tank if needed.

How many lights?

Not only is the technology of LED’s different from HPS growlights, also the way they look is much different. The HPS lights need a reflector to 1) catch the light going up as well and 2) produce an even spread on the surface below. Most LED’s nowadays look like futuristic clothes dry-racks. So, the shape of the light has a big influence on how to use it. Surely, you can’t cram a 1.6×1.2m Spider with a 1000W in 1x1m growbox (this used to be possible with a 600W HPS fixture). Secondly, your old HPS bulb might produce so much heat that you couldn’t really hang it close to the canopy or it would cause heat-stress. With LED’s this is again possible. Also, the spread of light on the canopy allows for much closer growing then before. In vertical farms the lights are as close as 30cm’s from the canopy. So, the question is how many lights do you need now vs how many lights did you have before? It depends on the height of your room and whether you were using a controller or dimmer. You generally want to be able to vary between 300 μmol/m2/s for propagation and start of veg to 1000 μmol/m2/s (or even up to 1500 μmol/m2/s if you are using CO2) in flowering phase. Do you need to cover every little square cm of the floor with as much light as possible? No, you can also move your plants around. If you have so many plants that the last advice is too much work, keep in mind that you need space around the plants to work as well. Don’t just change the same amount of HPS for the same amount of LED’s; you may need less of them then you think.