Switch from HPS to LED Lighting

Your Guide From HID to LED Grow Lights


We have talked before about the benefits of LED lighting over HIDs, and in recent years  we have seen more and more growers make the switch from HID to LEDs. Converting to LEDs can be one of the best things you can do for your plants and for your wallet. You will save money on energy bills and be able to have more significant control over your final yield.

However, the conversion process can be a little tricky – especially if you already have a carefully laid out physical setup in place.

LED and HID lighting conversion is a complex process. The truth is, there is no one-size-fits all answer, so giving blanket advice can be tricky. Flexibility is ultimately key to success as a lot depends on the specific strains you are growing as well as the logistics of your operation. What may work for one individual may not necessarily be the best route for another, but there are some general guidelines to be aware of when switching to LEDs.

Finding The Right LEDs

If you have a grow setup already in place, you cannot simply swap out your HID lights for LED fixtures without making sure you are getting a similar PAR output. This ensures your plants get the same amount of nutrients under your new lights as they did under your original setup.

LED light fixtures should all list their rough PPFD range, which gives a rough measurement of the amount of PAR that actually reaches your canopy. You need to purchase a fixture with a PPFD range similar to your current setup.

If you do not already have a light meter, purchase one – which you can do online or at a local garden supply store. Turn on your HID lights on and give them enough time to warm up. Then, hold your probe’s meter in the center of your growing area, making sure the light is the same distance from your meter as it is from your plants. The meter should then display your PPFD.

However, it is not always as simple as picking an LED fixture within this range. For an LED fixture, the precise distance a light is from your plants affects PPFD levels. Given the capacity of your space, determine what is reasonable in terms of the distance from the canopy to your lights.

For example, say your plants currently receive 500 PPFD and you are choosing between two different LED fixtures. The first fixture can get 500 PPFD at 24-inches, but the second gives 500 PPFD at 30-inches. If you have a smaller space, and 24-inches is the highest you can go.

Therefore, you are better off choosing the first fixture.

Factoring In Temperature

One of the biggest benefits of LED lighting is that temperature regulation is far easier. HID lights not only generate significantly more heat, but they generate heat faster. As a result, your ambient room temperature can safely be about 10 degrees higher when using LED lights.

HID lights only convert a small fraction of the energy they use into visible light and the rest is released as infrared energy, which heats surfaces directly. When plants are grown under HID bulbs, they receive a significant amount of infrared light. Therefore, their surface temperature can be significantly higher than the temperature of a room.

LED lights produce little to no infrared energy. They instead release excess heat into the air, which can easily be removed with circulating fans and air conditioners. The surface of plants grown under LED lights may only be two to three degrees warmer than the room.

Leaf surface temperatures are of course very important for plant growth, as this is where photosynthesis reactions occur. As previously mentioned, the best conditions for your plants are highly dependent on a number of individual factors, but speaking broadly most growers find that:

  • Under HID lights, plants grow best at a room temperature between 70 and 75 degrees Fahrenheit
  • Under LED lights, plants grow best at a room temperature between 80 and 85 degrees Fahrenheit

If you are making the switch to LEDs, try starting with a room temperature in the lower 80s and adjust as needed (some find 84 degrees is a good starting point).

Accounting For Stretching

Switching to LED lighting will have a major effect on how your plants grow, which can lead to a more robust yield in many cases. However, any changes – even positive ones – require some adjustment to your grow space.

In nature, plants stretch when they sense they’re being shaded by taller plants. They do so by measuring the ratio of the far-red light versus visible light they receive. Plants exposed to more far-red light tend to stretch out, growing longer leaves and stems.

Higher levels of other spectrums – blue light especially – can result in shorter and stockier plants. With LED lighting, you often have far more control over your color spectrum, and can adjust settings throughout the grow cycle to tailor plant growth, which can either prevent or encourage stretching.

When making the switch to LED lighting, take into account how your plant sizes may change under different conditions and whether or not you need to adjust your layout.


One of the major benefits to LED grow lights is that they are vastly more electrically efficient than HID lights. This means your room can operate at a warmer ambient temperature, which means air conditioners – when set to maintain a specific temperature – will run less often. While this saves you a lot on electricity, it can affect the general humidity of your room.

When using HID lights, ACs often naturally dehumidify, meaning that many growers do not have to invest in additional equipment. Some growers may need to purchase a dehumidifier after making the switch to LEDs.

If you do not already have a hygrometer, we recommend investing in one before converting and keeping a close eye on humidity levels.

HID to LED Grow Lights: The Bottom Line

There is no one-size-fits all solution when it comes to converting to LEDs. In fact, talking to a grow specialist may be necessary if you’re running a large scale operation. Factors like temperature, PPFD levels, humidity, and changes in plant height and width all come into play when adjusting your setup.

Sometimes, the changes you need to make are not entirely predictable, so be prepared to be flexible during your first grow cycle using LED lights. While the transition may have some rocky moments, in the long run you’ll save money and get higher quality yields.


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