Why LED Lights? – LED vs HID

In the past few years, LED grow light technology has evolved immensely and gained great popularity. However, there is still a raging debate in the community about whether these lights can outperform the good old HIDs. While LEDs work quite well in most growing circumstances, HIDs too can be a good choice in some situations. Let us take a closer look at how each technology works, and which one is best for you.

HID Grow Lights

High Density Discharge Lights (HID) are known for the intensity and brightness of the light they emit. The light is intense enough to penetrate the canopy and reach the entire plant to nourish it.

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How do HID lights work?

HID uses centuries-old technology wherein light is produced by passing electric current between two tungsten electrodes placed inside a glass tube containing metal salts and gases. With sufficient current, the gas acts as a conductor and creates an arc between the two electrodes. The intense heat generated by the arc causes the metal salts to vapourize, which intensifies the light generated by the arc stream. You get different quality of light with different mixtures of metal salts.

There are two types of HID bulbs used in grow lights-High Pressure Sodium (HPS) and Metal Halide (MH).

Metal halide bulbs generate a cool, blue spectrum that is suitable for the vegetation stage of plant growth. On the other hand, high pressure sodium bulbs produce orange to red spectrum that appears gold or yellow to human eye. These bulbs are perfect for flowering stage.

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What are the key components of HID grow lights?

The grow light needs a reflector hood that directs the light. Some grow lights have MH or HPS bulbs only, while some allow switching as well.

The reflector hood also includes a cooling mechanism, because the HID bulbs tend to become hot. However, this cooling is usually not enough and it needs additional cooling as well.

The light needs a ballast to power it. It converts the mains power into power that the HID bulbs can use. The bulbs are also of two types: digital and magnetic. So, you need ballast that matches the type of bulb and its wattage. The best ballasts are the ones that are digital, dimmable and versatile.

You can easily find an HID light that has all of these.

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Pros: HID grow lights

  • Tried and tested technology, there is ample information available, which makes it easy to use the lights effectively. These lights have been used for over thirty years by hydroponics enthusiasts and indoor growers. They have a proven record of improving plant growth and yield.
  • Intense and bright light that penetrates the canopy to reach the entire plant and nourish it
  • Low initial cost, which is helpful if you need many lights at one go. It also makes replacement less expensive
  • HID lights are often dimmable, which makes it easier to customize light for a particular area
  • MH bulb spectrum includes ultraviolet light, which is helpful in last stages of flowering. HPS bulbs are suitable for the entire plant growth cycle, however, the for veg stage MH bulbs would work better.

Pro tip 1: It is a good idea to combine HPS and LED grow lights for larger grow spaces. While the HPS grow lights can provide deeper penetration, LED grow lights at the periphery can give fuller spectrum and provide complete coverage.

Pro tip 2: For a large commercial grow space, 1000W HID is a good choice, for domestic use anything under 600W would work well.

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Cons: HID grow lights

  • Higher long term operating costs, because the bulbs need frequent replacements. HID bulbs may degrade up to 15 percent after a year of use becoming less efficient and bright. Normal lifespan of HPS is up to 18,000 hours and MH is 10,000 hours. Most professional growers replace their HID bulbs at least once a year and some even replace them after every 2 harvests. This translates into significant ongoing costs.
  • HPS bulbs generate a lot of heat. They need to be hung higher compared to other lights. So, they cannot be used in grow spaces with lower roofs. Also, they can pose a potential fire hazard if not cooled properly. This makes then unsuitable for use in confined spaces.  It also causes more evaporation, so you need to spend more on water and utility bills.
  • These grow lights are not too efficient, because they rely on reflectors to direct the light. This causes up to 15 percent efficiency loss.
  • HPS bulbs create more yellow and green light than required by plants leading to energy wastage
  • They require additional hardware to operate such as a reflector and ballast. Some ballasts will only operate HPS and some will only operate MH, which means, you may need multiple ballasts.
  • HID’s fixed spectrum output is not ideal for plants. In fact, most of the HPS spectrum actually falls in the region of lowest plant absorption (as shown in the graph below).
  • HID bulbs contain toxic metals that are not environment friendly
  • HID lights under 400W are quite inefficient and those above 1000W are suitable only for large commercial grow spaces.

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Difference between HID and LED lights

Unlike HID lights, LED lights do not use any kind of bulbs. Instead, they use LED chips or diodes that turn electricity into light, directly and efficiently.

Inside each LED bulb there is a semiconductor material consisting of positively and negatively charged components. When you turn on the light and electricity strikes the semiconductor, the electrons become charged and start flowing from a negative to a positive layer within the semiconductor. When these excited electrons pass through holes in the material, they emit photons of light causing the LED to illuminate.

Just like HID, some colors of LED are more energy efficient than others, but LED lights still use much less wattage compared to an equivalent HID. LED grow lights can help reduce energy consumption buy up to 70 percent. Moreover, you don’t need too much peripheral hardware such as ballasts and hoods.

LED grow lights are very convenient to install and use. You can easily raise or lower the height of these lights for different grow stages. What more, many LED grow lights come with two different modes for switching the spectrum based on the plants’ growth stage. There are more advanced versions of LED grow lights available that come equipped with Wi-Fi, remote control, touch screens or auto programs.

Another key difference is that LED lights generate very less heat compared to HID grow lights. So, there is much less energy wasted generating heat. Also, it takes up to 50 percent less energy to cool them. The best thing is that most LED grow lights are designed in a way that whatever heat is generated is directed upwards, away from the plants. This prevents potential heat damage to the plants.

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Pros: LED Grow Lights

  • A full spectrum LED grow light can be used for a full grow cycle. In fact, in many LED grow lights you can switch between two modes to select the right spectrum for the particular grow stage
  • Even the most powerful LED grow lights are more efficient than HID lights
  • LED grow lights can deliver a precise spectrum, which means, there is no electricity wasted to produce light that is of no use to your plants
  • They don’t create much heat, so you can place them closer to plants.
  • These grow lights provide a high yield per watt.
  • Most LEDs have a lifespan of over 50,000 hours. They remain efficient throughout their lifetime.
  • The lights produce less heat so plants require less water.
  • These are much easier to maintain compared to HID lights
  • LED grow lights come as all-in-one fixtures, and are easier to work with in tight spaces
  • Lower operating costs and utility bills

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Cons: LED Grow Lights

  • LED grow lights have a higher upfront cost. Compared to an HID light, quality LED grow lights may cost from 2-5 times as much per square foot of light coverage. However, the power draw is lower and there are no parts to replace so they prove cheaper than HID lights in the long term.
  • LED grow lights produce less heat, which is beneficial in most situations and helps you save money on air conditioning. However, in colder indoor areas you may need to supplement with extra heat using an HID light.
  • There is a common misconception that LED grow lights can be kept as close to the plants as you want, because there is less heat. Although this is true, the light from a modern LED is much more intense and will cause light burn (bleach) from excess light regardless of the leaf temperature. It’s best practice to keep powerful LED grow lights at least 1 foot and in many cases 2 foot from your plants in order to avoid light burn.
  • Inconsistency across different models from different manufacturers. Each LED grow light model uses a unique blend of diode sizes, colors, lenses, and more. Due of this, you may have to use two similar models differently to get the best results.
  • Manufacturers often make confusing claims about specs making it difficult to compare models and make the right choice. This usually relates to the LED wattage claims and its actual current draw

Pro tip 3: A good rule of thumb is to aim for 35watts per square foot by dividing actual current draw with your grow space area.
Pro tip 4: Two LED’s that draw 250 watts each for a total of 500 watts will provide much better results than a 600 watt hps.

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Over the years, LED grow lights have evolved and reached a point where they can replace even the best HID lights in almost every situation. This does not mean that HID lights are ineffective. They are still a good choice especially if you don’t want to spend too much upfront.

If you are looking for lower operating costs and maintenance, better efficiency, higher lifespan, reliability and convenience, LED grow lights are the perfect choice.

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