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What is the best grow light for indoor plants?

 

Indoor growers have used a lot of different grow lighting technology over the years to grow plants indoors.

There are also a lot of variations of each grow light technology such as wattage and design to consider. Let's have a look at the main types of plant grow light available and the good and bad points of each.

Main types of grow light technology

  • Fluorescent grow lights
  • LED grow lights
  • HID grow lights (includes HPS and CMH technology)

Fluorescent grow lights are no longer viable

Fluorescent plant grow lights are now being phased out in most of the world due to their inefficiency and use of mercury. They are no longer sold in Europe and are scheduled to be removed from sale in the US in the next few years.

Fluorescent grow lights are no longer used and are being phased out in most markets

Fluorescent plant grow lights were rarely used for high intensity indoor growing and most commonly used to grow seedlings and young plants. Their shape was suitable for spreading low intensity light over a large area.

The fixtures are not cheap to buy or to run and can be replaced by far superior LED grow lights for low and high light intensity applications.

The exception is fluorescent UVB grow lights which are still most efficient way of delivering UVB to plants. It is a specialist use of fluorescents and is exempt from the fluorescent ban on general lighting applications.

UVB fluorescent grow light

LED grow lights

As with all types of lighting LEDs have become the most popular lighting technology used by indoor growers. In home and industrial applications LEDs have now replaced most older technologies due to their higher efficiency, lower running cost and flexibility.

There are two main components to an LED plant grow light, the LED driver and the LED light. The LED driver converts the alternating current (AC) power from your wall socket to direct current (DC) power the LEDs use.

The LED plant grow light can take many forms including light strips or bars, panels or small light bulbs in the form we are used to seeing at home.

LED bar grow light

LED grow lights are much more efficient

Plants need a lot of light to grow successfully. This requires a lot of electrical energy and energy prices have been going up. LED grow lights are at least twice as electrically efficient as HID grow lights and three times more efficient than fluorescent grow lights.

Grow light technology efficiency comparison LED HPS and Fluorescent

LED grow lights can be more expensive than HID grow lights to purchase up front. However you need higher wattage HID grow lights to match the LED grow lights. More significantly the lower running costs of LED plant grow lights pays back after 18 months and saves you money thereafter.

 

LED grow lights are much cheaper to run than HID grow lights

 

LED plant grow lights emit a better spectrum for plant growth

Plants require a grow light spectrum that is balanced, also known as 'full spectrum'. A full spectrum grow light outputs some blue, green and red light in the right proportion for healthy plant growth.

White LEDs deliver a full spectrum output and can be used to grow any type of plants at all stages of growth from a seedling to harvest of fruit and flowers.

LED spectrum is bets for healthy plant growth

Other benefits of LED plant grow lights

LED plant grow lights can be dimmed easily and efficiently to deliver precise light intensity levels. They can also be connected to external controllers so that multiple lights can be linked together and controlled simultaneously.

The heat output from LED plant grow lights is much less than fluorescent or HID grow lights. This means it is much easier to control the grow room temperature as there is less heat from LED grow lights to remove with extract fans or using air conditioning.

LED lights last much longer than fluorescent or HID grow lights and require no maintenance. Most LED grow lights will last 50,000 hours operation before there is significant reduction in light output. There is no need to replace bulbs frequently as is the case with HID and fluorescent bulbs.

Type of LED plant grow lights

 There are four main different LED plant grow light shapes and forms on the market:

  • LED bar grow lights
  • LED board grow lights
  • LED COB grow lights
  • LED grow light bulbs

LED bar grow lights

The most popular type of LED grow light is the LED bar type. This form of LED grow light spreads the light evenly across the grow area.

LED bar grow lights come in a large power range from 125 watts to 1,000 watts and different physical sizes to cover any grow area.

 MIGRO ARAY LED grow light

Because the light source is spread out there is less chance of a hot spot. Therefore the LED bar type fixture can be hung relatively low over the plant canopy. This increases the system efficiency of the grow light installation. The lower the light can be hung over the plant canopy the less light is lost to reflectance losses. Reflectance losses happen when light has to reflect off the side walls of the grow tent or grow room and does not reflect back onto the plant canopy.

Other benefits of LED bar grow lights is that the LEDs can be kept cool with each bar acting as a heatsink. It is easy for the heat to escape from the large total surface area of the LED bars. When LEDs run cool they last longer and run more efficiently.

There is lots of space between the bars for airflow to allow air to circulate around the grow room. This allows for good circulation in the grow room and access to the plant canopy.

LED panel or 'Quantum board' grow lights

This format is popular for smaller wattage grow lights up to about 200 watts. It is a very efficient type to produce which keeps costs down and allows mounting the LED driver to the top of the grow light.

LED board or quantum board grow light

The LED board type grow light can spread the light evenly over a small space reasonably well. Often grow light companies distribute the LEDs on the board more densely at the edges. This helps more even light spread and helps to prevent the high intensity 'hot spot' underneath and allowing lower hanging height for better system efficiency.

The downsides are that the LED driver can easily overheat when mounted on the back of the LED board heatsink. Also the board types do not allow for good airflow around the grow tent and visibility of the plant canopy.

LED COB grow lights

LED COB grow lights were popular in the early stages of LED plant grow lighting but are less common today.

'COB' stands for 'chip on board' and refers to the packaging of many individual LEDs on a small PCB board. Often they are grouped in circles which are yellow in colour.

COB LED grow lights

As the light source is highly concentrated the COB LED grow light has to be positioned higher over the plant canopy to prevent hot spots and spread the light evenly. For this reason they are less efficient at delivering light to the plant canopy than led bar lights. 

The high concentration of LEDs in a small space means it is hard to remove the heat effectively. Large heatsinks and sometimes fans are used to remove the heat which are heavy and expensive. This makes COB grow lights more expensive to produce than LED bar lights and is the primary reason they have been phased out.

LED grow light bulbs

LED plant grow light bulbs are very small led grow lights that can usually be fitted into a domestic lamp holder. They are low wattage and often used to light a single plant in a home setting.

LED grow light bulb

 

There is very little difference between a regular domestic LED bulb and a grow light bulb. They are both in the 10 watt to 30 watt range which will only emit enough light to grow a very small plant that extends no more than 8" x 8" or 20cm x 20cm in area.

The domestic bulbs often spread light in a wide arc that often will overshoot the plant canopy and be lost. The grow light bulb design will have an LED arrangement that directs the light down onto the plant more effectively than domestic bulbs. 

These bulbs are generally not used in larger growing operations and the large quantity of bulbs and the cabling and hangers to support them would make them impractical.

HID grow lights including HPS (high pressure sodium), MH (metal halide) and CMH (ceramic metal halide)

HID grow lights, HPS in particular, have been a reliable work horse for indoor growers for many years. They were much more efficient and higher power than any other technology before the availability of LEDs.

There are three main types of HID light available:

  • High Pressure Sodium
  • Metal Halide
  • Ceramic Metal Halide

HID grow light efficiency

They each perform differently in terms of efficiency of light output per watt. The HPS is the most efficient, CMH next and MH the least.

efficiency of HPS, MH and CM grow lights

HID plant grow light spectrum

The spectrum output is also different for each type of HID grow light. The main difference is the HPS has a small proportion of blue in the spectrum output compared to CMH and MH.
It is critical to have a minimum of about 5% blue light in the spectrum output. Plants are very responsive to the proportion of blue light. Plants grow short and dense when there is a lot of blue light and grow tall and 'stretchy' when there is not enough blue.
HPS CMH and MH spectrum output

When to use MH and HPS bulbs

Typically growers use MH bulbs in the early 'vegetative' stage of growth. In this stage plants do not require very high light intensity. However the high proportion of blue in the MH spectrum  is useful for growers to keep the plants small and compact. 
Growers then switch to HPS bulbs for the flowering cycle when plants benefit from the more efficient and higher output HPS bulbs to grow more vigorously and maximise the harvest weight.

When to use CMH bulbs

CMH bulbs are both high efficiency and have a spectrum that can be used for all stages of growth. However they are more expensive than wither MH or HPS bulbs and require dedicated and more expensive ballasts.

HID grow light equipment over view

The three main components in a HID grow light are the ballast, the bulb and the reflector.

Typical HID grow light equipment

Inside the protective glass tube are HID light bulbs filled with gas and other particles. When an electrical current is passed through the gases they emit light. Different gases and particles emit different light wavelengths or colours.

The gas is initially ignited by a high voltage spark across the inner tube. The Ballast is a power supply and controller combined and is needed to generate the starting voltage spike and control the current and voltage to the bulb. Metal Halide and High Pressure Sodium bulbs of the same power ratings can be run on the same ballast.

The reflector directs the light down onto the plant canopy. There are a wide range of HID reflectors available on the market. In general the larger reflectors are more efficient and deliver light more evenly to the plant canopy.

Heat output from HID grow lights

As HID grow lights are less efficient they emit a lot more heat into the grow room. This can be a problem for indoor growers as the heat has to be removed so the room temperature is kept at an optimum to keep the plants healthy.

This can mean there is a lot of extra equipment and energy required to manage the environment.

What is the best type of plant grow light?

LED bar type plant grow lights are the most common available on the market for a reason. As an LED plant grow light they are more efficient and provide the best spectrum for growing all types of plants at any stage of their lifecycle.

In addition LED bar grow lights produce the most even light spread. Being able to position the lights closer to the plants means they operate more efficiently than other grow lights due to lower light losses to overspill or reflectance losses.

The added benefit of cheaper construction and better cooling result in the best value for money LED plant grow light with the longest lifespan.

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