Lighting for Bonsai
The light visible to humans is 400 nm to 700 nm, a wavelength range called Photosynthetically Active Radiation (PAR) and much of the light that plants need is within this range. But will use other wavelengths for example, UV light (280 – 400 nm) is critical for optimal growth and far-red light (700-800 nm) is critical for flowering and fruiting. Known photoreceptors are most efficient in the blue and red area of the spectrum. Plants also reflect a significant part of light in the green area of the light spectrum, while absorbing a higher percentage of blue and red light as shown in the following illustration.
Creating a lighting environment for bonsai is not that difficult if given some thought, but it should be on a cost effective basis and easy to construct and maintain. There are various methods already in use including domestic (Household) lighting and that which is used in professional horticulture production.
Domestic lighting has gone through an enormous change since traditional incandescent bulbs were removed from the market and replaced with energy-saving bulbs. Three main types of regular light bulb are CFLs, (Compact fluorescent lamp) Halogen and LED. (Light emitting diode) All which have different values in their lighting properties for example. Watts and Lumens – the brightness of incandescent bulbs was measured in Watts, which is a measure of power for example, 40W, 60W and 75W. But measuring watts in energy saving bulbs is a less useful measure of brightness, because new bulbs use a lot less power to produce the same amount of light. Thus, their output is measured in Lumens and the higher the number of Lumens, the brighter the light.
Incandescent – (which still can be found) are usually clear or opaque having a tungsten filament inside. These bulbs emitted a warm yellowish glow and were common in domestic use, but to the consumer the cost ‘at-the-wall’, meaning the amount of power consumption was not considered cost effective. Moreover, their ability to provide enough light for plant growth was minimal at best, because they were unable to produce the light wavelengths that plants require.
CFLs – have a wide range of sizes and outputs and are considered to be four times more efficient than incandescent bulbs. The typical luminous efficacy of fluorescent lighting systems is 50–100 Lumens per watt, several times more than incandescent bulbs with comparable light output and are more cost effective. However, some CFL lighting can be expensive, because they require a ballast to regulate the current through the lamp, but lower energy cost offsets the higher initial cost.
As mentioned in the introduction various lighting set-ups were tested in a 2-year trial to test their efficiency in Bonsai cultivation. The image below shows a lighting fixture containing 2 x 13W – T5 CFLs producing 3000K delivering 980 Lumens.
This system showed that the angle and spread of light positioned (8cm above the leaf canopy) produced the best PAR. Although some of the smaller plants had to be elevated in order for the light to penetrate the lower leaf area. In short, this type of CFL lighting inexpensive ‘at-the-wall’ does work to some degree, but it is only white light not full spectrum, which is needed for strong growth. Nonetheless, CFL bulbs are now available in warm/red (2700 K), full spectrum or daylight (5000 K) and cool/blue (6500 K) versions. The usable life span of CFL compact or tubed ‘grow lights’ is approximately 10,000 hours producing 44-80 Lumens/watt, depending on the wattage of the bulb and manufacturer.
To find an alternative solution other lighting sources were investigated including Halogen, HID, (High Intensity Discharge) HPS, (High Pressure Sodium) and LED, (Light Emitting Diode) but the main priorities were and are (a) it had to be full spectrum and (b) cost effective. We now take a brief look at their capabilities.
Halogen – is similar to incandescent in colour and quality, as both use a tungsten filament and there’s little difference between the two in the amount of energy used depending on the bulb’s wattage. Halogen’s are significantly brighter, but like incandescent are unable to produce the blue and red wavelengths. In addition, halogen light is more expensive to run than other energy savers and with an expected life span of less than two years, a halogen bulb is unlikely to pay for itself before it needs replacing.
HID – lamps are able to out-perform all other lamps in their Lumen-per-watt efficiency and produce a color spectrum that is comparable to the sun. Such lighting systems including metal halide, high pressure sodium and conversion bulbs are available from an array of manufacturers in: 150W, 250W, 400W, 600W and 1000W. The most popular of this range and most electrically efficient as far as light produced are the 600W HID lights producing 7% more light on a watt-for-watt basis. However, all HID lamps work on the same principle, the different types of bulbs have different starting and voltage requirements, as well as different operating characteristics and physical shape. Because of this, a bulb will not work properly unless it’s using a matching ballast, even if the bulb will physically screw in. Mismatched bulbs and ballasts will stop working early, or may even burn out immediately.
HPS – lights are also used as a single source of light throughout the vegetative and reproductive stages and can be used as an amendment to full-spectrum lighting during the reproductive stage. They emit light in the yellow/red parts of the spectrum suitable for promoting flower and fruit. But if they are used for the vegetative phase as in Bonsai development meaning root, stem and leaf, the plants grow slightly more quickly, but will have longer internodes losing compactivity.
HPS lights have a long usable bulb life, and six times more light output per watt of energy consumed than a standard incandescent grow light due to their high efficiency. But, in the northern hemisphere during periods of the year where sunlight is scarce, metal halide lights are needed. To produce blue and violet wavelengths in balancing the light spectrum for proper growth.
LED – technology has been introduced into the grow light market by designing diodes to produce specific light wavelengths – the red and blue parts of the spectrum. NASA has tested LED grow lights for their high efficiency in growing food in space for extraterrestrial colonization. LED uses almost 90% less energy than other traditional grow light formats making them the most energy-efficient type of lighting. However, they are usually more expensive to buy, but can last up to 25 years depending on the manufacturer and in the long term they are the cheapest option available.
LED grow lights are usually composed of diodes incased on a ‘heat-sink’ with built-in fans. Which do not usually require a separate ballast and can be plugged directly into a standard electrical socket. The diodes used in early LED grow light designs were 1/3 watt to 1 watt in power however, higher wattage diodes such as 3 watt and 5 watt are now commonly used. Nonetheless, with any technology new to a particular market (Horticulture) one has to be aware of what is ‘good’ and what is ‘bad’. The reason for this consensus, is that not all individual LEDs or indeed LED light fixtures are reliable. Moreover, the claims made by some manufactures regarding PAR output and wattage, are exaggerated and some have included white LEDs in their lighting modules. Adding white LEDs in to a full spectrum lighting set-up serves no purpose, because plants do not use this wavelength.
Before considering purchasing a grow light for Bonsai, you should think of both current needs and those of the future. Time spent on research will help you find the correct lighting device, that is within your budget and also cost effective ‘at-the-wall’. Top rated LED Grow Lights are more expensive than HPS, HID or CFL systems and by understanding your limits you will be able to make the best decision.
Another factor to consider is the ‘size of the grow space’ – both the height and area (foot print) of your grow space is important. Whatever your choice of lighting system you will need a certain size light in order to cover the area. Many manufacturers provide a “core coverage” the amount of grow space that the light is capable of covering for example.
60cm x 60cm Grow Space = 1 x 180 watt to 240 watt lamp
60cm x 100cm Grow Space = 1 x 300 watt to 400 watt lamp
60cm x 150cm Grow Space = 2 x 180 watt to 240 watt lamps
150cm x 150cm Grow Space = 4 x 180 watt to 240 watt lamps (or equivalent)
150cm x 200cm Grow Space = 3 x 300 watt to 400 watt lamps (or equivalent)
These numbers give an approximation of how to scale up the grow area. With larger areas the lights must be placed correctly to ensure that maximum coverage is attained with no gaps as this will have an effect on plant growth.
The solution – considering the many options available and taking into account the grow area (90cm x 90cm) and cost effectiveness ‘at-the-wall’, the decision was to opt for LED. There are many LED ‘grow lights’ on the market from single bulbs to large fixtures. But for this research the choice was the Mars Hydro 3W series, a 132W true watt panel housing 48 LEDs with independent vegetation and flowering control. The unit was installed on the 27/01/2016 and in this short space of time plant growth has greatly improved. Further up dates on plant development will be posted. Bw – N.