Horticultural lighting systems allow you to extend the growing season by providing your plants with an indoor equivalent to sunlight. This is a great advantage for those of you who appreciate having a year-round supply of fresh flowers, veggies and herbs. Artificial lighting is also a great way to jump-start spring by starting your seedlings months ahead of the last frost. There are three main types of horticultural lighting systems.

Lighting is one of the five major factors to consider when creating a support system for your plant life, (water, nutrients, oxygen and CO2 are the others).  Thus if you plan to grow inside, out of season, you must supplement the sunlight normally required for proper growth.  This can be done with three different kinds of lighting, incandescent, fluorescent, and H.I.D. (High Intensity Discharge).  These are the most popular types of lighting for gardening purposes.  There are many other kinds of lighting, but they don't produce proper color (kelvins) that is suitable for growing.

Incandescent lighting

These are the least efficient and least effective method of lighting, for plant growth.  Incandescent lighting is the same as what is used in the average medium base household fixtures.  This type of lighting is a very poor choice of lighting for your garden because of their inefficiency.

Fluorescent lights

These are a little better choice than incandescent lights due to the fact that they are about twice as efficient (lumens of light output per watt of electricity used). However these lights are not very effective in comparison to an HID (High Intensity Discharge) system and these lights must be less than 12 inches away from their subjects to ensure successful growth.  However, some find that our T-5 fluorescent lights are perfect for use with seedlings and cuttings as well as for use with other plants that do not require the high intensity of H.I.D. (High Intensity Discharge) lighting.

H.I.D. (High Intensity Discharge)

These lights are by far the most efficient and effective lights being used by growers today.  There are two types of H.I.D. (High Intensity Discharge) lamps that have suitable light spectrums (color range) and intensity for plant growth.  MH (Metal Halide) lamps are rich in the blue light spectrum, similar to full summer sun.  HPS (High Pressure Sodium) lamps are rich in the red/yellow spectrums, similar to the color of the fall sun. 

HID (High Intensity Discharge) Plant Grow Lights

Metal Halide - MH

MH (Metal Halide) bulbs are very efficient and produce between 70 and 115 lumens of light output per watt of electricity used. MH (Metal Halide) bulbs produce a light that is very close to full summer sun, with a spectrum rich in the blue end. This promotes fast vegetative growth and compact, stocky plants with short internodal leaf spacing. 

Metal halide bulbs produce an abundance of light in the blue spectrum. This color of light promotes plant growth and is excellent for green leafy growth and keeping plants compact. It is the best type of light to be used as a primary light source (if no or little natural sunlight is available). The average lifespan is about 10,000 cumulative hours. The bulb will light up beyond this time but due to the gradual decline of light, it is not worth your while to wait for the bulb to finally burn out. If you compare their lumen (brightness) per unit of energy consumed, metal halides produce up to 125 lumens per watt compared to 39 lumens per watt with standard fluorescent lights and 18 lumens per watt for standard incandescent bulbs

MH (Metal Halide) bulbs create light by passing electricity through an clear inner arc tube that is enclosed in the vacuum of an outer clear glass tube.  This inner arc tube contains mercury and other metals in iodide form.  When electricity is applied to these metal iodides they give off very intense light and heat.  The outer casing can also be phosphorus coated.  Most gardeners prefer the clear bulb, as it produces the brightest white light available.

MH (Metal Halide) bulbs come in sizes from 70 to 1500 watts with the 250 w, 400 w and the 1000 w being the most popular sizes for gardening. All MH (Metal Halide) bulbs need to run with a ballast (a ballast is a transformer that steps up the voltage to the proper amount needed to ignite the iodides), that is designed to run that specific bulb size.

The bulbs themselves need to be burned in a specific position. They come in three types: Vertical (marked BU or BD), Horizontal (marked HOR) and Universal (marked U). The universal bulbs can be burned in any position, but they still are more efficient when burned vertically.

MH (Medal Halide) bulbs should be replaced about every 10,000 hours of use or approximately 18 months (as per an 18 hour / day on cycle).

High Pressure Sodium - HPS

High pressure sodium bulbs emit an orange-red glow. This band of light triggers hormones in plants to increase flowering/budding in plants. They are the best grow lights available for secondary or supplemental lighting (used in conjunction with natural sunlight). This is ideal for greenhouse growing applications.

Not only is this a great flowering light, it has two features that make it a more economical choice. Their average lifespan is twice that of metal halides, but after 18,000 hours of use, they will start to draw more electricity than their rated watts while gradually producing less light. HPS bulbs are very efficient. They produce up to 140 lumens per watt. Their disadvantage is they are deficient in the blue spectrum. If a gardener were to start a young plant under a HPS bulb, she/he would see impressive vertical growth. In fact, probably too impressive. Most plants would grow up thin and lanky and in no time you will have to prune your plant back before it grows into the light fixture. The exception to this is using HPS grow lights in a greenhouse or in conjunction another light source that emits light in the blue spectrum. Light sources that have a high output in the blue spectrum like sunlight and MH grow lights offset any stretching caused by HPS bulbs.

HPS (High Pressure Sodium) bulbs are the most efficient bulbs that are available for grow lights.  They are high in the red and yellow parts of the light spectrum and low in the blue, this imitates the fall sun.  Because of this spectrum some plants that are grown with HPS (High Pressure Sodium) lights will grow elongated and rather leggy, while many other plants are not affected by the limited light spectrum.  For plants that normally bud and flower in the fall an HPS (High Pressure Sodium) is usually the light of choice because it's light spectrum promotes flower production.

There are color corrected HPS (High Pressure Sodium) bulbs (such as the Son Agro) available for improved growing with HPS (High Pressure Sodium) efficiency.  These are designed specifically for indoor horticulture, and have a more balanced color spectrum.

HPS (High Pressure Sodium) bulbs are made out of a translucent ceramic arc tube containing a mixture of sodium, mercury and xenon gas. This arc tube is suspended in an outer glass shield (bulb). HPS (High Pressure Sodium) bulbs range in power from 35w to 1000w, with the 250w, 400w, 600w and 1000w being the most popular for horticulture use.

HPS (High Pressure Sodium) bulbs should be changed no later than 24 months from initial use. These bulbs (like the Metal Halides) also slowly lose their brightness over time, so to maintain proper light intensity the bulbs must be changed at the end of their rated life.

HID (High Intensity Discharge) Plant Grow Lights

HID lighting is the most efficient way to convert electricity into light that is available to the consumer. There are two types of HID grow lights used for horticultural lighting:

HID Light Output	Primary Growing Area	Supplemental Growing Area
100 watts	2' x 2'	3' x 3'
250 watts	3' x 3'	5' x 5'
400 watts	5' x 5'	8' x 8'
600 watts	6' x 6'	10' x 10'
1000 watts	8' x 8'	12' x 12'

HID Lighting Helpful Tips

.Hanging height:

Due to the heat that is emitted from these types of fixtures, you should hang them according to size. Smaller wattage systems (100 and 250) should be hung about 2 to 3 feet from the top of the plants. Medium wattage systems (400 and 600) should be hung around 4 feet from the top of the plants. High wattage systems (1000 and up) should be placed at least 4 to 6 feet from the plant tops.

.How long should lights run?

This depends on the type of plant. Most plants and vegetables need about 10 to 12 hours of light to promote growth. Plants that produce fruits or flowers will show improvement with up to 16 hours a day of supplemental light.

Selecting a Grow Light

Plants have the unique ability to manufacture their own food. The food manufacturing process is called photosynthesis.  Photosynthesis is carried out by many different organisms, ranging from plants to bacteria. The best known form of photosynthesis is the one carried out by higher plants and algae, as well as by cyanobacteria and their relatives, which are responsible for a major part of photosynthesis in oceans. All these organisms convert CO₂ (carbon dioxide) to organic material by reducing this gas to carbohydrates in a rather complex set of reactions. Electrons for this reduction reaction ultimately come from water, which is then converted to oxygen and protons. Energy for this process is provided by light, which is absorbed by pigments (primarily chlorophylls and carotenoids). Chlorophylls absorb blue and red light and carotenoids absorb blue-green light, but green and yellow light are not effectively absorbed by photosynthetic pigments in plants; therefore, light of these colors is either reflected by leaves or passes through the leaves. This is why plants are green.

Cool (blue) and warm (orange) colors in the spectrum enhance chlorophyll activity and food production. Cool light is most pronounced during the summer months when the sun is highest in the sky. It is responsible for keeping plants growth compact and shapely. Warm light, such as when the sun is lower in the sky during the fall harvest months, is responsible for triggering reproduction in plants in the form of flowers and fruits. After you select the type of lamp you want then you must decide how many systems will be required to cover the planted area.  The following chart shows the coverage area of the available lamp sizes. HPS (High Pressure Sodium) lighting can cost up to 15% more than comparable MH (Metal Halide) systems, however, the bulbs have a longer life span and also have a higher lumen output than any other H.I.D. (High Intensity Discharge) lighting.  MH (Metal Halide) bulbs lose about 15% to 20% of their light intensity after one year where as the HPS (High Pressure Sodium) bulbs lose only about 5% of their intensity in the same time frame. MH (Metal Halide) systems produce between 70 and 115 lumens per watt of electricity consumed, HPS (High Pressure Sodium) systems produce between 97 and 150 lumens per watt.Growers continue to debate over which of these types of H.I.D. (High Intensity Discharge) lighting is the preference for generic use.  But, the rule of thumb is that metal halide light spectrum is best for dense vegetative growth and the high pressure sodium is best suited for blooming growth.  If you are starting to wonder if this article has a specific answer to the question of which is better, well, I'll leave it up to personal preference.  Some people have been known to have a MH (Metal Halide) and a HPS (High Pressure Sodium) lighting system, using the MH (Metal Halide) for the vegetative cycle and then switching over to a HPS (High Pressure Sodium) system when it's time for blooming.  Another option is to use a switchable ballast (available in 1000w MH/HPS and 400w MH/HPS).  These are ballasts that allow the grower the option of using an MH (Metal Halides) or an HPS lamp (High Pressure Sodium), or they can use both (one bulb for a period of time and then switch halfway through the grow period to the other bulb, to simulate the grow seasons).  These switchable systems are slightly less efficient than the normal ballasts, but they are much cheaper than buying an entirely separate system.

Regardless of which system you choose, you should change out your bulbs no later than the end of their rated life; this is due to the loss of intensity and therefore rendering the system less efficient.  MH (Metal Halide) bulbs should be changed after 12 to 18 months and HPS (High Pressure Sodium) bulbs after about 24 months.  This will ensure proper light intensity and therefore proper growth.

Fluorescent Plant Grow Lights

Until recently, fluorescent grow lights have had a low output and have been too big and bulky to be of much use as a grow light for anything more than starting seedlings. Compact and T5 full spectrum fluorescent lights have changed that. At 75 to 90 lumens per watt, these lights are energy efficient and extremely effective especially when used in numbers. Fluorescent grow lights also have better color rendering properties (more of the light emitted is used by the plant) and produce much less heat than incandescent and HID grow lights. This allows them to be placed closer to plants (within a few inches) greatly decreasing lumen loss from the bulb to the plant.

The standard 40 and 20 watt full spectrum tubes are great for starts and seedlings. They are also popular for growing low-light plants like herbs and African violets. These lights are low intensity and need to be placed within 6" (up to 12" for shade loving plants) of the plants to be effective. They are a poor light source for flowering and budding primarily because of their low lumen output.

Incandescent Plant Grow Lights

These lights are good for providing supplemental light to individual house plants or small groups of plants and provide an inexpensive alternative to other grow lights, because they do not require a ballast. Incandescent lights have a low lumen output per watt compared to HID and fluorescent grow lights.

The Cost to Run a Lighting System

To get the operating cost per hour for a light, take the lights combined wattage, and divide it by 1000 to get the kilowatts used. Then multiply that number by the amount your electric company charges per kilowatt hour. HID lights will use the number of watts it emits per hour, ie; 600w system will use 600 watts per hour (regardless of spectrum).

(light wattage output / 1000) x electricity cost per kilowatt hour =
Operating cost per hour operating cost per hour x hours used per month =
Operating cost per month

How the Sunlight Effects Plant Growth

 

200 - 280 nm	UVC ultraviolet range which is extremely harmful to plants because it is highly toxic.
280 - 315 nm	Includes harmful UVB ultraviolet light which causes plants colors to fade.
315 - 380 nm	Range of UVA ultraviolet light which is neither harmful nor beneficial to plant growth.
380 - 400 nm	Start of visible light spectrum. Process of chlorophyll absorption begins. UV protected plastics ideally block out any light below this range.
400 - 520 nm	This range includes violet, blue, and green bands. Peak absorption by chlorophyll occurs, and a strong influence on photosynthesis. (promotes vegetative growth)
520 - 610 nm	This range includes the green, yellow, and orange bands and has less absorption by pigments.
610 - 720 nm	This is the red band. Large amount of absorption by chlorophyll occurs, and most significant influence on photosynthesis. (promotes flowering and budding)
720 - 1000 nm	There is little absorption by chlorophyll here. Flowering and germination is influenced. At the high end of the band is infrared, which is heat.
1000+ nm	Totally infrared range. All energy absorbed at this point is converted to heat.

 

WHY use a GARDENLIGHT for indoor gardening?

Grow lights are usually the most expensive item in the indoor garden, so it's important to choose the right one for your requirements. You should measure the square footage of your garden area, and consider the plants that will be grown. Different plants have different light requirements. Normally, the taller the plant, the more light required in order to reach the lower sections. Plants that flower or fruit typically require more light than those which do not (ie: herbs).

WHAT type of GARDENLIGHT should you use?

FLUORESCENTS are fine for starting seeds or cuttings, but are not powerful enough to light an area more than 8-10" below the bulb. Although more efficient than incandescents, they are still much less efficient than HID light systems. HID (High Intensity Discharge) light systems have revolutionized indoor gardening in the last two decades. They are the most energy efficient grow lights available, so they produce much more light for the amount of power consumed. National Garden Wholesale offers GARDENLIGHTS in MH and HPS. Metal Halide (MH) bulbs emit a light spectrum which appears blue-white to the human eye. This color spectrum is more conducive for vegetative growth, or starting seeds & clones. High Pressure Sodium (HPS) bulbs emit a spectrum which is more concentrated in red/orange light. This color is ideal for the fruiting and flowering stage of a plant's development. It is a good multi-purpose light as well. Larger wattage systems will cover larger growing areas, and since these bulbs produce greater light intensity they are superior for growing taller plants such as tomatoes.

Which GARDENLIGHT is right for me?

Most gardeners use at least 25 watts per square foot of garden space. You may need less if your GARDENLIGHT is used to supplement natural sunlight, or if you are growing a plant that does not require as much light (ie: lettuce). However, many gardeners prefer to double or even triple the recommended wattage to achieve faster growth rates. There is really no such thing as too much light, but using a big light in a small space will sometimes result in high temperatures that are difficult to control. Keep in mind that plants need periods of darkness too. Most indoor gardeners use supplemental lighting from 10 - 16 hrs per day.

Hanging Height

Keep an HID bulb about 30" - 36" above the top of your plants. (This is an average distance...lower wattage bulbs may be placed closer, while higher wattage bulbs may need to be placed further away). Higher wattage bulbs provide more intense light for large growing areas. Lower wattage systems are used for smaller garden areas. Note: the height of the reflector/fixture above the plants will also affect coverage area.

Average coverage area by wattage:

• 150/175 watts - 2' x 2'
• 250 watts - 3' x 3'
• 400 watts - 4' x 4'
• 600 watts - 6.5' x 6.5'
• 1000 watts - 8' x8'

Power Consumption

On average a GARDENLIGHT will increase your electricity cost from $5 to $8 per month-the exact amount depends on the size of the system and the number of hours operated. However, since these grow lights are so energy efficient, you are getting huge amounts of light (and growing power) for your money! Make sure your grow room's power circuit can handle the power draw. For safety reasons, do not exceed 75% of the rated ability of the fuse (for example: use no more than 15 amps on a 20-amp circuit). To calculate your cost, multiply the bulb wattage X hours of operation and divide by 1000. This figure is the number of kilowatt hours of electricity consumed. (Example: a 400 watt bulb running for 18 hours will use 7.2 kilowatt hours). Check your power bill for the cost of each kilowatt hour.

Information about Lamps

The plant sensitivity curve for photosynthesis has its peak at the red end of the spectrum (675nm) (McCree).

This chart indicated that providing plants with the wavelengths best suited to photosynthesis, is the most efficient use of artificial light. Tests show a mean deviation from the average sensitivity curve of less than 5% for a wide variety of plants. The curve shows that the maximum sensitivity for photosynthesis lies in the far red at approximately 675 nm.

The plant sensitivity curve disputes two common misconceptions. The first is that an "ideal" plant growing lamp duplicates the spectral energy distribution of the sun. Sunlight has a continual spectrum, radiating energy in wavelengths that contribute less to photosynthesis, and are therefore "wasted" on the plant. For this reason, many lamps are more efficient than sunlight for plants.

Which Lamp is Best for Your Growing Needs?

Metal Halide Lamps – This type of light is blue-orientated in the spectrum. It's the best type of light to be used as a primary light source (if little or no natural sunlight is available). This type of lamp promotes plant growth.

High Pressure Sodium Lamps – These lamps are red/orange in the spectrum. They are the best lamps available for secondary or supplemental lighting (used in conjuction with natural sunlight). This type of light promotes flowering/budding in plants. It's ideal for Greenhouse/Commercial growing applications.

Conversion Lamps – There are two(2) types of conversion lamps: Sodium Lamps which run on halide ballasts - more common. Halide Lamps which run on sodium ballasts. This type of lamp allows you to tailor the light source to the growth stage of the plant (again, using halide blue light for growth and sodium red light for flowering/budding) merely by changing lamps.

Fluorescent – This type of light is perfect for starts and seedlings but is a poor light source for growth and budding primarily because of low lumen output.

Incandescent – Unlike the other lamps, above, this type does NOT require a ballast. These lamps consist of Sylvania Spot Gro R-20 and R-40 flood lamps available in 75 watt and 150 watt sizes. Also good for starts and seedlings. Good lamp choice for individual plants or small groups of plants. Provides an inexpensive alternative to HID lamps.

Note: Halide and High Pressure Sodium are referred to as "High Intensity Discharge" (HID) Lamps

Lamps > Metal Halide

Metal Halide lamps provide a light that is blue-orientated in the spectrum. It is the best type of light to be used as a primary light source (if little or no natural sunlight is available). This type of light promotes plant growth.

Sunlight provides you with the facts about which type and style of lamp you need to suit your particular home greenhouse or commercial growing application. Our lamps are the highest quality and offer you the flexibility that you want. We can help you choose the best solution for your lighting problem.

Lamps > High Pressure Sodium

Sunlight provides you with the facts about which type and style of lamp you need to suit your particular home greenhouse or commercial growing application. Our lamps are the highest quality and offer you the flexibility that you want. If assistance is needed, we can help you choose.

High Pressure Sodium lamps provide a light that is red/orange-orientated in the spectrum. It is the best type of light to be used as a secondary light source (in conjunction with bluer light or metal halides). This type of light promotes plant fruiting and flowering as it mimicks the natural fall/winter spectral shifts that occur with the changes in the season. It will work as a primary light source, but is more prominently used during the fruiting cycle of you gardens.

Conversion lamps are HPS lamps that are operated with standard metal halide ballasts.

Enhanced Spectrum Lamps are the number one selling horticultural HPS lamps due to thier increased output in the Blue spectrum, giving the best combination of light for both growth, and flowering.

Ballasts

• Ballast Housing - Our Sun System™ brand remote ballasts utilize a heavy duty white powder coated extruded aluminum ballast housing. This method is quieter and dissipates heat better than a sheet metal housing. It is also sealed and keeps moisture and debris out of the unit.
• High Temp Capacitor - Our ballasts come with a high temperature rated capacitor. Most of our competitors using cheaper 85 or 90 degree caps. If there is a component failure in a ballast, 9 times out of 10 you will find it is the capacitor. 100 degree caps are more expensive, but they can vastly increase the life and reliability of a system.
• Transformer - The light systems we manufacture use only the highest quality, domestic name brand ballasts and components. (The Sun System X utilizes a high quality import system, but retains the domestic high temp capacitor as a standard).
• UL Listed - We have gone to great lengths to insure our products are safe and reliable.Underwriters Laboratories (UL) sets the standard for fixture testing. They conduct extensive tests before giving their seal of approval on a product, making sure it complies with their strict standards. All systems are UL listed (with the exception of the SS X).
• Detachable Lamp Cord Set - Our system offers the convenience of the detachable lamp cord. This allows you to easily seperate hood from ballast for mobility and ease of maintenence. Some competitors have products that are hard wired, and often difficult to work with.
• Sockets - Our univeral socket assembly offers 2 distinct advantages over conventional sockets: One, it's compatible with our entire line of reflectors, both horizontal and vertical. Two, it's the industry's only custom-made 5 kv/hor socket exclusively made for Sunlight Supply.

Reflectors

The type and style of reflector that you choose can make the difference between a poor result and a superior growing experience! Sunlight Supply manufactures several different horizontal reflectors to ensure that you get the correct reflector for your particular gardening needs and requirements. We also manufacture eleven different vertical reflectors, ranging in size from 2 feet to 7 feet, with your choice of parabolic, cone or deep cone to maximize plant growth.

Most all of our horizontal reflectors come with a 95% reflective, textured aluminum insert. These hoods will have far better performance than the competitors hoods that use a 87% reflective spectral pebble insert.