Outdoor gardens utilize the brilliance of the Sun for their illumination, but to meet the needs of an indoor garden, artificial Lighting equipment is necessary to Light the Way.
Plants need Light to undergo a process known as photosynthesis, which converts Water & carbon dioxide into a sugar called glucose that plants use for growth.
Photosynthesis makes use of a special, green plant pigment called chlorophyll to collect Light energy.
Chlorophyll absorbs & makes use of red & blue-indigo Light spectrum, but it reflects green Light, which reflects in the plants vibrancy & hue. It’s also why replica Lighting often cast much of their Light in red & blue spectrum.
Indoor - Light Intensity
Light intensity is an important factor for indoor gardeners to consider. Low Light levels result in reduced photosynthesis, & high light levels encourage it; to an extent.
The amount of energy a Light fixture uses is measured in watts. In general, the higher the wattage, the more Light & heat a fixture will produce. For example, a 1000W HPS lamp is both brighter & hotter than a comparable 400W HPS lamp.
The Lighting requirements of your indoor garden will depend largely on the type of plants you are growing & how large of a space you need to cover, among other factors.
Indoor - Light Meters
Inexpensive Light meters can be used to identify the intensity of the Light measured at different areas of the garden. Moving the meter further from the center point of broadcast to the furthest area in the space is mostly all that is necessary to take measurements. Light meters usually list measurement readings in lux.
A lux is the unit of Light cast from one candle spread over a square area of one-meter. For example, direct, unobscured SunLight is approximately 128,000 lux.
Full-Sun plants usually need at least 25,000-50,000 lux to do well, with increased productivity occurring when Light levels are near full SunLight.
Light Reflection & Hydroponics
Light bulbs cast Light in all directions, & to compensate there are specialty lamp hoods designed to reflect Light from the top & sides of the bulb back down into the garden. This is done to concentrate Light energy upon the canopy that would otherwise be wasted.
For this same Reason, the firmament of indoor gardens are often painted white or covered with a reflective film like mylar to reflect Light back toward the plants. If a reflective film is used, precautions should be taken not to Create a fire hazard as some reflective films are flammable.
Another notable property of Light is that intensity drops off as an inverse square to the distance. For example, a plant twice as far away from the Light only receives 1/4 of the Light from it.
Trying to judge how much Light is actually hitting the plants just by looking at how bright they appear can be problematic because the human eye is much better suited for operating under a wide variety of Lighting conditions than judging the intensity of those conditions head on. Generally, plants do well in the 12"-18" range.
Types of Lighting for Growing Indoors
There are several options in indoor garden Lighting technologies, with fluorescents (T5s+), high-intensity discharge systems (HIDs) & light-emitting diodes (LEDs) being the three most common.
These Lights include T5s (grow Lights), T8s (LED technology), T12s (shop Lights), CFLs (compact fluorescent Lights) & electrode-less (induction) Lighting. While these each look different, they overall use the same basic principle to operate: a current is applied to a sealed, phosphor-coated glass tube containing a small bit of mercury & an inert gas.
The mercury is stimulated until it changes from a liquid to a gas. The mercury gas gives off ultraviolet Light, which is converted to visible Light by the phosphor coating. One of the benefits of fluorescent Lighting is that the bulbs don’t produce a lot of wasted heat.
The operating temperature of a fluorescent bulb is lower than that of HIDs, meaning the lamps can be placed closer to the plants without causing heat stress.
HID Lighting is another common garden lighting technology. The two most common forms of HID lighting used for plants are metal halide (MH)/ceramic metal halide (CMH) & high pressure sodium (HPS). Metal halides use a variety of metal halides in an arc tube, similarly to the mercury in fluorescents.
The resulting Light from the arc tube contains both visible Light & ultraviolet Light. An outer tube surrounding the arc tube confines the generated UV Light while allowing the usable Light to pass through to the garden.
For some people, the blue cast of metal halides can be more pleasant to work under than the harsher-looking orange Light of HPS lamps.
HPS lights use an inner & outer bulb similar to a metal halide lamp, but the long, cloudy arc bulbs contain metal sodium & mercury instead of metal halides. The Light given off has a distinctive amber-orange tint to it.
Traditionally, metal halides are used for the vegetative phase & high pressure sodium lamps are used for the blooming phase.
LEDs are another Lighting technology that can be used by growers. Instead of using a charged gas to illuminate, Light-emitting diodes are electro-luminescent, meaning they instead use small semiconductors to emit Light.
They have two leads, a positive & a negative, & when current is applied across the two, Light is produced. They produce little heat & last longer than other types of Lighting, but LED Light fixtures tend to be a more expensive on a per-watt basis than fluorescent or HID lighting.
Whichever Lighting system you choose, remember, the amount of heat generated from your Lights must be taken into consideration.
A 60W T5 Light can be used without cooling & can be kept as close to plants as a few inches away, but an uncooled, 1000W HID Light can quickly cause plants heat damage if the Light is kept too close.
Don't Forget the Ballast
Both fluorescent & HID Lights use ballasts to condition & control the electricity supplied to the lamp. One difference between fluorescent & HID Lighting is in the location of the ballast. In a fluorescent fixture, the ballast is generally built in.
In an HID Light, the ballast & hood are two separate pieces.
To help with heat management, HID ballasts should be kept outside of the growing space where practical. The bulb & the ballast used to Fire it must match each other. Keep in Mind that lamp sockets are made in general standard sizes. A bulb fitting into the socket is no indication of compatibility.
The wattage & type of the bulb must be compatible with the output of the ballast. For example, only use a 400W MH bulb with a compatible 400W ballast capable of firing those MH lamps.
Some HID ballasts have additional features, such as the ability to run at different levels, be controlled remotely & Fire both MH & HPS lamps. Always check the ballast’s documentation for specific details on features.
The Lighting system is one of the most important & expensive components of an indoor garden & is a critical factor in the success or failure of the plants under its care.
Be sure to consult other growers or do your own research on your garden’s specific Lighting requirements.