When setting up an indoor greenhouse, one of the most important considerations is lighting. Unlike outdoor greenhouses which rely on natural sunlight, indoor greenhouses need artificial grow lights to provide enough light for plants to grow successfully. But do you really need special grow lights, or are standard light bulbs sufficient? Here we’ll examine the pros and cons of grow lights for indoor greenhouses.
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What are grow lights?
Grow lights are specialized electric lights designed to stimulate plant growth by emitting wavelengths of light that are useful for photosynthesis. There are several different types of grow lights including:
- Fluorescent lights – Standard fluorescent tubes or compact fluorescents that emit light in the blue and red spectra.
- LED lights – Energy efficient LEDs that can be tuned to specific wavelengths for horticulture.
- High intensity discharge (HID) lights – Includes metal halide and high pressure sodium lights that produce intense light.
- Incandescent lights – Standard household light bulbs that emit some red and blue light.
Grow lights are designed to provide more of the red and blue wavelengths that chlorophyll uses for photosynthesis. They help compensate for the lack of natural sunlight indoors. Many grow light systems allow the spectrum, intensity and photoperiod (length of daily exposure) to be customized for the plants you want to cultivate.
Benefits of using grow lights
Here are some of the key benefits of using specialized grow lights in an indoor greenhouse:
- Greater light intensity – HID and some LED grow lights produce more intense light per square foot than standard bulbs. This allows plants to photosynthesize more efficiently in the limited space of an indoor greenhouse.
- Customizable spectrum – Most grow lights allow you to select specific wavelengths and ratios of red, blue, green, etc. light. You can tailor the spectrum to your particular plants.
- Energy efficiency – Newer LED grow lights provide light optimized for plant growth while using much less electricity than older technologies like high pressure sodium lamps.
- Directional lighting – Many grow light systems have adjustable mounts and reflectors to direct light right where it’s needed. This allows you to maximize light utilization.
- Runs cooler – LED and fluorescent lights run cooler than HID lights. This helps prevent heat damage to plants.
- Long lifespan – LED grow lights can have a lifespan of 50,000 hours or more before degrading significantly. Other types last 10,000 to 20,000 hours typically.
By providing customizable, high intensity light optimized for plant growth, grow lights allow indoor gardens to thrive like never before. The ability to tune the spectrum is especially beneficial when growing a variety of different crops in one greenhouse.
Downsides of grow lights
Of course, installing specialized grow lights also comes with some potential disadvantages:
- Higher upfront cost – Quality LED or HID grow light systems can cost hundreds to thousands of dollars to install. Fluorescent grow lights are more affordable.
- Complex setup – To get the full benefit, grow lights need adjustable mounts, reflectors, timers, etc. This increases the complexity versus using simple light bulbs.
- Supplemental heating often needed – Most grow lights emit very little infrared radiation that provides warmth. You’ll likely need heaters to maintain ideal temperatures.
- Improper use can damage plants – Excess intensity, improper spectrum and incorrect mounting height/angles can stress or damage plants if not set up properly.
- Higher electricity usage – While LEDs offer vast improvements, indoor gardens still typically use significantly more electricity for lighting than conventional household lighting.
For small indoor greenhouses, dealing with the cost and complexity of grow lights may not make sense. But their advantages outweigh the disadvantages for larger growing areas of 100+ square feet.
What about standard light bulbs?
Can you get by with standard incandescent or fluorescent light bulbs in an indoor greenhouse? Here are some considerations:
- Standard bulbs emit more green and yellow light. Plants use red and blue light more efficiently for photosynthesis.
- Incandescent lights waste energy producing heat. Around 95% of their energy output is infrared heat rather than visible light!
- Fluorescent tubes or compact fluorescents run cooler and more efficiently. They last longer too.
- You’ll need many more standard bulbs to match the intensity of HID or high power LED grow lights.
- With standard bulbs, it’s harder to customize the spectrum and control the photoperiod.
- Standard bulbs provide light over a broader angle. More is wasted lighting non-plant areas.
Here’s a quick comparison of some key factors:
| Light Source | Typical Wattage | Lifespan (hours) | Light Intensity | Heat Output |
|---|---|---|---|---|
| Incandescent bulb | 60W | 1,000 | Low | High |
| CFL bulb | 13W (60W equivalent) | 10,000 | Medium | Low |
| HID grow light | 400W | 20,000 | Very high | High |
| LED grow light | 200W | 50,000+ | Medium-high | Low |
Standard bulbs can provide adequate supplemental lighting for starting seedlings or very small growing areas. But for serious indoor gardening, the intensity and spectrum control of grow lights really make a difference in plant health and productivity.
Choosing grow lights for an indoor greenhouse
If you’ve decided to install grow lights in your indoor greenhouse, here are some tips for choosing appropriate systems:
- Match lumen output to growing area size. Aim for 3,000-5,000 lumens per square foot for fruiting plants.
- For a mixed garden, look for broad spectrum LEDs or a combo of HPS and MH lights.
- Position overhead lights 2-4 feet above plants. Angle reflectors for even coverage.
- Check that lights have a sealed ballast and are rated for damp locations.
- Install lights on pulleys so you can raise them as plants grow taller.
- Get lights with timers and dimming capabilities to control photoperiods.
- Do some research to pick lights optimized for your particular crop types.
- Factor in energy efficiency – electricity costs add up for grow lights!
With LED technology improving all the time, you can now get excellent plant growth with greater electricity savings. Just be prepared for the initial investment in a quality lighting system.
Conclusion
Installing grow lights in an indoor greenhouse provides major benefits compared to relying on standard light bulbs:
- More light intensity and optimized spectrum for photosynthesis.
- Fully customizable lighting periods and conditions.
- Energy savings with new LED fixtures.
- Ability to tailor lighting to the exact crops you want to grow.
While grow lights require a greater upfront investment, they typically pay for themselves over time through faster, more abundant plant growth and higher productivity in the limited space of an indoor greenhouse. For greenhouses larger than 100 square feet, the advantages of grow lights far outweigh relying on standard bulbs. Carefully designed grow light systems allow indoor gardens to thrive year round!
Additional Considerations
Here are some additional points to consider when setting up lighting in an indoor greenhouse:
- Make sure lights are fully waterproof and designed for high humidity environments.
- Install reflective surfaces on walls to maximize light utilization.
- Position lights on adjustable hangers so they can be moved vertically as plants grow.
- Track electrical load – larger grow lights use considerable power.
- Consider glass or polycarbonate glazing to allow beneficial UV light transmission.
- Setup proper ventilation and dehumidification to remove excess heat from lights.
- Supplement grow lights with adjustable LED spotlights over specific plants as needed.
- Make sure lights don’t leak outside and bother nearby homes/businesses.
- Consider special fixtures like intracanopy lighting for multilayer gardens.
- Monitor plant health and adjust lighting duration, intensity and spectrum as needed.
With some careful planning and testing, you can create a highly customized indoor lighting environment that enables plants to thrive with abundant healthy growth and maximum yields from your available space. Grow lights open up exciting possibilities for serious year-round indoor food production!
Example Grow Light Setups
Here are two example grow light configurations for a hypothetical 200 square foot indoor greenhouse:
Budget Fluorescent Setup
- Ten 4-foot 54W T5 high output fluorescent fixtures.
- Mounted 1 foot above seedlings, 2 feet above larger plants.
- Mixed spectrum 5000K and 2700K tubes.
- Manual operation – turned on 14 hours/day.
- 400W of grow light capacity.
- Approx. $300 in startup costs.
High-end LED System
- Two 450W full spectrum LED grow lights.
- Linked to programmable timer and pulley system.
- Adjustable mounting height from 1-4 feet.
- Automatically provides 16 hours of light per day.
- 900W of grow light capacity.
- Approx. $1,500 in startup costs.
This example illustrates how a higher startup investment in LEDs pays off with more automation, twice the lighting power, and the ability to finely tune conditions for each stage of plant growth. The energy savings and improved plant growth can ultimately more than make up for the higher initial cost.
Comparative Electricity Usage
One major consideration with indoor grow lights is the operating cost from electricity usage. Here is an example comparing the estimated electricity costs of different grow light options for the same 200 square foot greenhouse over the course of one year:
| Lighting Setup | Wattage | Hours/Day | kWh/Year | Electricity Cost/Year |
|---|---|---|---|---|
| CFL Bulbs | 500W | 12 | 2,190 | $328.50 |
| HPS Grow Lights | 1,000W | 14 | 5,110 | $766.50 |
| LED Grow Lights | 900W | 14 | 4,599 | $689.85 |
Assuming an average electricity rate of $0.15/kWh, the low efficiency CFL setup would cost over $300 per year. The more powerful HPS lights cost over $760 annually, while an energy efficient LED system still costs close to $700 per year. The initial LED investment may pay for itself in just a few years of electricity savings compared to other options.
Greenhouse Lighting Plans
When installing grow lights in a greenhouse, it helps to develop a detailed lighting plan. Here are some tips for creating an effective plan:
- Make a greenhouse layout diagram showing dimensions and shelving/growing areas.
- Research lighting needs for each crop you want to grow.
- Select appropriate grow lights and map where each will be located.
- Calculate total wattage and verify electrical service is sufficient.
- Plan mounting heights and adjustments for plant growth stages.
- Design optimal light coverage for the entire space.
- Factor in reflective surfaces to maximize light utilization.
- Develop schedules for photoperiods tailored to each crop.
- Choose automated lighting control systems if within budget.
A good lighting plan optimizes spectrum, intensity, spacing, height and exposure durations to provide ideal conditions. This takes some research and planning, but the effort can really maximize plant health and productivity.
Lighting Maintenance
Here are some tips for maintaining an indoor greenhouse lighting system:
- Check lights regularly for burned out diodes/tubes and replace promptly.
- Clean dust and dirt buildup off lights – this degrades intensity.
- Watch plant health for signs of too much/too little light exposure.
- Adjust mounting heights as plants grow taller.
- Monitor humidity and temperature – excess heat shortens light lifespan.
- Check for wiring damage from moisture or pests.
- Verify timer and photoperiod settings periodically.
- Record hours used for LEDs/HPS/MH lights and replace per manufacturer recommendations.
- Consider intensity testing with a PAR meter annually, replace lights as needed.
With periodic inspection and care, a quality lighting system should provide many years of optimal light for indoor plant growth and food production in your greenhouse.