Home » A Guide to Supplemental Greenhouse Lighting

A Guide to Supplemental Greenhouse Lighting

by Dany

In this comprehensive guide, we delve into the intricate world of supplemental lighting systems for greenhouses, a pivotal component in optimizing crop yields and quality. As seasoned cultivators navigate the ever-evolving landscape of controlled environment agriculture, the strategic implementation of artificial illumination has become an indispensable tool. Whether combating the challenges of seasonal fluctuations or enhancing specific growth phases, supplemental lighting offers a powerful solution to maximize production efficiency.

Understanding Light Measurement Units

To effectively harness the potential of supplemental lighting, it is crucial to grasp the units employed in quantifying light intensity. The preferred unit for measuring light in plant production is µmol m-2 s-1 (pronounced “micromol per meter squared per second”). This unit represents the amount of light particles (photons or quanta) incident on a unit area (m2) per unit time (second). Specifically, it measures the Photosynthetically Active Radiation (PAR) waveband, ranging from 400 to 700 nanometers (nm), which plants utilize for photosynthesis.

Quantum sensors, meticulously designed with filters to exclude light outside the PAR waveband, are the instruments of choice for accurate PAR measurements. While foot-candle meters (or lux meters) can measure light in a slightly broader waveband (approximately 380-770 nm), their readings may introduce slight errors when evaluating the light environment for plant production. Therefore, the use of quantum sensors is highly recommended for precise PAR quantification.

Lamp Technologies: Metal Halide and High-Pressure Sodium

Among the most efficient lamps employed for supplemental greenhouse lighting are the high-intensity discharge (HID) lamps, specifically metal halide (MH) and high-pressure sodium (HPS) lamps. MH lamps emit a more white-colored light, while HPS lamps produce a yellowish-orange hue reminiscent of street lamps.

HPS lamps boast a slightly higher efficiency in converting electrical energy into PAR light and offer an average rated lamp life up to three times longer than their MH counterparts. However, MH lamps provide a higher proportion of blue light, which is crucial for proper crop development in certain species.

Due to their superior efficiency and extended rated lamp life, HPS lamps are the predominant choice for supplemental lighting in commercial greenhouse operations. Common wattages for these lamps range from 400 to 1,000 watts.

Installation Considerations for Optimal Performance

When implementing supplemental lighting systems in greenhouses, several factors demand careful consideration to ensure optimal performance and cost-effectiveness:

  1. Solar Radiation Analysis: Evaluating the average solar radiation levels for the specific location is imperative. This assessment provides insights into the range of solar radiation conditions at the site, enabling informed decision-making. The National Renewable Energy Laboratory’s (NREL) database offers solar radiation data for numerous locations across the United States and its territories, facilitating the conversion of this data into the mol m-2 d-1 unit (daily sum of light available for photosynthesis).
  2. Greenhouse Structure and Equipment: The type of greenhouse structure, glazing materials, and installed equipment can significantly impact the transmission of sunlight, influencing the supplemental lighting requirements.
  3. Crop Requirements: The specific crop(s) grown in the greenhouse dictate the plant’s light intensity, duration, and light integral needs, shaping the supplemental lighting system design.
  4. Available Space: The available space within the greenhouse for hanging lamps directly affects the uniformity of supplemental lighting distribution. Limited vertical clearance in lower greenhouses can compromise uniform light distribution for taller crops.
  5. Plant Requirements vs. Solar Availability: By comparing the plant’s light requirements with the available solar radiation levels, growers can accurately calculate the necessary supplemental lighting intensity and duration.

Optimizing Light Intensity and Duration

In most cases, it is not economically feasible to install supplemental lighting systems that provide excessively high light intensities due to the substantial number of lamps required. Consequently, these systems are typically designed to deliver a specific light integral during a 24-hour period, ensuring that the combined supplemental light integral and solar radiation integral meet the plant’s daily light requirements, even on the darkest day of the year.

The light integral supplied by the supplemental lighting system depends on the average light intensity provided by the lamps and their operational duration. Commercial supplemental lighting systems typically do not exceed an intensity of 200 µmol m-2 s-1 (0.72 mol m-2 hr-1 or 17.3 mol m-2 per 24-hour period).

Achieving Uniform Light Distribution

In addition to light intensity, uniform light distribution across the crop canopy is a critical factor in supplemental lighting system design. While sunlight generally provides uniform illumination within a greenhouse (barring cloud cover or structural shading), supplemental lighting systems inherently create non-uniform patterns due to the distance between lamps and the crop.

Designers employ sophisticated computer software programs to optimize light uniformity by meticulously calculating the light distribution from each lamp and the various paths the light can travel to reach the crop beneath. Careful design ensures acceptable light distribution and uniformity over the crop canopy.

Supplemental Greenhouse Lighting for Cannabis Cultivation

Greenhouse Lighting is used in cannabis cultivation and when it comes to cultivating famous strains like the Pineapple Express strain, supplemental greenhouse lighting plays a crucial role in enhancing the plant’s growth and ensuring a bountiful yield. 

The Pineapple Express strain thrives under optimal lighting conditions, and supplemental greenhouse lighting provides the necessary boost during periods of low natural light. By implementing a well-designed supplemental lighting system, growers can maintain consistent light levels throughout the plant’s growth cycle, promoting vigorous vegetative growth and abundant bud production.

One of the key benefits of the Pineapple Express strain is its ability to produce a high yield of dense, resinous buds with a delightful pineapple aroma and flavor. With the aid of supplemental greenhouse lighting, growers can maximize the strain’s genetic potential, ensuring a bountiful harvest of top-quality buds.

Reflector Considerations

Most supplemental lighting units incorporate reflectors designed to direct the light generated by the bulb downward onto the crop. Different manufacturers utilize diverse materials and designs, aiming to efficiently direct and evenly spread the light over the crop area.

However, it is essential to strike a balance between reflector size and potential solar radiation blockage. Excessively large reflectors may obstruct significant amounts of natural sunlight from reaching the crop. Additionally, reflectors installed in greenhouses tend to accumulate dirt over time, necessitating periodic cleaning to maintain optimal reflectivity.

Off-Peak Operation for Cost Optimization

To enhance the economic viability of supplemental lighting systems, growers often operate these systems exclusively during off-peak electricity rate periods, typically from 10 p.m. to 6 a.m. However, during the darker months, this strategy may result in two distinct light periods for the crop within a 24-hour cycle: one period beginning at sunrise and ending at sunset, followed by a short dark period, and another period continuing with supplemental lighting, succeeded by a brief dark period before sunrise.

It is crucial to consider that not all crops thrive under these conditions, as some may require an extended dark period (e.g., tomatoes). In such cases, supplemental lighting may need to be utilized during hours with more expensive electricity rates. Careful computer control of the lighting system’s operation can help reduce operating costs by optimizing the timing and duration of supplemental illumination.

Maintaining Consistent Daily Light Integrals

For certain crops, particularly during the vegetative growth phase, a linear relationship exists between the total amount of light received and plant growth. This relationship has given rise to the concept of providing plants with a consistent daily light integral (or light sum) throughout the year, irrespective of the amount of solar radiation received.

Whenever the sunlight alone is insufficient to meet the target light integral, supplemental lighting systems compensate for the deficit. Conversely, when the crop is at risk of receiving more than the target light integral, shade curtains are deployed to regulate the light exposure.

Maintaining a consistent daily light integral requires sophisticated computer software to monitor the amount of light received since sunrise, compare it with predicted total sunlight at sunset, and determine the optimal operation of the lighting or shading systems. This approach not only ensures a consistent light integral but also maximizes the utilization of off-peak electricity hours for supplemental lighting, further enhancing cost-effectiveness.

Carbon Dioxide Enrichment for Enhanced Photosynthesis

Photosynthesis, the fundamental process driving plant growth, requires not only light (PAR) but also carbon dioxide (CO2) in sufficient quantities. When supplemental lighting is employed to increase plant production, maintaining adequate CO2 concentrations within the greenhouse becomes crucial to prevent CO2 from becoming a limiting factor.

During the colder months, when greenhouse ventilation rates are minimal to maintain desired temperatures, the CO2 concentration inside can drop significantly due to limited fresh air exchange. Under these low-ventilation conditions, it may be economically viable to enrich the greenhouse atmosphere with CO2 levels up to three times the ambient concentration, resulting in increased photosynthesis and enhanced plant growth.

Research indicates that, within certain limits, it is possible to reduce the required daily light integral while simultaneously increasing the CO2 concentration, achieving the same overall plant production. This strategy highlights potential significant savings, as CO2 enrichment is typically more cost-effective than adding supplemental light.

Computer control software plays a pivotal role in assisting growers with CO2 enrichment decisions, including when to introduce CO2, determining target concentrations, and coordinating the operation of supplemental lighting systems. However, during warmer months with substantial ventilation requirements to maintain target greenhouse temperatures, CO2 enrichment may not be cost-effective due to the rapid exhaust of the released CO2.

Proactive Lamp Replacement and Maintenance

Proper maintenance of supplemental lighting systems is imperative and should never be overlooked. Like any other equipment, failures can occur, necessitating prompt correction to prevent non-uniform light distribution patterns that can adversely affect plant production uniformity.

In addition to incidental failures, the light output of lamps gradually degrades over time, with the rate of degradation varying based on the lamp type and operating conditions (e.g., temperature). By understanding the approximate rate of degradation (consult the manufacturer’s specifications), growers can develop a strategic lamp replacement schedule to ensure that the overall light intensity does not drop below an acceptable minimum level.

Instead of replacing all lamps simultaneously, which can be cost-prohibitive, a staggered approach can be adopted, such as replacing lamps in groups (e.g., one greenhouse bay at a time or every other lamp or every third lamp). This proactive maintenance strategy ensures optimal light output while minimizing operational disruptions and costs.


Mastering the art of supplemental greenhouse lighting is a transformative journey for cultivators seeking to optimize crop yields, quality, and production efficiency. By harnessing the power of artificial illumination, growers can transcend the limitations imposed by seasonal fluctuations and environmental challenges, unlocking a realm of unprecedented control over the cultivation process.

Through a comprehensive understanding of light measurement units, lamp technologies, installation considerations, light intensity optimization, uniform distribution, reflector design, off-peak operation, consistent daily light integrals, carbon dioxide enrichment, and proactive maintenance, cultivators can navigate the intricate landscape of supplemental lighting with confidence and precision.

As the demand for high-quality, sustainable produce continues to soar, the implementation of supplemental greenhouse lighting systems emerges as a pivotal investment for forward-thinking growers. By embracing this technology and integrating it seamlessly into their operations, cultivators can position themselves at the forefront of the controlled environment agriculture revolution, reaping the rewards of increased yields, enhanced quality, and long-term profitability.

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