Greenhouse Film for Hot Climates: Light, Heat and Specification Checks

1. Define the heat problem before choosing a film

Replace a broad description such as “a very hot country” with the conditions during the actual crop cycle. A dry summer site, a humid tropical site and a location with hot afternoons but cool nights do not present the same design problem.

• Location and season: record the site, planting and harvest months, hot-weather temperature and humidity, and whether the cover stays in place through a darker season.
• Crop requirements: identify the crop, growth stage, production objective and acceptable temperature and light conditions with the grower or crop adviser.
• Structure and operation: describe the span, height, single or double cover, vents, screens, shade system, fans and any evaporative cooling.
• The observed problem: distinguish high air temperature, uneven crop exposure, a hot end of the house, or insufficient light during cloudy weather. Record where and when it occurs.

For basic material choices, use the greenhouse plastic selection guide. The additional task here is to turn a climate concern into a measurable cover specification.

2. Do not treat every “IR” or “diffused” film as a cooling film

UMass Extension distinguishes films that reduce daytime heat gain from films that reduce nighttime radiant heat loss. These are different functions. An “IR” label is therefore a reason to ask for details, not enough information to approve a warm-climate project.

On a small screen, scroll the table sideways to read all columns.

Photosynthetically active radiation (PAR) is the light band commonly measured for photosynthesis; traditional PAR measurements cover 400–700 nm. Daily light integral, or DLI, adds up photosynthetic photon exposure over a day; it is not interchangeable with a single midday reading. Apogee's measurement guidance also distinguishes traditional PAR from extended-PAR instruments. Record the sensor's band and units when comparing results.

Haze and transmission must be read separately. ASTM D1003-21's public scope addresses haze and luminous transmittance, not a crop-specific PAR measurement. Do not relabel a luminous-transmittance result as PAR, or calculate shade percentage as “100 minus haze.” The applicable method must suit the material being tested.

If the immediate choice is between clear and white-looking covers, the white versus clear greenhouse film comparison explains that distinction. Appearance alone is not a substitute for optical data.

3. Read the sample identity before reading the performance claim

A useful report connects a result to a specific film. Ask for the grade, tested thickness, sample condition, test method and wavelength range. For transmission, clarify whether the result measures direct or total transmitted light. If a supplier provides only a headline percentage, keep the comparison open until its meaning is explained.

The public ASTM description shows why geometry and procedure matter for haze and luminous transmission. A number from a different method or specimen should not silently become a like-for-like ranking. This is a purchasing check, not a claim that all suppliers must use one test standard.

For a purchase, request the production-grade report rather than assuming that a development sample, a different thickness or another supplier's published trial represents the offered roll. Ask which values are typical, which are contractually specified and what tolerances apply.

A quick quote-review example

• The quote says only “IR film”: mark the function as unconfirmed and ask whether it refers to incoming solar radiation or outgoing long-wave heat.
• The report names a waveband but tests another grade: request evidence connecting that sample to the offered construction before using its values.
• Grade, thickness and method match the offered film: move on to comparing the values with your crop requirements and trial plan. A traceable report is a starting point, not proof of suitability by itself.

4. Match the cover to the climate and cooling system

Hot and dry conditions

Review solar heat control alongside the crop's light needs and the available cooling system. Direct evaporative cooling depends on the incoming air's wet-bulb temperature and system efficiency. UF/IFAS explains these limits; a film does not remove the need to size, operate and maintain the cooling equipment correctly.

Hot and humid conditions

At the same outside dry-bulb temperature, more humid air leaves less potential for direct evaporative cooling. Do not copy an arid-climate result onto a humid site. Ask the greenhouse designer to review airflow, cooling capability and crop conditions together before relying on a new cover.

Hot afternoons with cool nights or a cloudy season

Include night temperatures and lower-light months in the decision. Ask whether daytime heat management, nighttime retention or a combination is required, and request evidence for each claimed function separately. A fixed optical choice should not be judged only on the hottest afternoon of the year.

UMass ventilation guidance describes the roles of wind, vent openings and system operation. Have the actual vent and screen arrangement assessed; film selection cannot establish that air exchange is adequate.

Shading is a separate design decision. Its placement and operation affect both light and heat, so coordinate it with the cover and crop plan rather than automatically combining maximum shading with the lowest-transmission film. UMass's shade-for-cooling guidance discusses how shading is used within the greenhouse system.

5. Build a specification that suppliers can compare

Send the same project brief to each supplier. Keep missing information marked “to confirm” instead of treating it as zero or assuming that an attractive product name answers the question.

Keep durability and cooling claims separate. UMass identifies sunlight, heat, structural contact and chemical exposure among relevant film-life considerations; a UV-stabilized designation does not establish a particular cooling result. The greenhouse film thickness guide covers thickness selection separately.

6. Plan a trial that can answer the purchase question

Before replacing the full cover, agree what the trial must show. A comfortable visit or one favorable thermometer reading is not a sufficient basis for a seasonal purchase.

1. Identify the comparison. Record the reference cover and candidate grade, thickness, installation date and condition. Keep the structure, crop stage and operating settings as comparable as practical.
2. Record the weather. Log outside temperature and humidity at the same times as greenhouse measurements. Where practical, also record outside PAR so changes in available sunlight are visible. Include challenging sunny periods and representative lower-light conditions.
3. Measure where the crop is. Use suitable, radiation-shielded air-temperature sensors at consistent crop-level locations. Record positions rather than moving instruments to whichever spot gives the preferred reading.
4. Track light over time. Use suitable quantum sensors and data logging to integrate readings across the day. Keep the sensor waveband, position and recording period consistent between comparisons. This describes crop light exposure in the greenhouse, not a laboratory measurement of film transmittance.
5. Log system operation. Record vent and shade positions, fan and cooling operation, irrigation changes and unusual events alongside the measurements.
6. Review both benefits and trade-offs. Compare heat management, crop light availability and operational demands. Investigate differences before approving the production order.

UF/IFAS documents temperature gradients between cooling pads and other parts of a greenhouse, and the importance of representative sensor placement. A pad-outlet reading should not be presented as the temperature throughout the crop. See the temperature-gradient and controls sections.

If covers are tested in different houses or on different dates, record that limitation. Observed differences may include weather, structure and management effects. This proposed trial checklist is not a report of tests already conducted by TIAN FENG.

7. Turn the findings into a useful inquiry

Start with the project requirements rather than asking for “the strongest cooling film.” You can adapt this brief:

If a performance field is unavailable, say so in the comparison. It is better to resolve a missing test definition before ordering than to discover that two attractive percentages described different measurements.