Glass Glossary

Plant Growth


Last Updated: November 23, 2023

The most important effect of a glazing system on plant growth is its influence on photosynthesis. Light which drives photosynthesis is called photosynthetically active radiation (PAR) and falls in the spectral range from 400 nm to 700 nm (see Figure 2-39). In essence, the higher the light transmission in the spectral range from 400 to 700 nm, the better the glass product is for plant growth.

House plants often grow under conditions which are marginal for adequate growth, and are primarily selected because of their ability to grow in relatively low light. Not all house plants are equally well adapted to low light conditions; however, some will be stressed by reduced light environments. Factors such as distance from windows, length of exposure to direct sunlight, time of day of direct exposure, light reflection from interior and exterior surfaces, average ambient temperature, temperature fluctuations, relative humidity, air circulation patterns, watering, and perhaps most important of all, the cleanliness of the windows, all have potential impact on plant growth. Dirty windows can be a significant problem in greenhouses due to the reduction in light transmission. The same is undoubtedly true for other buildings in which plants are grown. Light supply problems are most apt to be observed in November, December and January, when the days are short and cloud cover is prevalent.

Unlike field crop plants, house plants have the ability to grow in relatively low light conditions.

The table below lists the percentage of photons transmitted in the PAR region per Cardinal’s LoĒ™ coating. The majority of the listed coatings will have minimal effects on plant growth. A small number of coatings cause the level of photons in the PAR spectrum to fall to or below 50% of the light to be transmitted through an insulating glass IG unit, which is equivalent to the amount of light produced during a bright overcast day. Therefore, on cloudy days the rate of photosynthesis could fall to levels which would noticeably slow plant growth. If in- ternal light intensities are marginal, then the use of this coating in an (IG) unit could result in the inability to grow some house plants.

IG Unit (3mm glass) Percentage of Photons Transmitted in PAR Spectral Region
Clear / Clear
83%
Clear / LoE-i89
81%
Clear / LoE Di89
80%
Clear / LoE-180
73%
LoE-272 / Clear
71%
Clear / Clear
83%
Clear / LoE-i89
81%
Clear / LoE Di89
80%
Clear / LoE-180
73%
LoE-272 / Clear
71%

Figure 2-35: IG Unit (3mm glass) in relation to Percentage of Photons Transmitted in PAR Spectral Region.