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House plant near window

Is coated glass bad for indoor plants

31 May 2017
‘Will windows be bad for my indoor plants?’ isn’t a question frequently put to installers or insulating glass unit (IGU) manufacturers. However, it’s an important concern when specifying glazing for orangeries, atria, or plant enthusiasts.
We’ve recently fielded enquiries about the impact the increased use of low-emissivity, solar control and strongly tinted glass has on plant growth, while coated glass isn’t necessarily bad for indoor plants, it’s important to remember plants flourish behind glass for various reasons.

These include the type of plant, the percentage of daylight transmitted through the glazing, the internal room temperature and humidity where it is located. 

Clear, neutral glass with high light-transmittance

Plants grow best behind glazing that has a neutral daylight transmittance.

Most of the important photochemical processes in a plant use the blue and red areas of the visible light spectrum. Red light stimulates stem and leaf growth, while blue light regulates plant enzyme and respiratory processes, and encourages low, stocky growth and dark green leaves. Providing plants with the right balance of red and blue light is key to successful indoor plant growth, therefore glass without a dominant colour should be specified if plant life is a concern.

In the Pilkington family, Pilkington Optiwhite™ allows the most natural light through, with 92 per cent of daylight transmitted through 4mm single glazing. The glass maximises passive solar gain, reducing the need for heating during cold sunny days.

Maximising light while minimising heat gain

For orangeries and atria, solar control glass like Pilkington Suncool™ is becoming increasingly popular as it helps to create cooler, more comfortable spaces with less risk of overheating. Additionally, a high level of thermal insulation can be provided during the winter. 

If orangeries are being used to grow plants, fruit, or vegetables a balance between light and heat may be needed. Pilkington Suncool™ One 60/40 for example, only allows for 40 per cent of solar radiant heat transmittance, but 60 per cent of light transmittance in an IGU. 

Specifying glass with a low UV transmittance, such as Pilkington Optilam™, is desirable too, as excessive levels of UV radiation can be harmful to seedlings or younger indoor plants. However, some data suggests that the longer UV wavelengths can stimulate photosynthesis if visible light is also available.

How can plants flourish indoors?

Pilkington Spectrum can take out some of the guess work if a specific amount of light transmittance or heat insulation is required. You can use search parameters including U-value, g-value, light transmittance and both external and internal light reflectance, to help find products that match your requirements.

While it’s true that coated glass can influence the growth of indoor plants, there are tools available for fabricators to specify glazing that can provide the optimum conditions for healthy growth. 

Ultimately, glass with a neutral colour and high light transmittance should do the trick.

This feature was originally published in the May issue of Glass Times, and can be found here