Optics of sunlit water drops on leaves: Conditions under which sunburn is possible

Ádám Egri, Ákos Horváth, G. Kriska, Gábor Horváth

Research output: Contribution to journalArticle

6 Citations (Scopus)

Abstract

It is a widespread belief that plants must not be watered in the midday sunshine, because water drops adhering to leaves can cause leaf burn as a result of the intense focused sunlight. The problem of light focusing by water drops on plants has never been thoroughly investigated. Here, we conducted both computational and experimental studies of this phyto-optical phenomenon in order to clarify the specific environmental conditions under which sunlit water drops can cause leaf burn. We found that a spheroid drop at solar elevation angle θ ≈ 23°, corresponding to early morning or late afternoon, produces a maximum intensity of focused sunlight on the leaf outside the drop's imprint. Our experiments demonstrated that sunlit glass spheres placed on horizontal smooth Acer platanoides (maple) leaves can cause serious leaf burn on sunny summer days. By contrast, sunlit water drops, ranging from spheroid to flat lens-shaped, on horizontal hairless leaves of Ginkgo biloba and Acer platanoides did not cause burn damage. However, we showed that highly refractive spheroid water drops held 'in focus' by hydrophobic wax hairs on leaves of Salvinia natans (floating fern) can indeed cause sunburn because of the extremely high light intensity in the focal regions, and the loss of water cooling as a result of the lack of intimate contact between drops and the leaf tissue.

Original languageEnglish
Pages (from-to)979-987
Number of pages9
JournalNew Phytologist
Volume185
Issue number4
DOIs
Publication statusPublished - Mar 2010

Fingerprint

scald diseases
Sunburn
optics
Acer
Water
Sunlight
leaves
water
Acer platanoides
Optical Phenomena
solar radiation
Ferns
Light
Ginkgo biloba
Waxes
Salvinia natans
Salvinia
Hair
Lenses
Glass

Keywords

  • Environmental optics
  • Leaf burn
  • Phyto-optics
  • Plant leaf
  • Ray tracing
  • Solar radiation
  • Sunburn
  • Water drop

ASJC Scopus subject areas

  • Plant Science
  • Physiology

Cite this

Optics of sunlit water drops on leaves : Conditions under which sunburn is possible. / Egri, Ádám; Horváth, Ákos; Kriska, G.; Horváth, Gábor.

In: New Phytologist, Vol. 185, No. 4, 03.2010, p. 979-987.

Research output: Contribution to journalArticle

Egri, Ádám ; Horváth, Ákos ; Kriska, G. ; Horváth, Gábor. / Optics of sunlit water drops on leaves : Conditions under which sunburn is possible. In: New Phytologist. 2010 ; Vol. 185, No. 4. pp. 979-987.
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