{
  "id": 15954781,
  "title": "Invisible infrared light creates green letters that are less prone to blur",
  "url": "https://urgent.news/2026/10/21/invisible-infrared-light-creates-green-letters-that-are-less-prone-to",
  "topic": "science",
  "section": "Science",
  "published": "2026-10-21T21:20:21.000Z",
  "source": {
    "name": "Medical Xpress",
    "slug": "medical-xpress",
    "url": "https://medicalxpress.com/news/2026-10-invisible-infrared-green-letters-prone.html"
  },
  "original_language": "en",
  "account": "Scientists at the International Centre for Translational Eye Research (ICTER) have discovered that invisible near-infrared light can create green letters that are less prone to blur compared to conventional visible-light images. This phenomenon, known as two-photon vision, occurs when two photons are absorbed almost simultaneously, resulting in a combined energy close to that of a single photon at half the wavelength. As a result, near-infrared light with a wavelength around 1040 nm can produce a green light sensation similar to 520-nm green light.\n\nTo investigate the defocus tolerance of two-photon images, researchers conducted an experiment involving 12 healthy participants aged 25-47 with perfect or near-perfect vision. The participants' dominant eyes were tested, with one eye covered at a time, and no drugs were used to block the eye's natural accommodation process. The researchers used a scanning laser to display a small letter E, measuring the eye's amplitude of accommodation and the defocus tolerance for both two-photon and visible-light stimuli.\n\nThe main finding revealed that two-photon images tolerated greater defocus before participants perceived them as persistently blurred. The advantage persisted in both non-presbyopic and presbyopic groups, with the largest difference observed in the non-presbyopic group. Participants in this group reported the first signs of blur at a mean imposed defocus of 6.6 ± 0.7 diopters for the two-photon stimulus, compared to 4.3 ± 0.7 diopters for the visible-light stimulus. The range over which the two-photon image remained sharp was more than 1.4 times wider than the conventional visible-light image across all participants. This property is attributed to the quadratic dependence of two-photon absorption on local light intensity, which allows the edges of defocused beams to remain well defined at greater defocus.",
  "summary": "Infrared light is invisible to us. Yet under the right conditions, pulses of near-infrared light can give rise to a visible image in the eye—one that behaves in ways that defy intuition. ICTER scientists investigated what happens to that image when it is no longer perfectly focused.",
  "key_points": [],
  "editors_take": null,
  "illustration": null,
  "coverage": {
    "outlets": 1,
    "also_reported_by": []
  },
  "ai_generated": true,
  "disclaimer": "Summaries, key points and the editor’s take are written by software from other outlets’ reporting and may contain errors — always check the linked original."
}