A report on Light and Radiometry

A triangular prism dispersing a beam of white light. The longer wavelengths (red) and the shorter wavelengths (blue) are separated.

The electromagnetic spectrum, with the visible portion highlighted

Beam of sun light inside the cavity of Rocca ill'Abissu at Fondachelli-Fantina, Sicily

$Due to refraction, the straw dipped in water appears bent and the ruler scale compressed when viewed from a shallow angle.$

Hong Kong illuminated by colourful artificial lighting.

$Thomas Young's sketch of a double-slit experiment showing diffraction. Young's experiments supported the theory that light consists of waves.$

Radiometry is a set of techniques for measuring electromagnetic radiation, including visible light.

- Radiometry

Light is measured with two main alternative sets of units: radiometry consists of measurements of light power at all wavelengths, while photometry measures light with wavelength weighted with respect to a standardized model of human brightness perception.

- Light

2 related topics with Alpha

Photopic (daytime-adapted, black curve) and scotopic (darkness-adapted, green curve) luminosity functions. The photopic includes the CIE 1931 standard (solid), the Judd-Vos 1978 modified data (dashed), and the Sharpe, Stockman, Jagla & Jägle 2005 data (dotted). The horizontal axis is wavelength in nm.

Photometry (optics)

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Photometry is the science of the measurement of light, in terms of its perceived brightness to the human eye.

It is distinct from radiometry, which is the science of measurement of radiant energy (including light) in terms of absolute power.

Optics

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Alhazen (Ibn al-Haytham), "the father of Optics"

$Reproduction of a page of Ibn Sahl's manuscript showing his knowledge of the law of refraction.$

The first treatise about optics by Johannes Kepler, Ad Vitellionem paralipomena quibus astronomiae pars optica traditur (1604)

Cover of the first edition of Newton's Opticks (1704)

$Geometry of reflection and refraction of light rays$

Illustration of Snell's Law for the case n1 < n2, such as air/water interface

A ray tracing diagram for a converging lens.

Images of black letters in a thin convex lens of focal length f are shown in red. Selected rays are shown for letters E, I and K in blue, green and orange, respectively. Note that E (at 2f) has an equal-size, real and inverted image; I (at f) has its image at infinity; and K (at f/2) has a double-size, virtual and upright image.

When oil or fuel is spilled, colourful patterns are formed by thin-film interference.

Conceptual animation of light dispersion through a prism. High frequency (blue) light is deflected the most, and low frequency (red) the least.

Dispersion: two sinusoids propagating at different speeds make a moving interference pattern. The red dot moves with the phase velocity, and the green dots propagate with the group velocity. In this case, the phase velocity is twice the group velocity. The red dot overtakes two green dots, when moving from the left to the right of the figure. In effect, the individual waves (which travel with the phase velocity) escape from the wave packet (which travels with the group velocity).

A polariser changing the orientation of linearly polarised light. In this picture, θ1 – θ0 = θi.

The effects of a polarising filter on the sky in a photograph. Left picture is taken without polariser. For the right picture, filter was adjusted to eliminate certain polarizations of the scattered blue light from the sky.

Experiments such as this one with high-power lasers are part of the modern optics research.

Model of a human eye. Features mentioned in this article are 1. vitreous humour 3. ciliary muscle, 6. pupil, 7. anterior chamber, 8. cornea, 10. lens cortex, 22. optic nerve, 26. fovea, 30. retina

The Ponzo Illusion relies on the fact that parallel lines appear to converge as they approach infinity.

Illustrations of various optical instruments from the 1728 Cyclopaedia

A colourful sky is often due to scattering of light off particulates and pollution, as in this photograph of a sunset during the October 2007 California wildfires.

Optics is the branch of physics that studies the behaviour and properties of light, including its interactions with matter and the construction of instruments that use or detect it.

Other research focuses on the phenomenology of electromagnetic waves as in singular optics, non-imaging optics, non-linear optics, statistical optics, and radiometry.