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Title: next generation light sources and applications.

Abstract: The 4th generation light source has achieved tremendous success and leveraged scientific research in material science, biology and chemistry fundamentally. This paper discussed progress in LCLS as introduction and the possibility of accelerating driver beam with plasma wakefield in following section. Several potential applications of next generation light source are listed at the end.
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History of Light Sources

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  • First Online: 25 February 2017
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light source research paper

  • John F. Waymouth 5  

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There are many histories of discovery, invention, and development in the electric lamp industry. One of the best I have found, from the earliest days to 1947, is a book by Arthur Bright, “The Electric Lamp Industry” (Bright 1949 ). Several more recent ones are listed in the references (Zissis and Kitsinellis 2009 ; Gendre 2003 ). A Google TM search under the heading “History of Light Sources” turns up a number of websites, of which a sampling is listed ( ; ; ; ; ; ; ; ).

John F. Waymouth is retired.

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light source research paper


light source research paper

Energy Consumption and Environmental and Economic Impact of Lighting: The Current Situation

light source research paper

LEDs for photons, physiology and food


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John F. Waymouth

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Smart Lighting Engineering Center, Rensselaer Polytechnic Institute, Troy, New York, USA

Robert Karlicek

Department of Optics and Photonics, National Central University, Jhongli, Taiwan

Ching-Cherng Sun

Toulouse University, Toulouse, France

Georges Zissis

OLED Lighting, Universal Display Corporation, Ewing, USA

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Waymouth, J.F. (2017). History of Light Sources. In: Karlicek, R., Sun, CC., Zissis, G., Ma, R. (eds) Handbook of Advanced Lighting Technology. Springer, Cham.

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JSmol Viewer

Measuring system for determining the quality of led light sources and an overview of led light bulbs for household use.

light source research paper

1. Introduction

  • measurement and plot for observing fluctuations in the emitted luminous flux,
  • measurement and plot for observing the AC current flowing into the switching converter (LED bulb),
  • the illuminance measurement and polar diagram of the angular distribution of luminous intensity,
  • plotting the frequency spectrum and spectrogram of the luminous flux signal,
  • measurement of the luminous flux emitted by the light source.

2. Measuring System [ 7 ]

2.1. rotary sliding table with light bulb holder, 2.2. tunnel with apertures, 2.3. light bulb power cable stand, 2.4. chamber for preventing the influence of ambient light on measurements, 2.5. microcontroller and multifunctional measurement device red pitaya holder, 2.6. electronic assembly for stepper motor control, 2.7. electronic assembly for illuminance measurement, 2.8. system for high-frequency data acquisition.

  • sampling frequency: 300 kHz,
  • save measured samples in audio file format (WAV),
  • save samples from both analog inputs,
  • resolution of input channels: 16 bits,
  • data transmission protocol: TCP,
  • number of acquired samples: 150,000 (duration of the acquisition: 0.5 s),
  • IP address of the measurement device Red Pitaya.

2.9. Electronic Circuit for Observing Fluctuations in the Luminous Flux

2.10. electric circuit for measuring the electric current through a light bulb, 3. results and discussion, 3.1. list of measured led light bulbs, 3.2. classification of led light bulbs based on the percentage of fluctuations in the luminous flux, 3.3. classification of led light bulbs based on the percentage of deviation of the measured luminous flux value from the luminous flux value stated on the packaging, 4. conclusions, author contributions, institutional review board statement, informed consent statement, data availability statement, conflicts of interest.

  • Udovychenko, K.O. The Advantages and Disadvantages of Using Led Light Bulbs ; Tavria State Agrotechnological University: Melitopol, Ukraine, 2019; pp. 115–116. Available online: (accessed on 5 May 2021).
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  • Markovič, M. Measuring System for Determining the Quality of LED Substitutes for Conventional Light bulbs. Bachelor’s Thesis, University of Maribor, Maribor, Slovenia, 9 September 2021. [ Google Scholar ]
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  • Lock-in+PID, the Red Pitaya Board. Available online: (accessed on 25 June 2021).
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  • Bizjak, G.; Kobav, M.B.; Prelovšek, M. Razsvetljava , 1st ed.; Tomažič, S., Ed.; UL Fakuleta za Elektrotehniko: Ljubljana, Slovenia, 2014; Volume 390, pp. 63–65. Available online: (accessed on 19 August 2021).
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Click here to enlarge figure

Code nr.ManufacturerWattage [W]Luminous Flux [lm]Color Temperature [K]
1SYLVANIA (ToLEDo Retro GLS)78062700
2SYLVANIA (ToLEDo GLS)8.58062700
6EMOS (LED filament)810602700
7EMOS (LED A60, step dimmable)108802700
8EMOS (LED Classic)108062700
9OSRAM (LED value classic A60)8.58062700
10OSRAM (LED star classic A60, retrofit)78062700
12WELL LIGHT (Basic)107503000
13PHILIPS (CorePro LEDbulb)98062700
15OSRAM (LED superstar P25 advanced)42502700
16OSRAM (Parathom classic A100)1115212700
18HOMEWARE (LED filament)65502700
20V-TAC (LED A60 bulb)98064000
21V-TAC (Pro Samsung LED chip)98064000
22V-TAC (Dimmable filament A67 bulb)87002700
23V-TAC (LED R80 bulb)108004000
25ETA (LED filament)810552700
26TESLA (LED filament)44702700
27TESLA (reflektorska)75603000
29TUNGSRAM (LED filament)4.54702700
31BLAUPUNKT (G45 LED)44702700
32BLAUPUNKT (A60 LED)8.58063000
34GOOBAY (LED filament)44502700
36VOLTOLUX (LED filament)44702700
38SIMPEX (LED filament, dimmable)8.38062700
41S-BUDGET (LED filament)78062700
45KOBI-LIGHT (LED filament, retro)78002700
48GLOBO (LED filament)78062700
51ISKRA (LED filament)44002700
52EGLO (LED filament, dimmable)68062700
53GE LIGHTING (LED filament)55902700
54GE LIGHTING74702700
55BRILAGI (ECO line A60)109003000
56FARO (milky LED)78002700
58EGLO (dimmable)108063000
59PAULMANN (LED filament, dimmable)4.54702700
RankingCode nr.ManufacturerPercentage of Fluctuations [%]
1.8EMOS (LED Classic)0
2.27TESLA (reflektorska)4.1
3.23V-TAC (LED R80 bulb)5.0
5.16OSRAM (Parathom classic A100)7.6
7.13PHILIPS (CorePro LEDbulb)7.8
8.32BLAUPUNKT (A60 LED)8.3
11.7EMOS (LED A60, step dimmable)8.9
13.58EGLO (dimmable)10.8
15.55BRILAGI (ECO line A60)11.2
19.9OSRAM (LED value classic A60)12.8
RankingCode nr.ManufacturerDeviation [%]
1.16OSRAM (Parathom classic A100)−0.3
4.38SIMPEX (LED filament, dimmable)−1.0
6.34GOOBAY (LED filament)2.3
8.48GLOBO (LED filament)−3.3
9.21V-TAC (Pro Samsung LED chip)−3.3
13.32BLAUPUNKT (A60 LED)−5.1
16.23V-TAC (LED R80 bulb)−6.3
19.56FARO (milky LED)−7.2
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Markovič, M.; Orgulan, A.; Sukič, P. Measuring System for Determining the Quality of LED Light Sources and an Overview of LED Light Bulbs for Household Use. Sensors 2022 , 22 , 8351.

Markovič M, Orgulan A, Sukič P. Measuring System for Determining the Quality of LED Light Sources and an Overview of LED Light Bulbs for Household Use. Sensors . 2022; 22(21):8351.

Markovič, Matic, Andrej Orgulan, and Primož Sukič. 2022. "Measuring System for Determining the Quality of LED Light Sources and an Overview of LED Light Bulbs for Household Use" Sensors 22, no. 21: 8351.

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Physical Review Letters

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Brighter Light Sources from Black Metal: Significant Increase in Emission Efficiency of Incandescent Light Sources

A. y. vorobyev, v. s. makin, and chunlei guo, phys. rev. lett. 102 , 234301 – published 10 june 2009.

  • Citing Articles (170)

By applying the femtosecond laser blackening technique directly to a tungsten incandescent lamp filament, we dramatically brighten the tungsten lamp and enhance its emission efficiency to approach 100%. A comparison study of emission and absorption for the structured metal surfaces shows that Kirchhoff’s law is applicable for the black metal. Furthermore, we demonstrate that we can even obtain partially polarized light as well as control the spectral range of the optimal light emission from the laser-blackened tungsten lamp.


  • Received 1 August 2008


©2009 American Physical Society

Authors & Affiliations

  • 1 The Institute of Optics, University of Rochester, Rochester, New York 14627, USA
  • 2 The Research Institute for Complex Testing of Optoelectronic Devices, City of Sosnovy Bor, Leningrad District, 188540, Russia
  • * Corresponding author; [email protected]

Comments & Replies

Comment on “brighter light sources from black metal: significant increase in emission efficiency of incandescent light sources”, k. c. mishra, m. zachau, and r. e. levin, phys. rev. lett. 103 , 269401 (2009), phys. rev. lett. 106 , 249401 (2011), vorobyev, makin, and guo reply:, phys. rev. lett. 106 , 249402 (2011), phys. rev. lett. 103 , 269402 (2009), article text (subscription required), references (subscription required).

Vol. 102, Iss. 23 — 12 June 2009

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  • v.30(2); 2016 Feb

What is light? The visible spectrum and beyond

1 Department of Environmental Health Sciences, The Johns Hopkins University School of Public Health, Baltimore, MD, USA

In this International Year of Light, it is particularly appropriate to review the historical concept of what is light and the controversies surrounding the extent of the visible spectrum. Today we recognize that light possesses both a wave and particle nature. It is also clear that the limits of visibility really extend from about 310 nm in the ultraviolet (in youth) to about 1100 nm in the near-infrared, but depend very much on the radiance, that is, ‘brightness' of the light source. The spectral content of artificial lighting are undergoing very significant changes in our lifetime, and the full biological implications of the spectral content of newer lighting technologies remain to be fully explored.

Introduction—Defining Light

The typical dictionary definitions of ‘light' (noun) are: ‘The natural agent that stimulates sight and makes things visible; also, a source of illumination, especially an electric lamp.' Finally, ‘a device that makes something start burning, as a match, lighter, or flame.' However, the more technical, scientific definition can be obtained from the ‘International Lighting Vocabulary (ILV) published by the International Commission on Illumination (the CIE). The definition found in the ILV has a number (#17–659) and reads:


1. characteristic of all sensations and perceptions that is specific to vision ;

2. radiation that is considered from the point of view of its ability to excite the human visual system.'

The CIE provides two interesting notes to this formal definition of light: ‘NOTE 1—This term has 2 meanings that should be clearly distinguished. When necessary to avoid confusion between these 2 meanings the term ‘ perceived light ' may be used in the first sense' and ‘NOTE 2—Light is normally, but not always, perceived as a result of the action of a light stimulus on the visual system .' [This latter note was added even before the photoreceptive retinal–ganglion cells (pRGCs) were known, and of course the pRGCs also influence vision when controlling pupil size and lid position 1 and may even have a type of retinal image role in vestibular function. 2

Background—Sources of Light

Although ‘light' refers to visible radiant energy, it may refer to sources of illumination, such as sunlight or artificial sources such as a lamp and luminaires (ie, lamp fixtures). One might think of sunsets or even the nighttime sky! Throughout almost all of humankind's evolution, there was only natural sunlight—or fire (including, candles, flame torches, and later oil lamps). But today—and over the past century—electrically powered lamps have dominated our nighttime environments in the developed countries. Since the 1820s-1830s gas lamps and (later) incandescent (red-rich) lamps have dominated our indoor environment at night. Open flames and incandescent sources are described technically as having low-color temperatures, typically ⩽2800 Kelvins (K)—rich in longer visible (orange, red) wavelengths and infrared–near-infrared radiation. By contrast, the midday Sun is rich in shorter wavelengths with a color temperature of about 6500 K. Sunlight become red-rich when low in the sky and the significant change in spectrum is often unnoticed because of selective chromatic adaptation by our visual system.

Since the 1950s, fluorescent lamps (generally rich in green light and line spectra) have been widely used in indoor lit environments, at least in office and commercial settings, but rather infrequently in the home—with perhaps one exception—in the kitchen (USA experience). But the ‘revolution' in optics during the 1960s—fostered largely by the invention of the laser—led to other optical technologies, including the development of new types of lenses and filters, holography, and light-emitting diodes (LEDs). LEDs were far more energy efficient than incandescent sources but initially were capable of emitting only very narrow wavelength bands, that is, single-color visible LEDs, until the invention of multi-chip LEDs and blue–violet-pumped-fluorescent LEDs to produce ‘white' light.

In this century, governmental emphasis on energy conservation led to pressure to employ compact fluorescent lamps (CFLs) and ‘white' LEDs for illumination. Solid-state lighting by LEDs, which are even more energy efficient than CFLs, are now beginning to dominate the marketplace. However, both the early CFLs and ‘white' LEDs have very blue-rich spectral power distributions ( Figure 1 ). Some consumers began to rebel with such blue-rich lamps and demanded less ‘harsh,' less ‘cold-bluish' light sources. You will now find some LEDs and CFLs with greatly reduced blue emission. Nevertheless, in the past 60 years there has been an ever-increasing color temperature of artificial sources and an increase in nighttime ‘light pollution.' The night sky of Western Europe as seen from space shows the enormous impact of electric lighting ( Figure 2 ).

An external file that holds a picture, illustration, etc.
Object name is eye2015252f1.jpg

Relative spectral power distributions. Traditional tungsten lamps (······) had little shortwavelength light emission compared with ‘white' fluorescent (–––) and LED (——) lamps. Most white LEDs have an absence of deep red and near-infrared emissions.

An external file that holds a picture, illustration, etc.
Object name is eye2015252f2.jpg

The nighttime lights of Western Europe can be seen from outer space, showing the enormous impact of artificial lighting on the night sky (from NASA).

Atmospheric optics significantly alters sunlight and sometimes provides wonderful displays of color, including the Green Flash (a great rarity)! The atmosphere acts like a mild prism: the refractive index varies slightly with wavelength, exaggerating the Sun's image low on the horizon. Different colors are bent to different amounts by the atmosphere and the Sun's image is bent ~0.6° at the horizon so that the Sun actually sets before its refracted image sets! The red image sets first, followed by green which is seen for only a fraction of second and blue light does not appear because it has been scattered out. 3

Historical views

Since primitive times, humans have wondered just ‘What is light?' Biblically ( King James ‘Authorized Version', Cambridge Edition )—Genesis 1 : 3 (Day 4) reads: ‘And God said, Let there be light: and there was light.' Many great minds developed theories of light ( Figure 3 ). Classical Greek thinking on ‘ What is light ?' led Plato (428–328 BC) to the theory that light originated as ‘feeling rays' from the eyes—directed at whatever one observes. He apparently drew on the fact that light is produced within the eye by pressure phosphenes. Although today this notion seems strange, this description dominated Western thought for nearly two millennia. In the seventeenth century a controversy arose as to whether light was a wave or a stream of particles. Sir Isaac Newton argued here in Cambridge that Grimaldi's diffraction phenomena simply demonstrated a new form of refraction. Newton argued that the geometric nature of the laws of refraction and reflection could only be explained if light were composed of ‘corpuscles' (particles), as waves did not travel in straight lines. After joining the Royal Society of London in 1672, Newton stated that the forty-fourth of a series of experiments he had just conducted had proven that light consisted of corpuscles—not waves. However, on the continent the wave theory of light appeared to hold sway. Christiaan Huygens, a Dutch physicist (physics in that century was termed ‘natural philosophy') published his Traité de la Lumière in 1690 which supported the wave theory. Not until Sir Thomas Young clearly demonstrated wave interference ( Experiments and Calculations Relative to Physical Optics , 1804) 4 was the wave theory fully accepted—and the wave theory held sway at least until the end of the nineteenth century. Another prominent physicist at Cambridge was James Clerk Maxwell who in the mid-nineteenth century derived his universal rules of electricity and magnetism that predicted electromagnetic waves and the electromagnetic spectrum ( Figure 4 ). Indeed, around 1800 the existence of ultraviolet and infrared radiation had been discovered by Ritter 5 and Herschel, 6 respectively.

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Many great minds have theorized on the nature of light from Plato to Maxwell and Einstein. Of course, Einstein need not be shown as his image is universally known.

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Electromagnetic waves and the electromagnetic (E–M) spectrum. (a) (top) A geometrical representation of an oscillating E–M wave with E (electric) and H (magnetic) fields. (b) (below) Familiar regions of the E–M spectrum.

At the turn of the nineteenth century (1899–1901), a crisis developed in classical physics. Physicists had to deal with a very big puzzle: In some experiments such as interference and diffraction, light behaved as waves. However, in other experiments, such as the photoelectric effect, light appeared to behave as if particles. The photoelectric effect was observed in some metals when exposed to a beam of light. But only shorter wavelengths would produce a photocurrent in the metal, whereas longer wavelength (red) light—even at high intensity—would not produce a photocurrent. This curious observation strongly supported the quantum theory of radiation. Some German physicists theorized that a single photon (particle of light) has a quantum energy Q ν that is directly proportional to the frequency f (sometimes symbolized by the Greek letter, ν ) of the wave:

Q ν = h × f ,

where h is known as ‘Planck's Constant.' This led to the concept of ‘wave–particle duality.'

Physicists eventually reached a consensus that light could be characterized simultaneously as both a stream of particles and a wave. Some aspects of quantum theory are quite strange, and we shall not delve deeper, but even Einstein had problems with accepting quantum theory. But then it was Einstein who theorized that the speed of light in a vacuum could not be exceeded—and also (in 1916) predicted ‘stimulated emission of radiation,' which was the theoretical basis for the laser. 7

Most people know that the velocity of light is a constant—about 300 000 km/s in a vacuum but 299 000 km/s in air and slows down even more in denser media, for example, ~225 000 km/s inside the eye. The ratio of the speed of light in a vacuum to that in a medium is the ‘index of refraction, n .' Just a few months ago, a team at the Ecole Politechnique Lausanne alleged that they had produced the first photograph of light particles and waves! I am not sure that I understood their experimental technique, but it will be interesting to see if other laboratories can reproduce their results and confirm their interpretation of their images. Figure 5 provides a scale for comparing the dimension of one wavelength of light.

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Wavelength as a matter of scale. A single retinal melanin granule or red blood cell has dimensions of the order of one wavelength from a neodymium laser (1.064  μ m=1064 nm).

Quantum theory and stimulated emission

At the atomic scale, photons are emitted when an electron jumps to a lower energy orbital of the atom. Stimulated emission of a photon can occur only if an initial photon of the exact energy passes by an excited atom. Atoms are generally excited by a photon being absorbed and raising the atom to a higher energy level followed by a photon spontaneously emitted as the atom drops to a lower energy level, except by stimulated emission. With a properly constructed resonant cavity, a cascade of stimulated emissions can occur with a resulting laser beam. The real benefit of a laser source is its ultra-high radiance (brightness). Virtually all applications of a laser—from laser pointers, laser rangefinders, and CD writing and reading to laser fusion—are only possible because of the ultra-high radiance of a laser. A 1-mW laser pointer has a brightness (radiance) at least 10 times greater than the Sun.

What are the limits of the visible spectrum?

There really are no agreed limits to the visible spectrum. The CIE defines ‘visible radiation (ILV term number 17–1402) as ‘any optical radiation capable of causing a visual sensation directly'. The CIE definition adds the following note that ‘There are no precise limits for the spectral range of visible radiation since they depend upon the amount of radiant power reaching the retina and the responsivity of the observer. The lower limit is generally taken between 360 and 400 nm and the upper limit between 760 and 830 nm'. The limits of visibility have long been a personal interest. As a young scientist of about 24 years of age, I performed an experiment to determine the shortest wavelength that that I could see after reviewing much earlier reports on the subject. 8 , 9 , 10 I could image the slit of a double monochromator down to 310 nm, and I was certain that I was truly imaging 310 nm and not stray light of longer wavelengths as I placed a number of spectral filters in the beam with no change in detection threshold. But today, at age 74, I cannot even see 400 nm very easily! As I have aged, the buildup of UV-absorbing proteins—many are fluorophores—in my intact crystalline lenses block most UV-A (315–400 nm) wavelengths and I experience more haze from lens fluorescence than when younger. Everyone can experience lens fluorescence 11 from the UV-A (315–400 nm), and Zuclich et al 12 quantified UV-A lens fluorescence and how it varies little with age. Weale 13 estimated that lens fluorescence interfered with visual performance. Insects are quite sensitive to UV and this is the basis of UV insect light traps. Bees are believed to make use of the polarized UV in skylight to navigate, but humans presumably do not knowingly make use of the polarized violet sky, despite some polarizing features of the human cornea producing Haidinger Brushes. 14 During World War II, concerns arose that preexposure to ultraviolet decreased night vision, 15 but even the renowned vision scientist, George Wald, argued with a University of Rochester graduate student that this finding was ridiculous as the crystalline lens blocked retinal UV-A exposure. Apparently Professor Wald did not think logarithmically in this case, as nearly 1% of UV-A is transmitted, and with higher photon energies from the shorter UV wavelengths, it was not implausible that UV-A radiation could affect rod photoreceptors. 16 There was a small tempest that continued with Wolf 17 confirming the decrease in night vision, but even later, Wald 18 argued this was neither a significant nor permanent effect. Tan 19 later measured the grayish vision in aphakic individuals that confirmed the secondary UV-A response peaks of each cone photoreceptor.

Seeing infrared ‘light'

After several curious stories about soldiers seeing infrared lasers in the 1970s, my group demonstrated visual detection to nearly 1100 nm ( J Opt Soc Amer 1976). Figure 6 shows the extension of the spectral responsivity of vision well into the infrared. This was not an easy experiment. We separated the laser by 8 m from the observer to reduce pump light (pump light rapidly decreased with distance but the laser-beam irradiance did not), and we employed narrow-band infrared filters, stacked until the same threshold was measured without the addition of another filter ( Figure 7 ). It was interesting that—similar to other visible wavelengths—color identification was difficult at threshold for a point source, 20 but if we exceeded threshold and, particularly, if expanded the source size from a ‘point', we always could see red, suggesting that the red cones were activated. Additionally, we conducted experiments that confirmed reports from field night observations that one would see ‘green' light from within the beam of a short-pulsed Nd:YAG laser at several kilometers down-range. We were able to confirm that if one directly observed the 1064-nm near-infrared emission wavelength from a q -switched (~10–20 ns) Nd:YAG laser one would observe green light, which when color-matched with a CW monochromator source, appeared as 532-nm green light. This demonstrated to us that second-harmonic generation was occurring within ocular tissues—probably at the retina. A second harmonic was not seen in the ruby (694 nm) laser, demonstrating the low efficiency of this non-linear process.

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Photopic spectral sensitivity of the human eye V ( λ ) extended into the infrared (after Sliney et al 25 ). The circles are larger than the SD of measured thresholds for detecting a point source.

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Experimental arrangement used in 1970 experiments of infrared visual sensitivity (Sliney et al 25 ).

In a paper published last December, Palczewska et al 21 argued that infrared vision is the result of two-photon isomerization; however, as they employed only trains of femtosecond (10 −12  s) pulses from an infrared laser, they could not rule out non-linear processes. Their experiments were good, but in my view, their interpretations appear flawed, as they ignored the impact of their laser's peak power of 67 000 above average. They could not assume that their 200-fs, 75-MHz laser was equivalent to a continuous source (with duty cycle of only 1.5 × 10 −5 ), so non-linear effects were not surprising. Their 1-mW average power entering the eye actually had a peak power of 66 W, producing a retinal irradiance >13 MW/cm 2 in a minimal retinal spot size of ~25 μm!

We can conclude that visibility of light outside the well-accepted range of about 380–780 nm depends upon the brightness (radiance) of the source but is limited in childhood to approximately 310 nm at the short wavelength of the visible spectrum to perhaps ~1100 nm in the near-infrared. A true dividing line simply does not exist between ‘visible' and infrared. The visibility of an infrared A (IR-A) wavelength merely depends only on the brightness (radiance) of the source compared with ambient luminance.

CIE photobiological spectral bands

The CIE developed some useful short-hand notations for photobiology in the 1930s. These were: the UV-C from 100–280 nm (highly actinic; germicidal, with a short-wavelength border with the ‘soft-X-ray' region), the UV-B between 280 and 315 nm with actinic and photocarcinogenic effects, and the UV-A between 315 and 400 nm, which is characterized as weakly actinic and has a major role in photodynamic effects and photosensitizers. The visible spectrum intentionally overlaps the UV-A (from ~360–380 to 400 nm in the deep violet) and well into the near-infrared (IR-A) spectral band, which begins at 780 nm. To some surprise for research photobiologists, the borders of these CIE spectral bands have sometimes created controversy in the industrial sector. There is actually a rather infamous ‘standard' published by the International Standards Organization (ISO) that attempted to change the traditional CIE definitions of UV-A that had existed for >75 years (ISO-20473–2007). The ISO technical committee, TC172 (optics), prepared this spectral band standard by redefining UV-A to <380 nm rather than the CIE 400-nm definition and attempted to suggest a fine border between visible—beginning at 380 nm. 22 Key ophthalmic industry members of the Committee favored ophthalmic lenses and sunglasses that could meet much more lenient criteria for ‘UV blocking!'

The CIE identifies three infrared spectral bands—based largely on spectral variations in the absorption of infrared by water. The IR-A ranges from 780 to 1400 nm (metavisible wavelengths), which are well transmitted by water and which reach the retina through the ocular media. As noted earlier, a very weak visual stimulus exists even at 1100 nm; and IR-A is deeply penetrating into biological tissues and thus used in diagnostics and in skin treatments. The infrared B ranges between 1.4  μ m (1400 nm) and 3.0  μ m (middle infrared), and these wavelengths do not reach the retina but penetrate as much as a few mm into the skin and ocular tissues. The infrared C is a vast spectral domain, extending from 3.0 to 1000  μ m (1 mm). These far-infrared wavelengths are absorbed very superficially (<1 mm). The extreme infrared C is also referred to as terahertz (THz) radiation.

Measuring light—the CIE standardized radiometric and photometric terms

The CIE defines two separate systems for measuring light: the photometric and the radiometric systems. The radiometric system is based upon fundamental physical units ( Table 1 ). The photometric system is used in lighting design and illumination engineering and is based upon an approximate, but standardized, ( V ( λ )) spectral response of daylight (photopic) vision with units of: lumens (luminous power Φ v ), lux (lm/m 2 for illuminance E v ), candelas (lm/sr for luminous intensity I v ), and nits (cd/m 2 for luminance L v , ie, ‘brightness'). The radiometric system is employed by physicists to quantify radiant energy independent of wavelength; whereas photometric quantities are only used for visible light, but radiometric quantities and units apply in the ultraviolet and infrared spectral regions as well. 23 Detailed terms, quantities, and units are provided online in the CIE electronic ILV at , and these are used widely in international (ISO and IEC) standards.

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Calculating retinal exposures

The retinal irradiance E r is directly proportional to the radiance (brightness) L of the source being viewed. The retinal irradiance E r in W/cm 2 is:

E r =0.27 × L × τ × d e 2

where L is the radiance in W/cm 2 /sr, τ is the transmittance of the ocular media and d e is the pupil diameter in cm. Two persons looking at the same scene can easily have a pupil size sufficiently different to readily have a retinal irradiance differing by a factor of 2 (100%)!

The retinal illuminance (photometric measure) is measured in Trolands (td) and is the luminance L (cd/m 2 ) of the source viewed, multiplied by the square of the pupil diameter (in mm). This unit has been widely used in studies of ‘flash blindness' and some areas of vision research. The retinal irradiance from ambient outdoor illumination is of the order of 0.02–0.1 mW/cm 2 and these levels are just comfortable to view. The retinal illuminance outdoors is ~5 × 10 4  td. Directly viewing the midday sun's image—a million-fold greater radiance than the blue sky or most of the outdoor surround—can result in a retinal irradiance of ~6 W/cm 2 or ~3 × 10 7  Td for a 1.6-mm pupil. Flashblindness studies normally cite ~10 7  Td × s as a ‘full bleach', which would occur in one-third second.

It is hard to predict future developments in our understanding and use of light; hopefully not more blue light at night. Our understanding of the multiple roles of pRGCs has only begun. Although incorrectly labeled by some as ‘non-visual photoreceptors', they have important roles with other photoreceptors in pupillary constriction (improving visual acuity and depth of focus) and upper-lid position to reduce sky glare and shield the inferior retina in bright daylight. 1 There is also evidence that pRGCs have some direct roles in imaging. 2 We know little about what occurs if overdriven. 24

The author declares no conflict of interest.

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  • Published: 08 July 2024

Fast free-electron laser targets the future

  • David Pile 1  

Nature Photonics volume  18 ,  pages 640–642 ( 2024 ) Cite this article

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  • Free-electron lasers
  • Lasers, LEDs and light sources
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Following first lasing at LCLS-II — a coherent X-ray laser source driven by a 700-m superconducting linear accelerator — several upgrades are already in the works. Nature Photonics spoke to LCLS director Mike Dunne about LCLS-II commissioning hurdles as well as future plans.

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July 13 – 19, 2024  |  No. 508

Almost two decades after winning the Prime Minister’s Prize for Science, a University of Queensland professor’s pioneering research into honey bee navigation has been called into question. By Jackson Ryan .

Questions over australia's leading honey bee research.

Professor Mandyam Veerambudi Srinivasan studying bees in 2006.

Watch a honey bee return to its hive after foraging and you may witness a curious dance. Homecoming bees rapidly move in a figure-eight motion and then shake their abdomens. About 2300 years ago Aristotle witnessed the dance, suggesting it might be workers offloading pollen. In the 1920s, Austrian scientist Karl von Frisch decoded the dance: it was a form of communication.

He dubbed it Tanzsprache, “dance language”, and showed it was a way for bees to signal to hive mates the direction and distance to a food source. But how could these insects, with simple nervous systems, estimate how far away a flower lay? How did they know in which direction to take flight?

In the early 1990s, Mandyam Veerambudi Srinivasan, a researcher at Australian National University, answered that question. In an elegant series of experiments using patterned tunnels, he led work that calibrated the “honeybee odometer”, showing bees measure distance by determining how quickly the world blurs past their eyes during flight.

The work made Srinivasan a star. In 2001 he was elected a fellow of London’s prestigious Royal Society and by 2006 he’d earnt the Prime Minister’s Prize for Science. Since 2001, Srinivasan has been listed as a chief investigator on Australian Research Council (ARC) funding totalling more than $30 million. Today, he is retired and holds an emeritus professorship at the University of Queensland.

A cloud has formed over his seminal studies, however. In May, two researchers from the California Institute of Technology (Caltech), Laura Luebbert and Lior Pachter, uploaded a manuscript to the website, a repository for scientific articles yet to be peer reviewed or published. In it, they claimed that 10 papers underpinning honey bee odometry contained “inconsistencies in results, duplicated figures, indications of data manipulation, and incorrect calculations”. Srinivasan is listed as an author, or co-author, on all of them.

“I can categorically confirm that the data was not cleaned up or manipulated in any way,” Srinivasan tells The Saturday Paper .

Luebbert and Pachter believe the errors are a potential sign of misconduct. “I don’t know what there is to debate or discuss or defend, unless the author can produce the notebooks and show exactly what happened and explain why this happened, which he already said he cannot,” Pachter says.

Australia does not have a national, independent research integrity body to investigate claims of scientific misconduct. Instead, universities are tasked with investigating researchers within their institutions, presenting potential conflicts of interest. These investigations remain confidential and participants are often required to sign non-disclosure agreements, which makes it difficult to track the extent of research integrity complaints in Australia.

The University of Queensland, where Srinivasan is an emeritus professor, said it forwarded details of the concerns to Australian National University, where the research in question was conducted. A spokesperson for ANU first told The Saturday Paper it had not received any formal complaints about the work, before clarifying it had received “a referral from the University of Queensland”.

Srinivasan is preparing a response to the claims and plans on submitting it to arXiv. In a draft copy of the response, seen by The Saturday Paper , he states the claims “are totally unfounded and the suggestions and allegations by Luebbert and Pachter as to how data manipulation might have been achieved are not only totally puzzling, but deeply concerning”.

Srinivasan remains a chief investigator on one ARC grant, worth $444,293. He says he receives no money from the grant; his major contribution is helping with data analysis and manuscript writing. Matt Garratt, a professor at the UNSW AI Institute and also a chief investigator on the ARC grant, tells The Saturday Paper: “I have the utmost respect for Srini and can only attest in the work we have done together, he has been very rigorous to ensure all results are properly reported and presented.”

Luebbert says she first noted the alleged inconsistencies in the honey bee papers four years ago. In early 2020, as a first-year PhD student, she was trying to work out where her postgraduate studies would take her. The pandemic cruelled her plans but journal clubs – where researchers review papers and give short presentations to lab mates – provided a way to experience many different research fields.

During a stint in a lab studying insect locomotion, she was tasked with reviewing two papers on how honey bees navigate the world. One, published in the prestigious journal Science in 2000, contained a calculation that Luebbert just couldn’t understand. A single number stood out: 17.7. It didn’t match the observations in the paper. “I had absolutely no idea what it meant,” Luebbert says. “I tried to gain an understanding by reproducing their analysis … and I just kept getting a different number.”

In another paper, published in the Journal of Experimental Biology (JEB) , she found graphs that were identical. The graphs appeared to have been reused but claimed to show results from separate experiments with different set-ups. Luebbert was both excited and concerned about bringing the findings to the journal club. On April 9, 2020, she gave her presentation.

The findings were met with “little more than a collective shrug” – even a tenured professor appeared uninterested in the potential integrity issues. Dejected, she decided to drop it. “I honestly had kind of given up hope,” she says.

Nevertheless, she raised her concerns on PubPeer, a website that allows researchers and the public to comment on peer-reviewed publications after they’ve been published – an online version of journal club. Luebbert placed her commentary on one of the papers in JEB , pointing out the graph duplications.

She turned her focus to her studies but the collective shrug was something she never forgot. When she began to work in Pachter’s lab, the pair eventually took up the cause again, finding what they believed to be further issues in the honey bee work. They published on arXiv in May and then wrote a lengthy blog post detailing some of the allegations they were making on July 2.

Of the more serious claims, Luebbert and Pachter suggest data has been “seemingly manipulated” across six papers. In their manuscript, they highlight the previously mentioned JEB papers from 1996 and 1997, and four others.

In one, published in the journal Biological Cybernetics in 2000, the Caltech duo say data had been reused from the 1996 JEB paper, and they said a 2004 paper reused “problematic data” from the former. Srinivasan again pointed to these errors being typographical.

On June 25, the two papers published in JEB , in 1996 and 1997, received “expressions of concern” – an editorial note to alert readers of potential issues. Srinivasan says he was contacted by the journal “about a year ago” and explained to it how the errors were made. He also says he takes full responsibility for them, and the data underlying the experiments, which are almost 30 years old, no longer exists.

However, he says he never heard directly from Luebbert or Pachter. “They didn’t have the courtesy to even contact me about this for any clarification before they put the thing up on arXiv.” PubPeer is designed to automatically email authors of papers with new comments, but Srinivasan maintains he was never contacted by the website’s publishers.

The expressions-of-concern notices on the JEB papers did not appease Luebbert or Pachter. “We were really not happy with them,” Luebbert says. “They completely dismissed these instances of data duplication in their two papers.”

Craig Franklin, who serves as editor-in-chief of JEB , tells The Saturday Paper the issues were investigated, alongside “an expert working in this field” and that resulted in the expressions of concern. “If additional concerns are raised, we will investigate further,” he says.

The Caltech pair do not believe the expressions of concern go far enough, nor capture the scope of the issues they’ve raised across many different papers. “I feel like given such a major discrepancy, or like a mess up like this … there’s no choice but to retract the paper,” Pachter says.

Other researchers who’ve read the Luebbert and Pachter manuscript say it would be worthwhile for journals to investigate the claims. “All in all there is enough there to look at it more closely, but I am also not immediately convinced that widespread misconduct happened,” says Roger Schürch, an assistant professor of entomology at Virginia Tech.

Srinivasan disagrees. “The results are completely solid, so I don’t see any reason to retract these papers,” he says.

This article was first published in the print edition of The Saturday Paper on July 13, 2024 as "Fight of the honey bee".

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July 13 – 19, 2024 Edition No. 508

‘A little more adventurous’: Inside Dutton’s youth crime strategy Jason Koutsoukis

Women call for action as reports of financial abuse surge Karen Barlow

The state of Australia’s economic mobility Danielle Wood

Bird flu threatens Philip Island’s penguin colony Kate Holden

Should Australia's corporate watchdog be dismantled? Mike Seccombe

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Questions over Australia's leading honey bee research Jackson Ryan

France faces political gridlock despite far-right’s poll defeat Jonathan Pearlman

Understanding Xi Jinping Stan Grant

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Labor and the Muslim vote Paul Bongiorno

Australia needs a working corporate watchdog John Hewson

Jon Kudelka cartoon, July 13, 2024 Jon Kudelka

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Ingmar Bergman at the Scandinavian Film Festival Christos Tsiolkas

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The start of something Elisabeth Knowles

Only the Astronauts Miriam Cosic

The Mires James Bradley

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Kangaroo tail in brik pastry David Moyle

Landlordism in the ‘lucky country’ Elizabeth Farrelly

Australia’s Rachel Gunn on breakdancing at the 2024 Olympics Martin McKenzie-Murray

Cryptic Crossword No. 508 Liam Runnalls

How many AFL clubs have birds as their mascots? Cindy MacDonald

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