question: Why are blue coloured lights so hard to see and read?
comment: There might be other effects in play as well, but the human eye is least sensitive to blue and violet colors compared to others. For two lights of equivalent energy, the bluer one will appear significantly dimmer than another color.
passages: Humans cannot see ultraviolet light directly because the lens of the eye blocks most light in the wavelength range of 300–400 nm; shorter wavelengths are blocked by the cornea. The photoreceptor cells of the retina are sensitive to near ultraviolet light, and people lacking a lens (a condition known as aphakia) see near ultraviolet light (down to 300 nm) as whitish blue, or for some wavelengths, whitish violet, probably because all three types of cones are roughly equally sensitive to ultraviolet light; however, blue cone cells are slightly more sensitive.
   Section::::Background.
  
  Blue light is a range of the visible light spectrum, defined as having a wavelength between 400−495 nm. This short wavelength means that blue light is a type of high-energy visible light, defined as having a wavelength between 400 and 450 nm.
   Although rg chromaticity contains less information than RGB or HSV color spaces, it has a number of useful properties for computer vision applications. Notably, where a scene viewed by a camera is not lit evenly – for example if lit by a spotlight – then an object of a given color will change in apparent color as it moves across the scene. Where color is being used to track an object in an RGB image, this can cause problems. The lack of intensity information in rg chromaticity images removes this problem, and the apparent color remains constant. Note that in the case where different parts of the image are lit by different colored light sources, problems can still emerge.
   Section::::Challenges.
  
  One problem that currently hampers the widespread adoption of this highly energy efficient technology is that the average lifetimes of red and green PHOLEDs are often tens of thousands of hours longer than those of blue PHOLEDs. This may cause displays to become visually distorted much sooner than would be acceptable for a commercially viable device.
   Light is transmitted to the retina through the lens. In humans, the amount of light transmitted by the lens is age-dependent. In young children, more than 65% of blue light is transmitted. This transmission rate decreases over time; at age 25, only 20% of blue light is transmitted to the retina. The decreased transmission of blue light occurs as our eyes’ lens naturally yellows and absorbs more blue light over time, thus preventing blue light from reaching the retina. As a result of this natural process, younger people are more susceptible to the effects of blue light.
   Electromagnetic ballasts may also cause problems for video recording as there can be a so-called "beat effect" between the periodic reading of a camera's sensor and the fluctuations in intensity of the fluorescent lamp.
   BULLET::::- formula_1 light: Normal white sunlight is black-body radiation containing a broad and largely featureless spectrum covering the entire range of human vision.
  
  BULLET::::- formula_2 light: Televisions and computer screens "fool" the eye by generating photons of three narrow wavelength bands where the proportion of photons from industry standard (but improperly named) R "(red)", G "(green)", and B "(blue)" sources is known to be perceived as white.
  
  Section::::Definition.
  
  A perceptual paradox, in its purest form is a statement
  
  illustrating the failure of a formula to predict
  
  what we perceive from what our senses transduce.
   Chromatic adaptation describes the ability of human color perception to abstract from the white point (or color temperature) of the illuminating light source when observing a reflective object. For the human eye, a piece of white paper looks white no matter whether the illumination is blueish or yellowish. This is the most basic and most important of all color appearance phenomena, and therefore a chromatic adaptation transform (CAT) that tries to emulate this behavior is a central component of any color appearance model.
   Section::::The MPACT!
   Section::::Practical issues.:Chromatic dispersion.
   Section::::Alleged concerns regarding prolonged exposure to blue light.:On eye health.:Aggressive marketing.
   In adult individuals a color test like a Farnsworth D-15, a Farnsworth Munsell 100 Hue test can be part of the diagnosis tools and a Berson test makes it possible to distinguish blue cone monochromacy from other diseases. Visual acuity is usually tested in adults and is between 20/60 and 20/200.
  
  Section::::Treatment.
   Thanks to prior development of many groups, including, most notably, Professor Isamu Akasaki's group, Shuji Nakamura at Nichia Corporation and Sony Corporation in Anan (Tokushima-ken, Japan) made a series of inventions and developed commercially viable blue and violet semiconductor lasers. The active layer of the Nichia devices was formed from InGaN quantum wells or quantum dots spontaneously formed via self-assembly. The new invention enabled the development of small, convenient and low-priced blue, violet, and ultraviolet (UV) lasers, which had not been available before, and opened the way for applications such as high-density HD DVD data storage and Blu-ray discs. The shorter wavelength allows it to read discs containing much more information.
    Monochromatic cameras detect shades of gray from black to white and can be effective when sorting products with high-contrast defects.
  
  Sophisticated color cameras with high color resolution are capable of detecting millions of colors to better distinguish more subtle color defects. Trichromatic color cameras (also called three-channel cameras) divide light into three bands, which can include red, green and/or blue within the visible spectrum as well as IR and UV.
   The passbands most optical astronomers use are the UBVRI filters, where the U, B, and V filters are as mentioned above, the R filter passes red light, and the I filter passes infrared light. This system of filters is sometimes called
   Section::::In other media.
  
  Section::::In other media.:Television.
   Each of the three types of cones in the retina of the eye contains a different type of photosensitive pigment, which is composed of a transmembrane protein called opsin and a light-sensitive molecule called 11-cis retinal. Each different pigment is especially sensitive to a certain wavelength of light (that is, the pigment is most likely to produce a cellular response when it is hit by a photon with the specific wavelength to which that pigment is most sensitive). The three types of cones are L, M, and S, which have pigments that respond best to light of long (especially 560 nm), medium (530 nm), and short (420 nm) wavelengths respectively.
   Protanopes, who are missing long wavelength sensitive cones, are unable to distinguish between colours in the green-yellow-red section of the electromagnetic spectrum. They find yellow, red and orange colours to have much lower brightness when compared to a trichromat. The dimming of these colours can result in confusion in many cases, such as when attempting to identify red traffic lights, which appear to be clear. Other colour perception issues include having trouble distinguishing yellows from reds and violet, lavender and purple from blue. In other cases, objects that reflect both red and blue light may appear to just be blue to these individuals.
   BULLET::::- Adjusting the "type" of lights used, so that the light waves emitted are those that are less likely to cause severe light pollution problems. Mercury, metal halide and above all first generation of blue-light LED road luminaires are much more polluting than sodium lamps: Earth's atmosphere scatters and transmits blue light better than yellow or red light. It is a common experience observing "glare" and "fog" around and below LED road luminaires as soon as air humidity increases, while orange sodium lamp luminaires are less prone to showing this phenomenon.
   Diode lasers which emit light at 445 nm are becoming popular as handheld lasers. Lasers emitting wavelengths below 445 nm appear violet (but are sometimes called blue lasers). Some of the most commercially common blue lasers are the diode lasers used in Blu-ray applications which emit 405 nm "violet" light, which is a short enough wavelength to cause fluorescence in some chemicals, in the same way as radiation further into the ultraviolet ("black light") does. Light of a shorter wavelength than 400 nm is classified as ultraviolet.
   Competing research has shown blue light-filtering lenses decrease specific aspects of light emissions. Theoretical reductions in phototoxicity were 10.6% to 23.6%. Additionally, melatonin suppression was reduced by 5.8% to 15.0% and scotopic sensitivity by 2.4% to 9.6%. Over 70% of the participants in this testing were unable to detect these changes. The expansion of technology has led to more individuals utilizing computers and televisions which increase the overall exposure to blue light. This has opened up opportunities for companies such as Gunnar Optiks and Razer Inc. to create glasses focused on reducing the exposure to blue light.
   The violet 405 nm laser (whether constructed from GaN or frequency-doubled GaAs laser diodes) is not in fact blue, but appears to the eye as violet, a color for which a human eye has a very limited sensitivity. When pointed at many white objects (such as white paper or white clothes which have been washed in certain washing powders) the visual appearance of the laser dot changes from violet to blue, due to fluorescence of brightening dyes.
   This same study compared different light colors for glare and detection time under both daylight and night conditions. While red and blue both compared favorably with amber for glare under various conditions, some contradictory findings were observed for detection time. When all colors were held at equal intensity, amber had the poorest detection time both daytime and night. However, when the light source was held at constant intensity, the amber filters, which generally let the most light through, had the best detection time.
  
  Section::::Scientific research.:Potential hazards.
   Research has shown a sensitivity of only 25% for detecting color vision deficiencies, and occasionally the FaLant allows moderate or even severely color deficient trichromats to pass, especially if given enough attempts with allowed errors, or given improperly by the technician. Administration errors are frequent, when not given in the correct lighting conditions, timing or distance.
   The intent of selective yellow is to improve vision by removing short, blue to violet wavelengths from the projected light. These wavelengths are difficult for the human visual system to process properly, and they cause perceived dazzle and glare effects in rain, fog and snow. Removing the blue-violet portion of a lamp's output to obtain selective yellow light can entail filter losses of around 15%, though the effect of this reduction is said to be mitigated or countervailed by the increased visual acuity available with yellow rather than white light in bad weather. 
  