The Pen Perspective

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***Post 1, LED's are not for Reading*** *Unix Epoch: 1562644800*

It's now been a while since 60 Watt incandescent bulbs have been banned nearly worldwide. I have tried several Light Emitting Diode (LED) lamp fixtures and I always have difficulties reading by the spectrum deficient beam. Human eyes evolved, just like all land based biological eyes, to respond to reflected light originating from our yellow/green star, Sol. That evolutionary development has resulted in an eye that has a well adapted set of sensors calibrated specifically for viewing details in bright sunlight. The blue cones are the most sensitive, while red cones are the [least sensitive][1]. This is why blue LEDs appear so bright to the human eye, and why red LEDs and red tinted lights are used to maintain acclimation to the dark. There is no such thing as a white LED. They are only capable of emitting a single wavelength of light. This is a function of the physics involved in LEDs. The junction material absorbs electrical energy and releases a photon when an excited electron drops back down to its natural energy level. Since the material consists of very specific materials, the photons released all fall within a specific wavelength. Interestingly, standard diodes also emit photons, but outside the range of human vision. This is not the case with standard incandescent bulbs, halogens, sodium vapor, or other non-linear gas/material light sources. Incandescent bulbs work by heating a filament. The hot filament emits a photons with a broad range of energy. This results in broad chromatic spectrum emission, very unlike LEDs... but similar to sunlight. Since white LEDs do not exist, every LED lamp that appears white is either actually a collection of LEDs emitting a few narrowband but intense frequencies of visible light or a high intensity blue LED coated with phosphor. The blue LED plus phosphor coating is the preferred method for most household "white" LED lamps. However, this method of construction produces a spectrum with a large peak in the blue frequency range. See [this datasheet][2] for an example.

*Image Source:* Previous linked [data sheet][2] The manufacturers of "white" LED lamps use a misleading metric called "color-temperature" in order to make the claim that the LED spectrum is similar to daylight from the Sun. But it is not. The intense blue peak from "white" LEDs hits my aging cones in my eyes and causes me to have trouble focusing on a page of paper in my many books. Intense blue light has also been linked to [unbalanced melatonin][3]. So, I have taken to replacing all my incandescent lamps with halogen lamps or the larger wattage recessed flood lamps. Thus, the LED transformation has ruined my reading experience, my eyes, and raised my energy usage and costs. [1]: http://hyperphysics.phy-astr.gsu.edu/hbase/vision/rodcone.html [2]: https://download.luminus.com/datasheets/Luminus_MP3014_1100_Datasheet.pdf [3]: https://www.health.harvard.edu/staying-healthy/blue-light-has-a-dark-side
Originally posted here: https://steemit.com/science/@thepen/the-pen-perspective