Glossary

There are a number of terms we use with varying degrees of technicality. For your convenience we have included some of these here. Each term is linked directly to its corresponding Wikipedia page if you want to dive deeper. Feel free to use this as a reference or read through the whole thing before jumping into Aletheia.

UNDER CONSTRUCTION

ATP - (or adenosine triphosphate) is the way energy is transported in the body. You can think about it as a sort of 'wrapper' of electrons.

Blackbody Radiation - the light that all objects emit in a spectrum that depends on their temperature.

Candela - lumens per amount of your field of view e.g. the candela from a car headlight is relatively high because there is a high amount of luminosity coming from a narrow area. Yet, the total 

Circadian Rhythm - the 24 hour clock that regulates biological processes and is present in all human cells.

Cone Cells - the cell in your eyes that interpret light based on the primary colors of red, green, and blue. These cells are responsible for image formation.

Color - a perceptual phenomena of light experienced by people and animals. Perceived color is not a direct representation of the physical properties of the light being perceived. 

Color Rendering Index - an absolete metric of light quality that should have never existed. See the TM-30 standard for how the quality of light can be effectively evaluated.

Color Space - a set of colors, usually describing a set of colors achievable given some combination of colors whose respective intensities may vary.

Complex System - a group of interacting components where the interactions among the various components give rise to phenomena that cannot be anticipated merely by evaluating each individual component independently. e.g. weather, markets, or the human body

Cytochrome C Oxidase - a mitochondrial enzyme suspected to play a key role in the mechanisms underlying the profound effects of near-infrared light. 

Efficiency - the amount of power coming out divided by the amount of power going in. Efficiency metrics must define the particular input and output being looked at in order to be meaningful. In lighting, radiant efficiency measures radiant energy per input energy as opposed to luminous efficiency, which can be gamed by making the quality of the light worse. 

Electric Current - the rate at which electrical charge is passing through some cross-section.

Electromagnetic Radiation - light, including non-visible.

Electron - a fundamental particle that carries energy and a charge. Electrons emit photons when they decrease in energy and increase in energy when they absorb photons.

FDA Registered - usually refers to a product that has been deemed equivalent to something that already exists so that people can rely on it being no more dangerous than something else. It has practically zero bearing on efficacy and is often used as a marketing gimmick.

Frequency - how often something happens per unit time, usually measured in Hertz (Hz). 1 Hz means once per second. Frequency of light tells you how many waves pass by each second. For each frequency there is a single corresponding wavelength and vice versa.

Hemoglobin - transporter of oxygen in blood cells

Infrared Light - light with a longer wavelength than red light (on the opposite side of ultraviolet).

Inner Product - a form of multiplication that is critical to understanding the biological effects of light. Given a cell in the body that responds with varying intensity to light of different wavelength, the inner product adds up the contributions of a source signal in each region weighted by that sensitivity.

Irradiance - flux density, intensity, the amount of light received by a surface per area.

Joules - a unit of energy e.g. 4,186 joules are needed to raise the temperature of a liter of water by 1 degree C.

LED (light-emitting diode) - a semiconductor device that emits photons when current passes through it. LEDs are far more energy efficient than other devices.

Light - electromagnetic waves / photons.

Lumens - the total amount of light from a source, weighted by the the perceived brightness of each wavelength. Lumens are NOT proportional to melanopic lux.

Luminosity Function - the function that describes how brightly we perceive various wavelengths compared to the wavelength perceived as having maximal brightness.

Lux - Lumens per square meter.

Melatonin - A hormone associated with sleep, that is also correlated with various health benefits. Oral supplementation of melatonin may not be as effective in attaining these benefits.

Melanopsin - the photopigment that absorbs light in a region of wavelengths spanning from blue to green. This pigment is found in ipRGCs (intrinsically photosensitive retinal ganglion cells), which were only recently in discovered in 1999! These cells are independent from image-forming cone-cells and they are even perfectly functional in blind people.

Melanopic Lux - ordinary lux is based on areal concentration of lumens, which is itself based on perceptual brightness. Melanopic lux on the other hand is weighted in proportion to the extent to which a light source stimulates melanopsin. For a constant light and optics, doubling the lux doubles the melanopic lux, but two lights yielding the same lux level are unlikely to deliver the same melanopic lux. Light spectrums vary enough that these differences can be substantial. 

Metamerism - the fact that every color (a mere human perception) can be generated by infinite possible spectrums of light. All that matters is that each of the 3 cones is triggered by the same amount for two spectrums of light to have identical colors. Importantly, the same colors can have different amounts of melanopic lux depending on how they are generated. 

Milli- (prefix) - a thousandth. This is the most common prefix we will use, in particular with near-infrared light. 

Mitochondria - "the powerhouse of the cell". Responsible for the generation of ATP. Mitochondrial dysfunction is implicated in various diseases. Healthy and abundant levels of mitochondria are correlated to aerobic fitness and overall health.

Neurodegenerative Diseases - any disease involving progessive failure of the brain and cognitive functions e.g. Alzheimer's and Parkinson's

Nitric Oxide Synthase - precursor to nitric oxide, a vasodillator that increases bloodflow. Its upregulation by near-infrared light is one of the proposed mechanisms for enhancing the healing rate of various tissues.

Non-Ionizing - light where the energy of each photon is too low to strip an electron from an atom (ionization) e.g. visible, infrared, and longer wavelengths. Importanly, non-ionizing does not mean biologically inactive. Ionization is merely one of many ways that light can interact with biological matter.

Nonlinear - when the change in some variable leads to a disproportionate change in some other variable. Many things in the real world are non-linear, which makes it harder to understand how various things interact and will respond to a given stimulus.

Non-thermal light (pseudoscience) - near infrared light is sometimes incorrectly referred to as 'non thermal' or 'non-heat generating' by people who have a poor grasp of high school level physics (probably most people). While the research on near-IR has shown that it has a number of photochemical effects, all light carries energy, and this becomes heat when it is absorbed. Low-doses of near-IR may have imperceptible heat, but the most effective doses can easily reach an energy level resulting in noticeable heat.

Phosphor - a material that absorbs, and then emits photons. The emitted photons are often of a different color. White LEDs usually have a single peak wavelength combined with phosphors to generate a wide range of wavelengths.

Photochemical - chemical effects that result from incident photons.

Photon - a particle of light.

Power - the rate at which work is being done or energy is being transferred.

Radiant Exitance - flux density, intensity, the amount of light emitted by a surface per area.

Sia La - a mountain pass by the Siachen glacier known for being the highest battleground on Earth (at 17,000 ft), but also for the beautiful red roses (Sia means rose in Balti, a language spoken in parts of the nation of Tibet). Did you think we meant something else by 'Sia La Lux'? ;)

Spectral Power Distribution - the amount of power at each wavelength.

Steradians - the unit of measure for a solid angle. The 3 dimensional equivalent of degrees (0 to 360 for a circle). Since light can come from any point, we use this to think about the percentage of the field of view from which we are seeing light. This indicates how diffuse or intense the light is.

Transmittance - when light encounter anything, transmission (passing through) is one of the three things that can happen. Transmittance evaluates how much light of each particular wavelength can pass through. Other things that can happen to light are that it can bounce back (reflection), or it can be absorbed, energizing a photon and delivering heat.

Ultraviolet Light - light with a shorter wavelength than visible violet light (higher energy photons). It is on the opposite side of the spectrum compared to infrared. UV light is critically important to health, but it also can pose (when exposure comes in conjunction with other unhealthy lifestyle activities) since it is ionizing.

Vector Space - more or less, a collection of objects called vectors, each of which is a collection of elements. It's actually far simpler than it sounds. Imagine you go to Chipotle to order a burrito. All the possible burritos that can be ordered at Chipotle form a vector space. Every burrito that gets ordered is a vector. The ingredients in that burrito are the elements of the vector.

To make it a vector space, you just need to add addition and multiplication, and burritos can handle that just fine. Want to add two burritos together? No problem. You now have a bigger burrito that is also a member of the Chipotle vector space. Want to multiply two burritos together? Just multiply the amounts of each component and enjoy your MASSIVE burrito.

Why might you want to know about vector spaces? Because that is where light and color live. There are only a few dozen burrito ingredients, but light can come in infinitely many wavelengths (infinite vector space). In the real world, usually we encounter a mix of different wavelengths, which is like a burrito of light. You can add together different spectral distributions of light to get a new one, or you can combine a filter and a single light source to get a new one.

VEGF (Vascular endothelial growth factor)

Viscosity

Visible Light Spectrum

Voltage

Wavelength

Watts - standard unit of power. A watt is one joule of energy per second.

Zeitgeber - a signal or cue to the body e.g. certain wavelengths of light indicating that it is daytime and halting the secretion of melatonin.

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