Red light has longer waves, with wavelengths around to nm. Blue light has a higher frequency and carries more energy than red light. According to research, red light therapy is safe for eyes, but precautionary measures must be taken. It should only be administered by a doctor and not self-administered at home.
Unlike ultraviolet UVA and UVB light, red light will not burn your eyes, although you may feel a gentle warmth during treatment. Continued exposure to blue light over time could damage retinal cells and cause vision problems such as age-related macular degeneration.
It can also contribute to cataracts, eye cancer and growths on the clear covering over the white part of the eye. Photodynamic therapy, or Blue Light, is a treatment that uses special drugs, called photosensitizing agents, along with light to kill targeted cells. Used to treat sun-damaged skin, this procedure involves applying a topical medication to the skin.
Your computer screen might be aging you. First, blue light hurt your eyes. Now, studies suggest it might damage your skin, too.
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Or can it be somewhere else along the curve of the peak as long as it is consistent among all the measurements and still get an accurate result? If there are two colored specimens in the same solution, it is actually better to measure at the wavelength where the difference between the spectra is as high as possible.
For spectrophotometric analysis, we normally choose the wavelength of maximum absorbance for two reasons:. From differential analysis. Further [1, p. Measurements should be made at a wavelength of maximum absorbance. Sign up to join this community. The best answers are voted up and rise to the top. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Learn more. When making a calibration curve, do we have to use the wavelength at maximum absorbance?
Organic compounds, especially those with a high degree of conjugation, also absorb light in the UV or visible regions of the electromagnetic spectrum.
The solvents for these determinations are often water for water soluble compounds, or ethanol for organic soluble compounds.
Some organic solvents may have significant UV absorption; not all solvents are suitable for use in UV spectroscopy. Ethanol absorbs very weakly at lower ultra-violet wavelengths. Solvent polarity and pH can affect the absorption spectrum of certain organic compounds. The output of a spectrophotometer is a spectrum usually. A spectrum plural spectra is a graph displaying either values for transmitted, absorbed, or reflected light Y axis vs. Here the wavelength is scanned while the ordinate value is recorded to produce a spectrum as seen above.
Instruments scan from longest wavelength to shortest. Data can be collected as either peak height or area. Standards are measured first and can consist of either one or many different concentrations. Concentrations of the standard are then analyzed and graphed using a least squares statistical analysis seen above. Unknown samples can be calculated from the line fitting equation.
If only a single standard is used, linearity is assumed. Photometric mode allows for a table of wavelengths to be defined and collected. This process is usually performed to save time since this function is quicker than a wavelength scan. Frequently used for kinetic analysis to investigate samples changes over time. For each wavelength of light passing through the spectrometer, the intensity of the light passing through the sample cell is measured.
The intensity of light entering the sample is usually referred to as I 0. The intensity of the light passing through the sample cell and emerging on the other side is usually designated I 1. If I 1 is less than I 0 , then obviously the sample has absorbed some of the incident light. A simple bit of mathematics is then done in the computer to convert this into something called the absorbance of the sample, given the symbol, A sometimes abs. The absorbance is a measure of the amount of light that disappears interacts with the sample.
The Beer-Lambert Law above , is the relationship between absorbance as a function of sample concentration c, the sample extinction coefficient a, the sample path length L, I 0 , and I 1 is given by:. For most inexpensive spectrophotometers you will come across, the absorbance ranges from 0 to 3, but it can go higher than that for more expense instruments.
An absorbance of 0 means that no light of that particular wavelength has been absorbed by the sample. Absorbance is a logarithmic scale similar to the Richter Scale used for earthquakes. Thus an instrument that can measure to 3 absorbance units has a range of 3 orders of magnitude. Molar absorptivity is a constant for a particular substance, so if the concentration of the solution is halved so is the absorbance, which is exactly what you would expect.
A compound with a high molar absorptivity is very effective at absorbing light at the stated wavelength, and hence low concentrations of a compound with a high molar absorptivity can be detected at lower concentrations.
In addition, the absorbance value at a given wavelength can be calculated if you know the molar absorptivity, path length, and concentration. So far we have considered only the amount of light entering and exiting the sample.
There are three other important factors related to the sample that define the absorbance. The extinction coefficient is a physical property of the molecular bonding chemical structure of the sample compound. The same molecule will always have the same value for a at the specified wavelength. The important feature of the a value is that it is a constant for the unique chemistry of the sample and will only change when the chemistry changes.
The take home message is that. Concentration and path length have a linear proportion relationship with the absorbance value. It is vital in chemistry to understand the difference between amount of a sample and the concentration of a sample.
An amount is a quantity of something; a concentration is an amount of something in a volume of something else. So 10 grams of sugar is an amount, while 10 grams of sugar dissolved in milliliters of water is concentration.
Amounts in chemistry are usually expressed as moles; whereas concentrations use the term molar. A mole of something is the molecular weight for the compound expressed as grams. So if the molecular weight of a compound is , then one mole of that com- pound would be grams. A one molar solution would be grams dissolved in one liter of solvent water.
An example, now, suppose we have a solution of copper sulphate which appears blue because it has an absorption maximum at nm. We look at the way in which the intensity of the light changes as it passes through the solution in a 1 cm cuvette. We will look at the reduction every 0. For our illustration, we will suppose that this fraction is 0. This data can be graphed to better see the relationship. However, for absorbance the relationship is a straight line lower left.
Scientists love straight lines rather than curves. Because it is easier to mathematically model a straight line as opposed to a curve. If we plot absorbance at the peak wavelength against concentration, we get a straight line passing through the origin 0,0. With absorbance we can use spectroscopy to measure how much of something is present. This high energy light, compared to near infra-red, has enough energy to cause electronic transitions.
These types of transitions move electrons from low energy levels, in an atom or molecule, to higher energy levels. First, we will explain what happens when organic compounds absorb UV or visible light, and why the wavelength of light absorbed varies from compound to compound.
Put simply the energy from the light is imparted to the electrons involved in chemical bonding. This causes the electrons to be promoted moved to a higher energy level; thereby, absorbing the light energy.
These energy levels are associated with the bonding and anti-bonding orbitals of conjugated double and triple bonded carbon atoms or aromatic benzene type ring systems in organic molecules.
When light passes through the compound, energy from the light is used to promote an electron from a lower energy bonding or non- bonding orbital into higher energy empty anti- bonding orbitals. The possible electron jumps that light can cause are seen in this slides figure upper right.
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