Photometry Tutorial

This Photometry Tutorial is aimed at giving you a brief overview of photometry.  Let us start with the basic definition of photometry. In simple words it is the science of measurement of visible light. When I say visible light I mean the light in the wavelength range of 400 to 700 nm. I like to share this Definition of Atomic Radius with you all through my article.

About what is Photometry, there is a much simpler answer. The measurement of the light is done in terms of the intensity in which it is received or perceived by human eyes. As we know that the human eye does not perceive each and every wavelength of light equally. It has different perception for different wavelength. So we have a factor in this topic which accounts for the level of perception of human eye, different for different wavelengths. In this way the required measurement is done for each and every wavelength.
The SI units for this are Candella or lumens etc. There are various instruments called photometers that are used for the measurement purposes. They can be used for lights with different wavelengths and different intensities and flux.

Aperture format is another application of normal photometric techniques. When we use a CCD camera various techniques can be applied to measure the light. One such technique is aperture photometry. In this the rays of light coming from the object from different points will be added while those coming from the sky will be averaged out and subtracted. In this way we can clearly measure the light from the object.
The technique used in Differential format is entirely different. The light coming from the object over time is measured. It will be then averaged to form a light curve. In some cases all the observation are just mapped to form the curve.

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The changes measured are over a significantly long interval which can range from days to months. High precision can be obtained when such a technique is used which is not the case if we use absolute form of this.
It should be noted that the light coming from the atmosphere can also vary over time while using the differential techniques. This is also taken into account and averaged out accordingly.

These are covered under the same light curve in most the time, but sometimes it can have individual curves as well.

It has many uses. It is also used in chemistry for measuring the light coming from the chemical solutions etc.