Light sources include light bulbs and stars like the Sun. Reflectors (such as the moon, cat's eyes, and mirrors) do not actually produce the light that comes from them.
When we look at a leaf, we know that it is green because the light bounces off the leaf to our eyes to indicate that it is green. But what is light? What are the sources from which the light originates? Light is electromagnetic radiation. A particular frequency of this radiation (around 390-700 nm) is visible to the human eye. Everything we see around us is due to light. Light is a form of energy and, like all energies, it is produced from a source. In physics, they are called light sources.
There are countless sources of light, but they can all be categorized under either of the two following categories.
The universe is full of objects that emit light, some light from these sources reaches the earth. The following things in nature have the ability to emit light:
The Sun is the main source of light on Earth, this energy comes out as heat and light; Sunlight is one of the main factors behind the sustainability of life on earth, all other stars also produce light, but only a small or no amount reaches the earth due to the great distance. The moon also provides light, but it cannot produce light on its own. The light we get from the moon is reflected by it from the sun.
Some living organisms also have the ability to produce light. It's called bioluminescence. Examples include fireflies, jellyfish, certain deep-sea plants, and microorganisms. Some other natural phenomena such as lightning and volcanic eruptions also emit light.
Apart from natural sources, light can also be produced artificially. The different artificially produced light sources can be classified into three general categories:
When certain objects are heated to a high temperature, they begin to emit light. Both infrared and visible light are produced in the process. Example: candle, incandescent lamp.
Light can be produced by accelerating charges in a luminescent material. A common way to do this is by avoiding current through the material. Example: fluorescent tube light, electric bulb
Passing electricity through certain gases at very low pressure can also produce light. Example: neon lamp, sodium lamp.
Slit lamp: It has a light source whose intensity, height and width can be modified according to needs. The light beam is directed at a focus that coincides with the focus of the observation system.
Click-off: Allows misadjustment of the lighting system direction for indirect lighting techniques.
Diffusing lens: Frosted lens. Placing it in front of the light source diffuses it and produces a homogeneous illumination on the anterior pole. If we place it, we get an image without much detail, but the patient will not be so bothered by the light. It is used to observe structures at a general level but, above all, for ophthalmic photography.
Filters: Antipyretic, polarized, cobalt blue and green. With them we improve the observation of some ocular structures.
Coaxial displacement: The focus of the light beam coincides with the focus of the observation system and both systems move around this common focus.
PARELELEPÍPEDO: Direct light with a width of ½ and 3mm. The lighting arm may be between 30º and 45º. The magnifications can be set between 10x - 40x and a medium light intensity. It can be used to examine the transparency of the lens. To focus all the layers of the lens, it is enough to move the biomicroscope from the pupillary area inwards, in a movement of greater amplitude than to observe the different layers of the cornea, for example. The observation angle can range from 10º to 45º. With this illumination we observe lens opacities, congenital cataracts, cortical cataracts, subscapular cataracts and opacification of the subscapular membrane. After cataract surgery, an opacification in the cataract is visible by directing the light towards the pupillary area and focusing the different layers in an anteroposterior movement and vice versa.
OPTICAL SECTION: Observation system in front of the eye and lighting system at a variable angle between 30º and 60º. The bundle is narrowed to the maximum until a transverse histological section is obtained. Light intensity to the maximum and the increase we place it between medium and high. Sometimes, since the pupil is small, it is useful to decrease the angle of both systems. With this, we can observe the different layers of the lens. The presence of nuclear sclerosis is assessed with this illumination technique by the presence of a yellow-brown color in the nucleus of the lens.
SPECULAR REFLECTION: It is a parallelepiped shape, in which the angle of incidence of the light beam on the observed surface is equal to the angle of the observation axis through the eyepieces, and with this specific angle of maximum reflection we will observe a bright specular reflection of the different surfaces of the anterior segment, including the two faces of the lens. It allows us to observe the quality of the anterior surface of the lens or if there is any pathological process.
INDIRECT PROXIMAL LIGHTING: Similar to direct lighting with parallelepiped with medium-high luminosity, except that we are observing a condition not directly lit, but located to the side. This allows the object and the area around the object to be illuminated with light scattered through the lens. Thus, it is possible to more accurately detect the degree of loss of transparency of it.
BACKLIGHTING: Lighting system between 0º and 10º from the observation. Narrow slit and medium to high magnification. Medium-high magnification. As the slit is directed towards the retina, the retina behaves like a concave mirror and reflects light towards the observer. Useful for evaluating cortical cataracts and subscapular cataracts. Less useful for evaluating nuclear cataracts, since these present a more homogeneous loss of transparency.