Frequently Asked Questions
Unlike ordinary incandescent bulbs, LEDs do not have a filament that burn out. LEDs emit light when electricity runs through a semiconductor material, which, in turn, excites electrons.
Compact, energy efficient, and economical, LED illumination is a great choice for both industrial and laboratory applications. Available in different configurations, such as ring lights, backlights, domelights, or arranged in custom configurations, LEDs can be easily integrated into virtually any illumination task. A main advantage of LED illumination is the freedom to easily select white, IR, RGB, or specific wavelength outputs in a variety of different geometries. An RGB output is recommended for applications that require user adjusted color balance, while Red and IR LEDs are a great choice for monochromatic applications. LEDs are also able to be strobed and/or overdriven, which can often be an invaluable function for high speed imaging applications on assembly lines. Intensity control is also possible with certain intensity controllers and power supplies. Very long lifetimes with predictable intensity fall-off are further benefits of using LED illumination sources.
There are 3 possible solutions to maximize the amount of light when coupling light from a LED to a fiber. First, using Infinity Corrected Microscope Objectives in retro position; this works well but is by far the most expensive solution. Second, we offer Fiber Optic Collimator/ Focuser Assemblies, available with an SMA or FC connector for VIS, VIS-NIR and IR wavelengths. You can achieve spot sizes of a few microns. This product offers the best value for its price. Last, but not least, are Ball Lenses; these are the least expensive solution. When coupling light from a LED into a fiber, the choice of ball lens is dependent on the Numerical Aperture (NA) of the fiber and the LED’s spot diameter. The LED’s spot diameter is used to determine the NA of the ball lens. The NA of the ball lens must be less than or equal to the NA of the fiber in order to couple all light into the fiber. The tricky thing with ball lenses is alignment. View Understanding Ball Lenses for additional information and useful equations.
There are multiple ways to achieve the effect you require; however, the most straightforward is utilizing Darkfield Illumination. Darkfield Illumination is ideal for imaging transparent or translucent objects. Light from the Darkfield illuminator, usually a special type of ring light guide, enters the object through the edge, rather than from above, enabling one to see the object’s profile. View Choosing the Correct Illumination for additional information on pros and cons of various illumination setups.
Fiber Optic Illumination
Fiber optic light guides transmit light based on the principle of total internal reflection. Light incident on cylindrical fibers of either acrylic or glass materials can be transmitted through these fibers with little attenuation.
Useful for applications with very tight space or limited access constraints, Fiber Optic Illumination can provide a wide range of useful illumination geometries from spot lights and ring lights to diffuse sources and line lights. Light guide optics are also able to brave certain environments where using electronics would otherwise be a danger. Fiber optic illumination can also be intensity controlled and very easily aimed towards objects. Broadband illuminator sources provide white light illumination, which is composed of all of the colors of the visible spectrum.
"Ripple" is a sinusoidal fluctuation of light intensity. This can cause a problem with machine vision systems that utilize computer algorithms, when constant contrast is required for proper data acquisition. The AC current powering the illumination source causes this ripple in illumination systems. Illumination sources can be DC regulated, which nearly eliminates this ripple effect. Our Dolan-Jenner DC-950H Regulated Fiber Optic Illuminator offers = 0.4% ripple.
Fiber optic light guides such as our Flexible Fiber Optic Light Guides consist of a bundle of high transmission glass fibers that can be used in conjunction with fiber optic illuminators to provide intense visible illumination. Fiber optic light guides and their respective illuminators are typically used for most fiber optic illumination applications. Quartz (or fused silica) fiber optic light guides such as our Quartz Fiber Optic Light Guides are designed for ultraviolet and infrared applications. They are ideal for UV transmission, but will transmit in the visible as well. They will also show some fluorescence at 245nm and darken in gamma or x-ray environments. These plastic-clad quartz fibers provide maximum transmission efficiency due to the 10:1 core/clad ratio and high flexibility from their small fiber diameter. Liquid fiber optic light guides such as our Liquid Light Guides are also ideal for visible and ultraviolet light applications. Unlike glass fiber optic bundles, liquid light guides are actually composed of liquid and do not suffer from packing fraction losses (spaces between fibers that cause reduced coupling efficiency).
Fiber optic light guides, like optical fibers themselves, do not produce beam-like outputs. They are very good for transmitting light and produce rather quickly diverging cones of light. Due to symmetry principles in fiber optics, the output angle of a fiber is approximately the same as the input angle.
The full acceptance angle is defined as the maximum allowable input/output angle for each light guide and is directly related to the numerical aperture specification (NA). For instance, our typical glass fiber light guides will accept a cone of light approximately 68°, which corresponds to 0.55. Quartz UV light guides have an acceptance angle that is dependant on wavelength and fiber bundle length; for our 36"" length UV guides, the angles are 42° at 254nm and 35° at 546nm for bundles fully illuminated by a source at half intensity. If the input angle, say 30°, is smaller than the acceptance angle, say 68°, then the output angle will still be 30°, not the 68° that one might think. If a fiber is overfilled, the output angle will be slightly less than the acceptance angle due to losses. Using light guides in conjunction with our Fiber-Lite Focusing Lenses will allow the output beam to be focused or collimated.
Glass fiber optic light guides have several characteristics that contribute to loss in transmission. The most common are cladding loss between the core and cladding diameters, packing fraction loss due to gaps between individual fibers and fresnel losses due to reflections of the end faces. Additional factors include extreme bends over long durations, glass fracture cracks due to bending, and cross-talk between individual fibers. Typically, the total effect is a transmission loss of 6% per foot (visible light) with an illuminator-to-light guide coupling loss of approximately 30%.
An adapter is required to connect our Fiber Optic Light Guides to our Fiber Optic Illuminators which all have a standard 25mm diameter opening port. Our Light Guide Adapters are metallic bushings with a ring shape designed to fit in the open aperture of our various illuminators. The light guide is inserted into the center hole of the adapter. The adapter and light guide are then held within the illuminator's aperture by a set screw. To select the correct adapter, you must match up the inner diameter of the adapter and the end-tip diameter of the light guide.
Both the #39-606 EKE and #59-477 EKE-X bulbs can be used with our line of Quartz Halogen Illuminators. The two bulbs are packaged in the same housing and feature the same spectral range. However, the main difference is that the EKE-X has a longer lifetime but lower intensity profile than the EKE. The average lifetime of the EKE-X is 1000 hours while the average lifetime of the EKE is 200 hours.
Strictly speaking, there are optical designs which enable fiber coupling without first collimating the output of the diode laser, but all of these designs suffer from massive astigmatism which can significantly reduce the efficacy of the fiber coupling. Having a collimated beam inside of the laser package allows for the addition of optical elements such as micro-optical isolators and bandpass filters.
The radius a fiber optic strand or light guide can be bent without risking breakage or increased attenuation is called the bend radius. Edmund Optics® lists the bend radius for all its optical fibers and light guides.
High frequency illumination provides a flicker and ripple free output that assures image quality by maintaining constant frame to frame gray level. Fluorescent lights are the best example of high frequency illumination. When determining the correct illumination for one's camera setup, make sure the frequency of the illumination is higher than the frame rate of the camera. This will help to insure constant illumination and therefore the best image quality from frame to frame. Correspondingly, high frequency illumination helps reduce operator fatigue and eye strain when used over long durations.
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