LED light standard for photo- and videomicroscopy
First Claim
1. A light calibration device comprising diffused LED light source, control means to provide feedback control of intensity, said control means including a photodiode positioned to detect output light intensity from said diffused LED source, light diffuser means, said diffused LED source being encapsulated in said diffuser means, whereby the light from said LED light source is homogenized and a flat field of illumination is obtained.
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Abstract
The invention relates to a light calibration system consisting of a compact LED source with feedback control of intensity. The source is positioned in the focal plane of the microscope objective and produces flat-field illumination of up to 31 microwatts. The source can be easily used to determine the performance of microscope optics and camera response. It can also be used as a standard light source for calibration of experimental systems. Selectable light intensities are produced by controlling the LED input power via a feedback circuit consisting of a photodiode that detects output light intensity. Spectral coverage extends between 550 nm and 670 nm using green, yellow and red LEDS mounted side-by-side and which are individually selected. The LED chips are encapsulated in plastic diffusers which homogenize the light, and a flat field of illumination is obtained through a thin 1 mm diameter aperture positioned directly over each chip. Provision is made for insertion of Ronchi rulings over the aperture to enable measurements of contrast modulation in a uniform field. The light can be pulse-modulated to assess camera response times and the device can be synchronized with video frames. Narrow bandpass interference filters can be placed between the objective lens and the LED source to produce monochromatic light without affecting the spacing of controlled light intensities since emission spectra do not appreciably shift over the range of LED powers chosen in this design.
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Citations
20 Claims
- 1. A light calibration device comprising diffused LED light source, control means to provide feedback control of intensity, said control means including a photodiode positioned to detect output light intensity from said diffused LED source, light diffuser means, said diffused LED source being encapsulated in said diffuser means, whereby the light from said LED light source is homogenized and a flat field of illumination is obtained.
- 11. A light calibration device comprising an LED light source, control means to provide feedback control of intensity, said control means including a photodiode positioned to detect output light intensity from said LED source, said LED light source is at least one chip, and a thin aperture member positioned directly over each of said at least one chip, the aperture diameter of said aperture member being on the order of about 1 mm.
- 17. A microscope having light calibration device, comprising an LED light source, control means to provide feedback control of intensity, said control means including a photodiode positioned to detect output light intensity from said LED source, said LED light source is at least one chip, and a microscope objective lens, said LED source being in the focal plane of said microscope objective lens.
Specification