Radiant energy – Photocells; circuits and apparatus – Photocell controls its own optical systems
Patent
1993-10-15
1996-02-06
Sikes, William L.
Radiant energy
Photocells; circuits and apparatus
Photocell controls its own optical systems
315181, 315182, 315183, 315180, H05B 3500, H05B 3700
Patent
active
054897718
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.
REFERENCES:
patent: 4284884 (1981-08-01), Dyment et al.
patent: 4292513 (1981-09-01), Simmons et al.
patent: 5374876 (1994-09-01), Houhata et al.
Beach James M.
Duling Brian R.
Abraham Fetsum
Parker Sheldon H.
Sikes William L.
University of Virginia Patent Foundation
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