Portable LED-illuminated radiance source

• US 20050270776A1
• Filed: 06/03/2005
• Published: 12/08/2005
• Est. Priority Date: 06/04/2004
• Status: Active Grant

• Current Assignee: The Government of United States of America as Represented by the Secretary of Commerce, The National Institute of Standards and Technology
• Original Assignee: The Government of United States of America as Represented by the Secretary of Commerce, The National Institute of Standards and Technology
• Inventors: Allen, David W., Yoon, Howard
• Granted Patent: US 7,628,507 B2
• Time in Patent Office: Days
• US Class Current: 362/241
• CPC Class Codes: G01J 1/0252 Constructional arrangements for compensating for fluctuations caused by, e.g. temperature, or using cooling or temperature stabilization of parts of the device; Controlling the atmosphere inside a photometer; Purge systems, cleaning devices protection against electromagnetic interferences G01J2001/0276
• CPC Class Codes: G01J 1/08 Arrangements of light sources specially adapted for photometry standard sources, also using luminescent or radioactive material
• CPC Class Codes: G01J 3/0272 Handheld
• CPC Class Codes: G01J 3/0286 Constructional arrangements for compensating for fluctuations caused by temperature, humidity or pressure, or using cooling or temperature stabilization of parts of the device; Controlling the atmosphere inside a spectrometer, e.g. vacuum
• CPC Class Codes: G01J 3/10 Arrangements of light sources specially adapted for spectrometry or colorimetry
• CPC Class Codes: G01J 5/53 Reference sources, e.g. standard lamps; Black bodies
• CPC Class Codes: G01N 21/274 Calibration, base line adjustment, drift correction
• CPC Class Codes: G01N 2201/062 LED's
• CPC Class Codes: G01N 2201/0627 Use of several LED's for spectral resolution

Abstract

An LED-based radiance source that is compact, temporally stable and uniform, and particularly useful in applications such as calibration and characterization of radiation thermometers, night vision devices, environmental remote sensing systems, biological agent detection, and any radiometer which needs a stable radiance source. The LED-based radiance source is a suitable replacement of lamp-based integrating sphere sources where they are used as stable and uniform radiance sources. The LED-based radiance source includes an array of LEDs having substantially similar radiance output wavelengths and a radiation detector such as a photodiode that detects and monitors radiation directed from the LEDs. Temperature of the LEDs can be controlled by feedback from the photodiode, thereby allowing for control and stabilization of temperature-dependent radiation output.

Claims

1. An LED illuminated radiance source which comprises:

a housing having first and second ends;

an array of LEDs provided at the first end of the housing and arranged to direct radiation toward the second end of the housing; and

a radiation detector coupled to the housing between the first and second ends for detecting radiation directed from the LEDs through the housing.

2. An LED illuminated radiance source according to claim 1, further comprising a cooling element coupled to the array of LEDs.

3. An LED illuminated radiance source according to claim 2, further comprising a temperature sensor coupled between the array of LEDs and the cooling element.

4. An LED illuminated radiance source according to claim 3, wherein the cooling element comprises a thermoelectric cooler.

5. An LED illuminated radiance source according to claim 1, further comprising a diffuser covering the second end of the housing.

6. An LED illuminated radiance source according to claim 5, wherein the diffuser comprises at least one of a ground-glass diffuser, an acrylic diffuser and an opal glass diffuser.

7. An LED illuminated radiance source according to claim 3, wherein the temperature sensor is electrically coupled to the cooling element for controlling the temperature of the array of LEDs.

8. An LED illuminated radiance source according to claim 1, wherein the radiation detector comprises a photodiode.

9. An LED illuminated radiance source according to claim 1, wherein the array of LEDs comprises a plurality of LEDs that each generates substantially the same wavelength of radiation.

10. An LED illuminated radiance source according to claim 9, wherein the plurality of LEDs each generates radiation at a wavelength of one of 395 nm, 660 nm and 950 nm.

11. An LED illuminated radiance source according to claim 1, wherein the housing includes an inner layer of polytetrafluoroethylene.

12. An LED illuminated radiance source according to claim 1, wherein the housing has a generally cylindrical shape.

13. An LED illuminated radiance source according to claim 1, wherein the array of LEDs comprises a plurality of LEDs that are mounted on a circuit board.

14. An LED illuminated radiance source according to claim 1, wherein the array of LEDs comprise a plurality of LEDs that are fabricated directly on a substrate.

15. The LED illuminated radiance source according to claim 1, wherein the array of LEDs comprises a removable module that is configured to insertion, removal and replacement within the housing.

16. A compact LED radiance source that comprises:

a tubular housing having first and second ends;

a replaceable LED module that comprises a plurality of LEDs having substantially similar radiance output wavelengths; and

a radiation detector coupled to the housing between the first and second ends for detecting radiation directed from the LEDs through the housing.

17. A compact LED radiance source according to claim 16, wherein the replaceable LED module further comprises a cooling element and a temperature sensor.

18. A compact LED radiance source according to claim 16, wherein the temperature sensor is electrically coupled to the cooling element for controlling the temperature of the array of LEDs.

19. A method of providing a stable, uniform source of radiation which comprises the steps of:

a) providing a plurality of LEDs having a common wavelength;

b) supplying current to the plurality of LEDs to cause the plurality of LEDs to emit radiation;

c) monitoring the radiation emitted from the plurality of LEDs; and

d) using the monitored radiation in step c) to control at least one of the temperature of the plurality of LEDs and the current supplied to the plurality of LEDs.

20. A method of providing a stable, uniform source of radiation according to claim 19 further comprising the step of providing the radiation as a calibration or reference source for at least one of a radiation thermometer, night vision device, environmental remote sensing system, and biological agent detection system.

21. A method of providing a stable, uniform source of radiation according to claim 19 further comprising the steps of providing a standard radiance level scale and using the monitored radiation in step c) to maintain the radiation emitted from the plurality of LEDs relative to the standard radiation level scale.