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`US005905268A
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`United States Patent
`
`[19]
`
`[11] Patent Number:
`
`5,905,268
`
`Garcia et at.
`
`[45] Date of Patent:
`
`May 18, 1999
`
`250/4931
`7/1987
`4,683,379
`250/461.1
`1/1995
`5,383,776
`313/112
`5/1995
`5,412,274
`359/890
`9/1995
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`5,674,000 10/1997 Kalley ..................................... 362/293
`Primary Examine_r—Bruce Anderson
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`An inspection lamp for detection of a fluorescent material
`which absorbs electromagnetic energy in a specific excita-
`tion frequency band and which emits electromagnetic
`energy in a specific fluorescent emission frequency band
`within the Visible light spectrum. The lamp includes a bulb
`,
`g, and a
`housing a light source within the bulb housin
`dichroic filter. The} dichroic ffilter is adap%ed to transmit
`e ectromagnetic ra iation in t e excitation requency and
`of the fluorescent material and reflect electromagnetic radia-
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`5 Claims, 2 Drawing Sheets
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`[54]
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`INSPECTION LAMP WITH THIN-FILM
`_1)1cHR()1(; FILTER
`
`[75]
`
`Inventors: Gustavo Garcia, Lake Grove; John T.
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`[73] Assigncc: Spectmnm Corporationywestbury’
`NY
`[21] Appl‘ NO’: 08/844,741
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`[58] Fleld Of Search ................................... .. 250/301, 302,
`250/504 R: 504 Ha 4931
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`References Cited
`U_S' PATENT DOCUMENTS
`'
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`§‘”“°t5 -----------------------------------
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`1/1973 Wesflund at M‘
`. 362/293
`1/1980 Moretetal.
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`3/1980 Woog
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`5/1981 Moret ........................................ 128/23
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`$711,700
`4,184,196
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`U.S. Patent
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`May 18,1999
`
`' Sheet 1 of2
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`5,905,268
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`1 F
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`IG.
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`

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`U.S. Patent
`
`May 18,1999
`
`Sheet 2 of 2
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`5,905,268
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`5,905,268
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`2
`specific wavelengths, while reflecting those which are unde-
`sirable. By reflecting undesirable visible light, and transmit-
`ting invisible UV light, such a filter can simultaneously
`maximize a desired transmittance while greatly reducing
`thermal stress on the filter. A lamp must also be safe to the
`user and constructed to withstand the rough handling to
`which it may be exposed. An inspection lamp is also needed
`that permits the easy substitution of customized filters for
`difiering applications.
`SUMMARY OF THE INVENTION
`
`An inspection lamp for detection of a fluorescent material
`which absorbs electromagnetic energy in a specific excita-
`tion frequency band and which emits electromagnetic
`energy in a specific fluorescent emission frequency band
`within the visible light spectrum. The lamp includes a bulb
`housing, a light source within the bulb housing, and a
`dichroic filter. The dichroic filter is adapted to transmit
`electromagnetic radiation in the excitation frequency band
`of the fluorescent material and reflect electromagnetic radia-
`tion in the fluorescent emission frequency band of the
`material.
`_
`The dichroic filter in the invention may be adapted to
`transmit an excitation frequency band in the ultraviolet and
`visible blue light wavelength range. The dichroic filter may
`also transmit electromagnetic radiation in the infrared and
`longer wavelength range.
`The dichroic filter may also be attached to the lamp by a
`filter holder releasably attachable to the bulb housing.
`
`BRIEF DESCRIPTION OF '1‘ DRAWINGS
`The drawings show a form of the invention which is
`presently preferred; however, the invention is not limited to
`the precise arrangement shown in the drawings.
`FIG. 1 is an exploded View of the full embodiment of the
`invention.
`‘
`FIG. 2 is a graphical illustration of the estimated percent-
`age of wavelength transmission for a typical filter used in the
`invention compared to colored glass filters currently avail-
`able.
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`DETAILED DESCRIPTION OF THE
`INVENTION
`
`1
`INSPECTION LAMP WITH THIN-FILM
`DICHROIC FILTER
`
`FIELD OF THE INVENTION
`
`This invention is related to the general field of inspection
`lamps for detection of fluorescent materials, and in particular
`to the field of selective filters for such inspection lamps.
`BACKGROUND OF THE INVENTION
`
`Leak detection, materials detection, and qualitative non-
`destructive testing are well suited to techniques employing
`fluorescence detection. These techniques rely upon the
`unique physical property of various materials to fluoresce
`when excited by certain wavelengths of visible or ultraviolet
`'(“UV") light.
`~
`It
`is a well-known phenomena that electromagnetic
`energy within the near ultraviolet spectrum of approximately
`315 to 400 nanometer wavelengths produces fluorescence in
`certain materials. That is, the fluorescent materials absorb
`radiated energy at the near UV or blue wavelengths and
`re—radiate or emit it at a longer wavelength in the visible
`spectrum. Thus, when fluorescent material absorbs electro-
`magnetic energy in a specific excitation frequency band in a
`specific wavelength range, the material can emit electro-
`magnetic energy in a characteristic fluorescent emission
`frequency band within the visible light spectrum. This
`phenomena has enabled inspection and detection techniques
`in which fluorescent dyes, inks or pigments are illuminated
`by lamps selectively filtered to emit only ultraviolet radia-
`tion (invisible to the human eye), and then re-radiate with a
`high luminescence in the visible spectrum.
`For example, the slow leakage of refrigerant from an air
`conditioning system is difiiicult to locate by any other means,
`because the refrigerant escapes as an invisible gas at such
`low rate and rapid diffusion that the concentration of refrig-
`erant in air near the leak site is difficult to differentiate from
`that surrounding any other location along the system circu-
`lation lines. However, by infusing into the circulating system
`a small amount of fluorescent dye which is soluble in the
`refrigerant, the dye is carried out of the system with the
`refrigerant, and glows brightly at the leak site when the area
`is swept with a UV lamp.
`Currently available inspection lamps employ high inten-
`sity light sources operating at very high temperatures to
`generate a sufiicient photon flux for detection applications,
`and utilize filters to absorb the undesirable wavelengths.
`These filters are often colored glass which transmit some
`wavelengths and absorb others. The filters are subjected to
`significant thermal stress attributed to the high temperature
`light source and the filter’s absorption of light energy.
`Because of the thermal stress problem,
`the selection of
`appropriate materials for a filter are limited. The colored
`glass filters that are commonly used do not optimize the
`transmittance of the desirably narrow ultraviolet frequency
`bandwidth needed to maximize the fluorescence of a par-
`ticular material.
`.
`Another problem with currently available inspection
`lamps is the tendency for UV colored glass filters to permit
`transmittance of lower wavelength visible light. These
`wavelengths interfere with the human eye’s perception of
`light emitted from the fiuorescing material. This is a sig-
`nificant limitation in applications where fluorescing material
`is expected in low concentrations, as in the refrigerant leak
`example.
`Thus, there is a need for an inspection lamp that utilizes
`a high intensity light source and a filter which will transmit
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`The present invention may be embodied in other specific
`forms without departing from the spirit or essential attributes
`thereof and, accordingly, reference should be made to the
`appended claims, rather than to the foregoing specification,
`as indicating the scope of the invention.
`A hand-held ultraviolet wavelength inspection lamp that
`optimizes the fluorescent response of a material and miti-
`' gates the thermal stress on a filter, thus enabling a more
`versatile and durable inspection device, is made feasible by
`the use of an optical th/in-film coated dichroic filter.
`FIG. 1 depicts an inspection lamp 10 of the present
`invention. A lamp casing 12 is attached to a handle 14. The
`handle 14 enables the inspection lamp 10 to be a portable,
`hand-held device. The dimensions of the inspection lamp 10,
`and ‘in particular those of the lamp casing 12 and handle 14,
`are chosen to enable ease of use. The handle 14 may be
`provided means for enhancing a hand-held grip, such as a
`rubber material, or be ergonomically formed to emulate the
`contours of a gripped hand.
`In one embodiment of the invention, the lamp casing 12
`and handle 14 may share the same principle longitudinal
`axis. In such an embodiment, the inspection lamp 10 has an
`in-line, or “flashlight”appearance.
`
`

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`5,905,268
`
`3
`An on/off switch 16 is positioned on the handle 14. In a
`preferred embodiment, the on/off switch 16 is a push—button.
`A bulb 18 is positioned within the lamp casing 12. The
`bulb 18 is a high intensity light source, enabling a maximum
`fluorescent response from a subject material. The bulb 18 is
`a source for a broad range of wavelengths,
`including
`ultraviolet, visible, and infra-red. The bulb 18 may be a
`commercially available mercury vapor, xenon, metal halide,
`or halogen bulb. In fact, any bulb that can provide the
`necessary light intensity and broad range of wavelengths is
`sulficient. The bulb 18 is joined to a two-pin bulb socket 20.
`The two-pin bulb socket 20 is mounted in a socket bracket
`22.
`
`The bulb 18 is positioned within a bulb housing 24, both
`within the lamp casing 12. The bulb 18 is secured to the bulb
`housing 24 by fastening the socket bracket 22 to a housing
`bracket 30 on the bulb housing 24. This may be accom-
`plished with the use of screws (not shown). The bulb
`housing 24 has an open end opposite the housing bracket 30.
`The bulb housing 24 has a conical section 28 having a form
`selected for focusing light emitted from the bulb 18. An
`extended reflector housing 32 extends from the conical
`section 28. A reflector surface 26 internally lines the bulb
`housing 24 along the conical section 28 and the extended
`reflector housing 32. The bulb 18 is mounted within the bulb
`housing 24 such that the light source essentially encom-
`passes the focus or foci of the reflector 26. The contour of
`the reflector 26 is selected to produce a close-in convergence
`of the emitted light. Thus, light emitted from the bulb 18 is
`concentrated and transmitted towards the open end of the
`bulb housing 24. Light is ultimately transmitted through the
`aperture 38 of the lamp casing 12. The focal characteristics
`of the bulb housing 24 and the reflector 26 can be selected
`to focus the transmitted light beam so as to converge at a
`distance from the lamp or to promote a better flood beam.
`The ‘open end of the bulb housing is adapted to receive a
`filter holder 34. In a preferred embodiment, the filter holder
`34 is releasably attachable to the bulb housing 24. The filter
`holder 34 houses a filter 36. The filter of the present
`invention is an optical thin-film coated UV dichroic filter.
`Dichroic filters are constructed to selectively reflect
`undesired light frequencies while transmitting desired fre-
`quencies. These filters operate by having multiple thin films
`or coatings applied to a surface of a filter material. The
`thickness of these coatings can be controlled to the point
`where they are applied in increments of one-quarter or
`one-half the wavelength of specific light colors. When these
`layers are applied in materials of differing refractive indices,
`the transmission or the refiection of specific wavelengths of
`light can be closely controlled. Thus, a filter can be designed
`to transmit specific wavelengths and reflect those which are
`undesirable. There is minimal absorption of light by the
`filter.
`
`Adichroic filter for an inspection lamp can be designed to
`optimize the transmission of UV and blue light, and is
`superior to the performance of colored glass filters designed
`for the same purpose. An example of the transmission
`characteristics of a filter that may be employed in the
`invention is shown in FIG. 2. The dichroic filter has a higher
`percentage (approximately 90%) of transmittance of near
`ultraviolet (300—~380 ‘nm) and violet (380—400 nm) radiation
`than comparable colored glass filters. Even more significant
`is the sharp drop-off of transmittance around the 400-420
`nm band compared to the long slope of the transmittance
`drop-off for the colored glass filters. Thus, the dichroic filter
`can maximize the transmission of the ultraviolet bandwidth
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`Which provides the excitation energy to cause a material to
`fluoresce, while reflecting the visible light in the fluorescent
`emission frequency band which would tend to mask the
`fluorescent
`radiation. The dichroic filter can thus be
`designed to have a transmission curve which has high
`transmittance for the excitation frequencies and almost no
`transmittance of the fluorescing frequencies of common,
`commercially available dyes used for fluorescent inspection,
`such as perylenes and naphthalirnides. The materials then
`appear more brilliantly as indicators of leaks or other
`inspection conditions.
`A dichroic filter 36 with UV and blue transmission
`characteristics similar to that shown in FIG. 2 is available as
`the B 46 Dichrolight filter and manufactured by Balzers AG
`in Liechtenstein. Bausch & Lomb and other companies
`likewise produce satisfactorydichroic filters for use in this
`invention.
`
`The transmission curve of a resulting filter can be shifted
`by as much as 10 nm, towards longer or shorter wavelengths,
`by careful alteration of the coating process. Moreover, the
`construction of an appropriate filter may utilize a glass
`substrate. _Because a customized transmission profile is
`possible, hybrid filters having thin-film coatings applied to
`an existing colored glass filter can be manufactured.
`As also shown in FIG. 2, a dichroic filter can be designed
`to simultaneously transmit infra-red wavelengths. This is
`advantageous because the otherwise absorption or reflection
`of infra-red wavelengths results in thermal stress to the filter
`or bulb housing. Infra-red wavelengths do not interfere with
`a fluorescing dye’s visible transmission. Thus, a dichroic
`filter can be designed to further facilitate heat transfer from
`the bulb housing.
`The fact that specific portions of light can be selectively
`controlled provides significant benefits when applied to
`filters incorporated in inspection lamps which are used to
`fluoresce materials during inspection processes. The base
`material onto which the films are deposited is no longer
`limited to those which can" resist
`the thermal stresses
`incurred when they absorb the undesirable light wave-
`lengths. Therefore, more options are available in base
`materials, and the benefits which can be derived from the
`mechanical properties of materials which would otherwise
`be unusable would be available. These dichroic selective
`filters can also be employed as layers of filters to create a
`filter stack which could further refine the resulting light
`transmission.
`'
`There are numerous applications for an inspection lamp of
`the present invention. Several commercially available dyes
`used in leak detection applications fluoresce after being
`excited by ultraviolet and visible blue wavelengths. As noted
`above, the fluorescent response of these dyes can be maxi-
`mized by selective filtering of the light transmission used to
`excite the dye molecules. The resulting light transmission
`would be much more intense and the total amount of light
`energy available to fiuoresce a material
`is significantly
`greater, thus increasing the probability that a dye molecule
`will fluoresce and be observed, and a weakness in a pipe or
`conduit detected.
`
`Because many materials are known to naturally fluoresce,
`a hand-held inspection lamp may be used for materials
`detection. Certain types of fungus or minerals are examples
`of materials whose detection would be much more effi-
`ciently achieved with an inspection lamp that can transmit
`specific wavelengths of electromagnetic radiation character-
`istic to those materials. Customized dichroic filters used in
`the inspection lamp of the present
`invention make this
`possible.
`
`

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`5,905,268
`
`5
`Non-Destructive Testing techniques require UV inspec-
`tion of subject components treated with a fluorescent mate-
`rial. These applications often require the maximum exclu-
`sion of Visible light possible. The inspection lamp of the
`present invention can ensure that a maximum amount of a
`very small band of UV light is transmitted to the exclusion
`of interfering visible light.
`While the present invention has been described in con-
`nection with various preferred embodiments thereof, it will
`be appreciated that it should not be construed to be limited
`thereby. Modifications remain possible, without departing
`from the scope and spirit of the appended claims.
`We claim:
`1. An inspection lamp for detection of a fluorescent
`matcrialwhich absorbs electromagnetic energy in a specific
`excitation frequency band and which emits electromagnetic
`energy in 21 specific fluorescent emission frequency band
`I within the visible light spectrum, the lamp comprising:
`a) a bulb housing;
`b) a high intensity light source within the bulb housing;
`
`6
`c) a dichroic filter adapted to transmit electromagnetic
`radiation in the excitation frequency band and in the
`infrared and longer wavelength region, and to reflect
`electromagnetic radiation in the fluorescent emission
`frequency band.
`2. An inspection lamp as in claim 1, wherein the excitation
`frequency band is in the ultraviolet and Visible blue light
`wavelengths.
`3. An inspection lamp as in claim 2, wherein the excitation
`frequency band is in the wavelength range of about 360 nm
`to about 470 nm.
`’ 4. An inspection lamp as in claim 2, wherein the dichroic
`filter transmits about 90 percent of the electromagnetic
`energy having a wavelength in the range of about 300 nm to
`about 380 nm.
`
`5. An inspection lamp as in any one of claims 1 through
`4, further comprising the dichroic filter being attached to the
`lamp by a filter holder releasably attachable to the bulb
`housing.
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