Scalar irradiance meter

An apparatus for measuring scalar irradiance or the incident flux of radiant energy from a 4.pi. solid angle about a point. The present invention relates to an apparatus which comprises a solid spherical radiant energy collector, a radiant energy detector which converts radiant energy into electrical signal, a light conductor which transmits a portion of the radiant energy within the spherical collector to the detector, a means for conditioning the electrical signal such that the electrical signal responds to the intensity of the incident flux, and a means for displaying the conditioned signal. The apparatus further includes a spectral shaping assembly located intermediate the detector and the light conductor whereby the spectral characteristics of the radiant energy are adjusted to compensate for apparatus response in the desired spectral region.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
This invention relates to a new and unique apparatus for measuring scalar 
irradiance with variations adapted to measure the incident flux of a 
continuous 4.pi. or 2.pi. solid angle in a laboratory or underwater 
environment. 
Devices of this type detect and measure the intensity of radiant energy to 
establish the total radiation available for photosynthesis and for a 
variety of other related biological examinations. The device which 
provides such intensity measurements should be suitable for underwater 
operation, easy to manipulate, provide measurements in standardized 
physical units, be spherically responsive to a continuous 4.pi. incident 
flux, and respond selectively to photosynthetically significant energy. 
BRIEF DESCRIPTION OF THE PRIOR ART 
A number of devices are available which measure radiant flux, however, 
these devices exhibit spectral and spatial response characteristics which 
are inconsistent with and irrelevant to present photosynthetic studies. 
Light measuring devices are characterized as being "photometric" or 
"radiometric". Photometric relates to the determination of the intensity 
of the light field by a device which exhibits a spectral or frequency 
response that is similar to that of the human eye. Radiometric relates to 
the determination of the intensity of the light field by a device that 
responds to physical parameters of the light such as the amount of energy 
within a given frequency range. 
The article Photon Scalar Irradiance, Smith and Wilson, Applied Optics, 
Volume II, Page 934, April 1972, describes one form of a radiometric 
device which is designed to measure scalar irradiance. The Smith and 
Wilson device employs two opposed fish-eye lenses to focus hemispherical 
light onto a light detector. The Smith and Wilson device, however, 
demonstrates an appreciable reduction in sensitivity at the horizon of 
each hemisphere. Further, the Smith and Wilson device requires extensive 
optical components. 
The article entitled A 4.pi. Light Meter, Maddux, Limnology and 
Oceanography, Volume 2, pages 136-137, 1966, describes a device which 
imbeds a light detector into a plastic or styrofoam sphere. This device 
also prohibits the spectral and spacial characteristics of the incident 
light flux to be shaped, and it has reduced operating flexibility because 
of the juxtaposition of the styrofoam collecting sphere and the light 
detector. 
Other devices propose the hemispherical collection of light with electronic 
detection but exhibit reduced sensitivity at the horizon and reduced 
flexibility for spectral shaping. For example, the device disclosed in A 
Simple Sensitive Underwater Photometer, Rich & Wetzel, Limnology and 
Oceanography, Volume 14, pages 611-613, 1969, is bulky and inappropriate 
for experimental laboratory work. 
Scalar Irradiance as a Parameter in Phyloplankton Photosynthesis and a 
Proposed Method for its Measurement, Currie, Radiant Energy in the Sea, 
International Association of Physical Oceanography, pages 107-122, 1960, 
discloses a device with two hemispherical cosine type collectors which 
exhibit considerable reduced sensitivity at the horizon. Similarly, A 
4.pi. Underwater Irradiance Meter, Sasaki, Oshibico, and Kishino, Journal 
of the Oceanographical Society of Japan, Volume 27, No. 4, pages 123-128, 
August 1966, shows a device with hemispherical lense but with a cosine 
type detector which results in the reduced sensitivity at the horizon. 
U.S. Pat. No. 3,180,210 describes still another example of a device to 
measure scalar irradiance using a hollow diffusing sphere with rotating 
mirrors and phototubes. This device is cumbersome, subject to depth 
limitation and generally impractical for laboratory work. 
Further, none of these devices describe a device which incorporates 
electrical signal conditioning to enable a direct readout in light 
measurement units appropriate for instantaneous or integrated scale 
irradiance determination, nor are these devices readily adaptable to both 
field and laboratory use. 
SUMMARY OF THE INVENTION 
The present invention relates to an apparatus for measuring scalar 
irradiance. The devices defined by this invention measures the intensity 
of light flux incident upon a sphere from a 4.pi. solid angle about the 
center of the sphere. 
The apparatus disclosed in this invention comprises a solid spherical light 
collector whereby light which strikes the outside of the sphere becomes 
increasingly diffused as it penetrates the sphere. A light conductor 
transmits a proportion of the light within the sphere to a spectral 
shaping device. The spectral shaping device is a series of lenses and 
filters which partially collimate the diverging light exiting the light 
conductor and adjusts the spectral characteristics of the light to 
compensate for anomolies in the apparatus and for the denied unit of light 
measurement. An electronic conditioning device with a light detector 
detects the light intensity and converts it into an electronic signal, 
then adjusts and manipulates the electronic signal for its display on an 
appropriate light intensity readout device. 
An object of the present invention is to provide an apparatus for measuring 
scalar irradiance. A further object of the present invention is to provide 
an apparatus for measuring scalar irradiance in units of photon flux or 
energy flux in either an instantaneous or integrated mode. A further 
object of this device is to provide a device which can be adapted to 
provide a substantially spherical response to both a 2.pi. and 4.pi. 
incident light flux. 
An object of the present invention is to provide an apparatus for measuring 
scalar irradiance which has the ability to interchange frequency or 
wavelength spectral shaping filter whereby the apparatus is optically 
tuned to the units of measure. A further object of the present invention 
is to provide an apparatus for measuring scalar irradiance whereby the 
light collecting device is remote relative to the light conversion means. 
A further object of the present invention is to provide an apparatus for 
measuring scalar irradiance which includes an electrical signal 
conditioning device which may be remote to the detector and which may be 
remote to the readout device.

DESCRIPTION OF THE PREFERRED EMBODIMENT cl Primary Embodiment 
FIG. 1 shows a preferred embodiment of the scalar irradiance meter which is 
adapted to hand-held operations in a laboratory environment and can be 
further adapted for use in an underwater environment. Specifically, this 
embodiment called the first meter, shown generally as 11, includes a solid 
spherical collector 12, a light conductor 13, an optical housing 14 which 
encloses the spectral shaping device, an electronic housing 15 which 
encloses the electronic conditioning device, and readout devices 16. 
The solid spherical collector 12 increasingly diffuses light which strikes 
the spherical collector 12 as it penetrates the spherical collector 12. 
Any diffusing material such as styrofoam would be appropriate; however, 
teflon is preferred due to its mechanical properties which make it easily 
machinable. While a wide range of spherical dimensions are acceptable a 
collector 12 with a spherical diameter of between 0.50 inches and 1.50 
inches is preferred. 
The light conductor 13 may be fabricated out of any light transparent 
material. Examples include: glass rods, quartz rods, glass fiber bundles, 
and plexiglass rods. The embodiment shown in FIG. 1 employs a glass fiber 
bundle 13 as provided by Americal Optical and designated as ULGM-2-12. 
Both the forward ends 31 and the rear ends 32 of the light conductor 13 
are dipped in a suitable epoxy and inserted into respective forward end 
cap 33 and rear end cap 34. The outer ends of each end cap 33 and 34 are 
ground flat and smooth for best light transmitting results. 
The solid spherical collector 12 is prepared with a receiving hole 21 into 
which the forward end cap 33 is inserted. The interior diameter of 
receiving hole 21 is slightly smaller than the exterior diameter of 
forward end cap 33, whereby the insertion causes slight deformation of the 
hole 21. The subsequent relaxation of the deformed teflon around the hole 
21, securely retains the inserted forward end cap 33. 
The preferred glass fiber bundles light conductor 13 is further provided 
with a protective flexibly coiled steel shield 35 and a protective forward 
seal cap 37. The rear end cap 34 of the rear end 32 of the conductor 13 is 
inserted into a rear seal cap 38 mounted to the upper end plate 41 of the 
optical housing 14. 
The optical housing 14 is a cylindrical chamber adapted to enclose the 
spectral shaping device, shown generally as 42. The spectral shaping 
device 42 includes a series of collimating convex lenses 43 and 
subtractive color or spectrum filters 44. The nature of the lenses 43 and 
their placement is designed to focus the light exiting the conductor 13 on 
a light detector 51 mounted to the lower end plate 36 of the optical 
housing 14. The spectrum filters 44 are designed to adjustments in the 
wavelength or frequency characteristics of the light meter 11, whereby 
direct readouts of the light intensity in preselected units, such as 
numbers of photons or amount of energy, is possible. 
Specifically, the spectrum filters 44 are selected to adjust the frequency 
response of light meter 11 such as that shown in FIG. 2. FIG. 2 depicts 
the relative quantum response along the vertical axis and the wavelength 
of the incident light along the horizontal axis. The horizontal wavelength 
scale shows a range of approximately 350 to 700 nanometers, the generally 
accepted range of useful light in photosynthetically significant 
experiments. The frequency spectrum indicated at A depicts an ideal 
quantum response for an equal number of photons for each frequency. The 
frequency spectrum indicated at B depicts the energy response for an equal 
amount of energy at each frequency. The frequency spectrum indicated at C 
depicts the characteristic response of the human eye. The frequency 
spectrum indicated at D depicts the shape of an ideal narrow wavelength 
meter. 
By appropriate selection of the spectrum filters 44, the characteristic 
response of the light meter 11 can be adapted to any of those shown in 
FIG. 2. Other spectrum response characteristics can be established where 
appropriate. 
Referring back to FIG. 1, the light detector 51 is a conventional photo 
cell which converts light energy into electrical energy; whereby the 
greater the intensity of light striking the face 51C of the detector 51 
the greater the current generated at terminals 51A and 51B. The detector 
51 and the spectral shaping device 42 are adjustably attached through a 
spring and screw device 45 in the secured lower end plate 36 such that the 
collimated light is focused directly on the face 51C of the detector 51. 
The terminals 51A and 51B are connected to voltage amplifiers 71 (FIG. 3) 
within the electronic housing 15. While the electronic housing 15 may be 
located within the same enclosure as the optical housing 14 the embodiment 
described herein shows a light meter 11 which has the electronic housing 
15 located remote relative to the optical housing 14. 
The detector 15 is connected to the amplifier 71 (FIG. 3) through 
conventional connection devices as shown in FIG. 1, namely an input pair 
of BNC connectors 53 mounted on the optical housing 14, a co-axial cable 
54 and an output pair of BNC connectors 55 mounted on the electronic 
housing 15. 
The electronic conditioning circuitry, shown generally as 57, is 
schematically presented in FIG. 3. In FIG. 3 the detector signal is 
provided as the center contact 55A of connector 55 and is connected to 
amplifier 71 (AMP) through line 61, the other contact 55B being chassis 
grounded. An amplifier suitable for this application is the Intersil ICH 
8500A configured as a current-to-voltage converter. The current-to-voltage 
ratio is determined by the feedback network 56 connected between the 
amplifier input 71A by line 62 and the amplifier output 71B by line 63. 
The feedback network 56 (FED) includes an adjustable intensity range 
switch 57A whereby the current-to-voltage ratio is adjusted to match 
significant fluctuations in the intensity of the light field. Conventional 
range changing and high frequency roll-off procedures are used in the 
feedback network 56. 
The amplifier output 71B is further connected via line 64 to a panel 
voltage meter 58 (VMTR) for displaying the instantaneous light field 
intensity. The amplifier output 71B is also connected to output jack 59 
via line 65 to drive a variety of voltage sensitive recording devices 16 
(FIG. 1). 
The amplifier output 71B is further connected via line 66 to the voltage 
input terminal 74A of a voltage-to-frequency converter 74 (VFC). A nominal 
0 to 5 volt D.C. source is proportionally converted to a 0 to 1 KH 
frequency. The frequency output terminal 74B of the voltage-to-frequency 
converter is conventionally connected, via line 67, to the serial input 
75A of a series of two 4-digit decade counters 75 (DCT), such as National 
Semiconductor MM 74 C926N. 
The decade counter 75 accumulates a count of the frequency over a specified 
time. The larger the light intensity, the greater the voltage, the higher 
the frequency, and the larger the count. The range switch 57A is also 
connected via line 70 to the decade counter 75 to provide an accumulator 
rate which corresponds to the range switch 57A setting. 
A timing circuit 76 (TC) is connected to the decade counter 75 via line 68 
which enables the counter to accumulate a count for a fixed predetermined 
period of time. Manual control of the timing circuit 76 enables selection 
of short duration, long duration or continuous count accumulations. 
The digital output 75B of the decade counter 75 is conventionally connected 
via lines 69 to an 8-digit digital readout display 77 (ROUT). A 
satisfactory display drive is a 5-digit, 7-segment, light-emitting diode 
display. Digital drivers 78 (DDR) are connected, via lines 79 to the 
digital readout display 77 to supply the required display drive current. 
The drivers 78 are manually controlled, whereby the readout display 77 may 
be turned on and off to conserve the power source 72 (PSR). 
Power to the electronic circuitry is conventionally provided by power 
source batteries 72. Power switch 73 enables and disables the power source 
72. 
In the embodiment shown in FIG. 1, the power source 72 is a stack of 
rechargeable nickel-cadmium batteries with output arranged to deliver the 
necessary power, such as +8.25 Vdc, -7.5 Vdc, +5.00 Vdc and 0.0 Vdc. The 
power source 72 may be alternatively provided as a conventional power 
supply operating on a standard 110 ac current. 
Referring back to FIG. 1, the voltage sensitive recording device 16 may 
consist of any recording device responsive to a varying input voltage 
signal. For example, a digital voltage level recorder and strip chart 
recorder. These are suggested as examples only and not intended to limit 
either the scope or essence of this invention. 
A wide variety of electronic conditioning circuitry can be developed and 
the examples presented herein are presented for demonstration purposes 
only. The particular embodiment presented is not intended to limit or 
restrict the essence of this invention. Alternative electronic circuitry, 
which can be employed, to provide relevant information on the measurement 
of light intensity, includes maximum or minimum threshold counting 
devices, average intensity recorders, and integrated intensity recording 
devices. 
In operation the solid spherical collector 12 presents substantially a 
spherical cross-section to incident light from all directions. 
Additionally, the placement of the light detector 51 apart from the 
collector 12 allows the easily adjustable, removable and replaceable 
spectral shaping device 42. Significantly, the light conductor 13 provides 
the freedom to locate the collector 12 apart from the detector 51, thereby 
preventing disruption of the light environment. 
Including the electronic conditioning circuitry 57, the instantaneous light 
intensity voltage meter 58, and the integrated light intensity digital 
display 77 within the light meter 11 produces a light metering apparatus 
which has never been seen in the prior art. 
In practice, the light meter 11 is turned on via power switch 73, the 
timing circuit in 76 is set, and the display drivers 78 are turned on 
enabling the digital display 77. Any attached recording devices 16 are 
similarly enabled. The solid spherical collector 12 of the light meter 11 
is placed within the light field in question. The light penetrating the 
collector 12 is diffused, such that the light in the vicinity of the 
center of the collector 12 has undergone sufficient scattering so as to 
have lost its directional nature. A proportional quantity of incident 
light enters the light conductor 13 through its polished forward end 31. 
The light is then channeled through the conductor 13 to the spectral 
shaping device 42. There the light is appropriately filtered and focused 
onto the detector 51. 
The electrical signal generated by the detector 51 is transmitted to the 
electronic circuitry 57. The electrical signal is appropriately 
conditioned and presented for readout on the voltage meter 58. The 
electrical signal is further conditioned whereby an accumulated count is 
displayed on the digital display 77. The conditioned voltage is also 
provided at the output jack 59 for use by recording devices 16. The 
displayed readings are calibrated and the intensity of the light field 
thus determined. 
First Alternate Embodiment 
FIG. 4 shows the First Alternative embodiment of the light meter, 
designated hereinafter as the complete meter and generally referred to as 
111. The complete meter 111 is designed to be completely self-contained 
and to operate in an underwater environment. The complete meter 111 is 
functionally and operationally similar to the light meter 11 shown in FIG. 
1. 
The complete meter 111 includes a solid spherical collector 112, a light 
conductor 113, an optical housing 114, an electronic housing 115, and 
optional recording devices (not shown). 
The solid spherical collector 112 is substantially the same as the 
collector 12 described above (see FIG. 1). However, the light conductor 
113 is made out of an alternative material, solid clad quartz rod. The 
forward end 131 of the quartz conductor 113 is polished and inserted into 
a hole 121 within the collector 113. The rear end 132 of the quartz 
conductor is inserted through a watertight seal 134 in the forward end 141 
of the optical housing 114. 
The optical housing 114 and the electronic housing 115, in this embodiment, 
are fabricated as a single integrated watertight enclosure 117. However, 
for purposes of comparison, this discussion will refer to that portion of 
the watertight enclosure 117 which houses the spectral shaping device 142 
as the optical housing 114, and that portion which houses the electronic 
conditioning circuitry 157 as the electronic housing 115. 
Within the electronic housing 115 an electronic circuit 157, similar to 
that described above and shown in FIG. 3, is included. In the complete 
meter 111, however, a watertight power switch 173, a watertight voltage 
meter 158, and a watertight digital display 177 are provided. The manner 
in which these devices are made watertight is not considered substantive 
to this invention. A watertight output jack 159 is also provided so that 
the remote light recorded measurements taken with the complete meter 111. 
The spectral shaping device 142 of the complete meter 111 is analogous to 
spectral shaping device 42 within the light meter 11; however, the 
electronic conditioning circuitry 157 is adapted to fit within the 
complete meter 111. The electronic conditioning circuitry 157, which is 
schematically the same as the electronic conditioning circuitry 57 of the 
light meter 11, shown in FIG. 3, is mounted on a printed circuit card 145 
which is adapted to fit within the electronic housing 115. Similarly the 
power source 172 and the power switch 173, voltage meter 158, and digital 
display 177 are adapted to fit within the electronic housing 115. 
The operation of the complete meter 111 is analogous to that of the light 
meter 11. The collecting sphere 112 is placed within the light field in 
question and the complete meter 111 turned on. A proportional amount of 
light penetrating the spherical collector 112 is transmitted through the 
light conductor 113 to the spectral shaping device 142, where the light is 
filtered and focused on the detector 151. The electronic conditioning 
circuit 157 then conditions the electrical signal produced by the detector 
151 for display. The instantaneous light intensity can be determined by 
reading the voltage level meter 158, the integrated light intensity can be 
determined by reading the digital display 177. 
Second Alternate Embodiment 
The second alternate embodiment of the invention, a hemispherical meter, 
shown in FIG. 5 and designated generally as 211, is designed to measure 
the scalar irradiance from a restricted continuous 2.pi. hemisphere. The 
hemispherical meter, 211, consists of essentially the same basic 
components as included in the light meter 11; namely, a solid spherical 
collector 212, a light conductor 213, an optical housing 214, a remote 
electronic housing (not shown), and optional recording devices (not 
shown). Significantly, the hemispherical meter 211 also includes a 
hemispherical shield 218. 
Because the structure of the hemispherical meter 212 is functionally and 
operationally analogous to the structure of the light meter 11, shown in 
FIG. 1 and described above, only the function and operation of the 
additional structure of the hemispherical meter 211 is presented. The 
purpose of the hemispherical meter 211 is to measure the scalar irradiance 
incident on a point from a continuous 2.pi. hemisphere. The response of 
the hemispherical meter 211 resulting from a light source directly in 
front of the meter is substantially the same as its response of the same 
light source just above the horizon and provides no response just below 
the horizon. 
The solid spherical collector 212 of the hemispherical meter 211 is 
centered above a hemispherical shield 218. The shield 218 is a flat 
circular plate 281 with a nominally one inch high perpendicular lip 282 
circumventing the plate 281. 
The solid spherical collector 212 is mounted on the light conductor 213 in 
the center of the circular plate 218. The optical housing 214 is mounted 
behind the circular plate 218 with the electrical housing being remotely 
located. 
The orientation of the upper edge 283 of the lip 282 relative to the 
spherical collector 212 is such that the equatorial circumference 284 of 
the spherical collector 212 is substantially within the same plane as that 
plane described by the upper edge 283 of the lip 282. This configuration 
enables substantially the entire continuous 2.pi. hemisphere to "see" a 
spherical collector. Only a slight angle .phi. above the horizon is unable 
to see a complete spherical collector; the tangent of the angle .phi. 
being given as the ratio of the diameter of the spherical collector to the 
diameter of the circular plate. For a small angle .phi., the diameter of 
the circular plate 281 must be large relative to the diameter of the 
spherical collector 212. 
The circular plate 281 and lip 282 are coated with a light absorptive 
material which prevents reflections from the plate 281 to the collector 
212. Such reflections would significantly reduce the accuracy of the 
hemispherical meter 211. 
The hemispherical meter 211 is typically operated in the vertical position 
thereby measuring the 2.pi. scalar irradiance from the sun and sky above. 
In all other aspects the application of and operation of the hemispherical 
meter 211 is similar to the light meter 11. 
Third Alternate Embodiment 
The third alternate embodiment is a dual hemispherical meter, shown 
generally as 311 in FIG. 6. The dual meter 311 is a watertight light meter 
designed to measure light intensities from opposite horizontal hemispheres 
(that hemisphere whereby the normal to the plane of its horizon is 
horizontal). While the components of the dual meter 311 are analogous to 
the light meter 11 shown in FIG. 1, the dual meter includes two 
hemispherical type meters, similar to that of the hemispherical meter 211 
shown in FIG. 4. 
The dual meter 311 consists of two opposed solid spherical collectors 312A 
and 312B, respectively, in the center of corresponding hemispherical 
shields 318A and 318B, respectively. The operation of each of the separate 
horizontal hemispherical detectors, shown generally as 311A and 311B, 
respectively, is analogous to that of the hemispherical meter 211. The 
separate horizontal hemispherical detectors, 311A and 311B, respectively, 
are located in opposite ends 319A and 319B, respectively, of a cylindrical 
chamber 319. 
The light conductors, 313A and 313B, respectively, transmit proportional 
amounts of light incident upon the corresponding collectors 312A and 312B, 
respectively, to the optical housing 314 located within the chambers 319. 
At the optical housing 314 the separate light conductors 313A and 313B are 
combined into a single conductor 313C which transmits the light to a 
single enclosed spectral shaping device 342. An alternate embodiment of 
the dual meter 311 may provide for separate metering apparatuses for both 
the separate horizontal hemispherical detectors 311A and 311B, 
respectively. 
The spectral shaping device 342 is similar to that of the light meter 11 
shown in FIG. 1. Within the spectral shaping device 342 the light is 
appropriately filtered and focused onto a single detector 351. The 
detector 351 produces an electrical signal which is transmitted to the 
electronic conditioning circuit 357 within the electrical housing 315. 
The electronic conditioning circuit 357 of the dual meter 311 has been 
divided into two portions, a pre-amplifier circuit 357A and a readout 
circuit (not shown). The purpose for this separation is the result of the 
typical use of dual meter 311. Generally, the dual meter 311 is lowered to 
some depth in the ocean requiring the display device to be located 
remotely, on shipboard, and requiring the electrical signal produced by 
the detector 351 to be strengthened by a pre-amplifier so that it can be 
effectively transmitted to the ship. 
The pre-amplifier 357A is of conventional design, as is the remotely 
located (shipboard) readout circuit. The power required to operate the 
pre-amplifier circuit 357A is provided by either batteries housed within 
the chamber 319 or by shipboard power provided through a support and data 
cable (not shown). 
The dual meter 311 further includes depth and temperature sensors, 392 and 
393, respectively. The depth sensor 392 and temperature sensor 393 are 
provided with conventional electronic circuitry to enable the display of 
the corresponding measurements. 
Electronic signal produced by light detector 351, and the signal produced 
by the depth sensor 392, and temperature sensor 393 are pre-amplified and 
transmitted from the chamber 319 to the remote (shipboard) readout circuit 
and corresponding display devices, over a multiconductor support and data 
cable. The multi-conductor support and data cable provides the power for 
the pre-amplifier circuit 357A and serves as a support cable for the 
chamber 319. The support cable (not shown) is attached to a bridle 
attachment 391, and is connected to the pre-amplifier circuitry 357A and 
sensor circuitry via connector 353. 
The variety of alternate methods or techniques for producing electronic 
signals to be transmitted to the remote display devices and for 
transmitting those electronic signals are considered within the scope of 
this invention. 
It is to be understood that the description of my invention presented 
herein is done to fully comply with the requirements of 35 U.S.C. 112 and 
is not included to limit or restrict the essence of this invention. 
Variant forms of the apparatus described herein, which employs spherical 
collectors, light conductor, spectral shaping, electronic conditioning and 
readout devices for instantaneous and integrated light intensity 
measurements, could easily be developed. Such variant forms are considered 
within the scope of this invention.