Patent Abstract:
the present invention involves a light system for stimulating or regulating neuroendocrine , circadian , and photoneural systems in mammals based upon the discovery of peak sensitivity ranging from 425 - 505 nm ; a light meter system for quantifying light which stimulates or regulates mammalian circadian , photoneural , and neuroendocrine systems . the present invention also relates to translucent and transparent materials , and lamps or other light sources with or without filters capable of stimulating or regulating neuroendocrine , circadian , and photoneural systems in mammals . additionally , the present invention involves treatment of mammals with a wide variety of disorders or deficits , including light responsive disorders , eating disorders , menstrual cycle disorders , non - specific alerting and performance deficits , hormone - sensitive cancers , and cardiovascular disorders .

Detailed Description:
the science of photobiology involves the study of how the infrared , visible and ultraviolet portions of the electromagnetic spectrum influence biological processes . there are two broad categories of light measurement techniques : radiometric and photometric . each measurement technique has its merits and drawbacks relative to circadian regulation , neuroendocrine regulation and light therapy . radiometry is based exclusively on the physical properties of light — its energy and wavelength . a radiometer measures the radiant power of a light source over a defined range of wavelengths . radiometers can be configured to measure different bandwidths across the electromagnetic spectrum . the wavelengths within the designated bandwidth can be detected equally , or they can be filtered for differential sensitivity across the various wavelengths . in contrast to radiometry , photometry is based on the selective responsiveness of the human visual system . a photometer is simply a radiometer that has filters added to the detector which “ shape ” the detector sensitivity to resemble the luminance ( brightness ) response of the human visual system . thus , photometry is a special branch of radiometry . between individual humans , there are substantial differences in visual responses . the average photopic and scotopic visual functions are defined with reference to the adaptive state of the rod and cone photoreceptors in the human retina . radiometers can be filtered to detect only those relative proportions of wavelengths that comprise the photopic or scotopic visual response . photometers will detect photopic lux or scotopic lux , respectively . specifically defined , lux measures are measures of illuminance — the amount of light , or luminous flux , falling on a surface . one photopic lux is one lumen per square meter ( 1 m / m 2 ). the new metering system is configured to measure a new lighting unit which could be called “ circadian lux ” as opposed to photopic lux or scotopic lux . most investigators have operated from the assumption that light therapy is mediated via a photoreceptive mechanism in the human eye as opposed to a photoreceptive mechanism in the skin or some other part of the body . the data of the present invention demonstrate that the photoreceptive mechanism for the circadian and neuroendocrine system or the photoreceptive mechanism that mediates light therapy is not identical to the photoreceptive system that mediates the sensory capacity of vision . the healthy females ( n = 6 ) and males ( n = 10 ) in this study had a mean ± sem age of 25 . 7 ± 0 . 8 yrs , demonstrated normal color vision as measured by the ishihara and farnsworth munsell d - 100 tests ( mean fm score : 64 . 2 ± 11 . 5 ), had a stable sleeping pattern ( mean wake - up time 7 : 30 am ± 12 min ), and signed an approved irb consent document before participating . each experiment began at midnight when subjects entered a dimly lit room ( 10 lux ). one drop of 0 . 5 % cyclopentolate hcl was placed in each eye to dilate the pupils , and blindfolds were placed over subjects &# 39 ; eyes . subjects remained sitting upright in darkness for 120 min . while still blindfolded and just prior to 2 : 00 am , a blood sample was taken by venipuncture . during light exposure , each subject &# 39 ; s head rested in an ophthalmologic head holder facing a ganzfeld apparatus that provided a concave , patternless , white reflecting surface encompassing the subject &# 39 ; s entire visual field . the subjects were exposed to the light stimulus from 2 : 00 to 3 : 30 am . during this 90 min exposure , subjects sat quietly , kept their eyes open and gazed at a fixed target dot in the center of the ganzfeld dome . subject compliance for keeping their eyes open and the subjects &# 39 ; pupil size were monitored by a miniature video camera . at 3 : 30 am , a second blood sample was taken . each subject was exposed to complete darkness from 2 : 00 to 3 : 30 am on their control night and was tested with at least 6 days between each nighttime exposure . plasma samples were assayed for melatonin by ria . ( rollag , 1976 ). the minimum detection limit of the assay was 0 . 5 - 2 . 0 pg / ml . control samples had 8 % and 14 % intra - assay coefficients of variation . experimental light stimuli were produced by xenon arc lamps ( photon technology int &# 39 ; l , inc ., princeton , n . j .) enclosed in a light - proof chamber and cooled by high - speed fans and water circulation . an exit beam of light from each source was directed by a parabolic reflector , and excess heat in this beam was reduced by a water filter . monochromatic wavelengths ( 10 - 11 nm half - peak bandwidth ) were produced by a grating monochromator and light irradiance was controlled by a manual diaphragm . the resulting light beam was directed into the top area of a ganzfeld dome and reflected evenly off the walls into volunteers &# 39 ; eyes . the entire reflecting surface of the dome was coated with a white surface with a 95 - 99 % reflectance efficiency over the 400 to 760 nm range . routine measurement of the light irradiance ( μw / cm 2 ) was done with a j16 meter with a j6512 irradiance probe ( tektronix , beaverton , oreg .). experimental light stimuli reflected from the ganzfeld domes were measured at volunteers &# 39 ; eye level immediately before and after the 90 min exposure . additional measures were taken each half hour of the exposure to insure stimulus stability and enable intensity readjustment . subjects in the 505 nm series were exposed to intensities ranging from 0 . 011 to 97 μw / cm 2 ( a 3 log unit photon density range of 10 10 to 10 13 photons / cm 2 ). subjects exposed to 555 nm received control or a 15 μw / cm 2 ( 4 . 2 × 10 13 photons / cm 2 ) exposure . two - tailed , students &# 39 ; t tests were used to assess significance of raw melatonin change from 2 : 00 to 3 : 30 am . these data were then converted to % control - adjusted melatonin change scores as described elsewhere . ( gaddy , 1993 ). for the 505 nm data , sets of pre - exposure melatonin values and % control - adjusted melatonin change scores were analyzed with one - way , repeated measures anova . significant differences between groups were assessed with post - hoc scheffe f - tests ; alpha was set at 0 . 05 . for the 505 nm mean % control - adjusted melatonin suppression data , the computer program origin 6 . 0 ( microcal , northampton , mass .) was used to fit a fluence - response curve to a 4 parameter model as described elsewhere ( brainard , 19893 ), and to test for goodness - of - fit of the data by coefficient of correlation . the full 505 nm data complement , from raw melatonin values to a final fluence - response curve , is illustrated in fig1 - 3 . across all nights of testing , there were no significant differences ( f = 0 . 85 ) between sets of pre - exposure melatonin values indicating that plasma levels were consistent across the different study nights . fig1 shows the mean ± sem pre - and post - exposure melatonin values . one - way , repeated measures anova showed a significant effect of light intensity on plasma melatonin % change scores ( f = 17 . 17 , p & lt ; 0 . 0001 ). paired t tests demonstrated that compared to the 0 μw / cm 2 control night , all intensities at or above 5 . 5 μw / cm 2 significantly suppressed melatonin ( p & lt ; 0 . 05 or less ). in contrast , irradiances of 2 . 8 , 1 . 4 and 0 . 011 μw / cm 2 did not suppress melatonin compared to the control night ( scheffe f values : 0 . 97 , 0 . 01 and 0 . 02 , respectively ). as illustrated in fig2 , all melatonin data were converted to control - adjusted % change scores . as with the melatonin % change scores , anova showed a significant effect of light intensity on plasma melatonin % control - adjusted change scores ( f = 13 . 59 , p & lt ; 0 . 0001 ). fig3 illustrates a best fit , sigmoidal fluence - response curve which plots melatonin % control - adjusted scores against stimulus photon density . the specific formula for this curve is included in the figure . subjects exposed to 555 nm received both control ( 0 μw / cm 2 ) and 15 μw / cm 2 ( 4 . 2 × 10 13 photons / cm 2 ) exposures . for the control and light exposure nights , the mean pre - exposure raw melatonin scores were 64 . 4 ± 12 . 5 and 59 . 6 ± 6 . 2 , while the mean post - exposure scores were 62 . 6 ± 10 . 5 and 49 . 1 ± 6 . 0 , respectively . the modest drop in melatonin over the 90 min 555 nm light exposure period was not statistically significant ( t = 1 . 69 , df = 7 , p = 0 . 14 ). for comparison of responses to 505 nm and 555 nm , fig4 illustrates % control - adjusted melatonin suppression relative at equal photon densities across the two wavelengths . these data reveal that 505 nm is significantly stronger than 555 nm in suppressing melatonin ( t = 3 . 04 , df = 14 , p & lt ; 0 . 01 ). the data presented here demonstrate that : 1 ) there is a clear fluence - response relationship between graded light intensities of 505 nm light and melatonin suppression , and 2 ) that 505 nm light is significantly stronger than 555 nm light for suppressing melatonin in healthy , human subjects . previous studies with animals and humans have illustrated fluence - response relationships for melatonin suppression and circadian phase - shifting with exposure to monochromatic light ( podolin , 1987 ; brainard , 1988 ; nelson , 1991 ) as well as white light ( brainard , 1983 ; boivin , 1996 ). a recent study on human subjects suggests that a four parameter curve is optimal for modeling light - induced melatonin suppression and circadian phase shifting . ( zeitzer , 1997 ). that contention matches earlier animal data ( brainard , 1983 ) as well as the 505 nm data reported here . the demonstration that 505 nm light is more potent than 555 nm light for controlling melatonin has important basic science and clinical implications . in humans , it is well - established that higher levels of ocular illumination are required for stimulating the circadian system than for supporting vision . ( lewy , 1980 , nelson , 1991 ; czeisler , 1986 ). consequently , many investigators have considered the three cone photopic visual system to be responsible for stimulating circadian and neuroendocrine responses since this part of the visual system is responsive to “ bright ” daytime levels of illumination . over the past 20 years most of the published literature on human circadian responses to light reports light levels in terms of illuminance ( lux , lumens ) which is a specific measure based on the traditional sensitivity curve of the photopic visual system . the peak wavelength sensitivity of that curve is 555 nm . ( rodieck , 1998 ). indeed , some researchers have argued that their data support the notion that the visual cones are involved in circadian phase - shifting in humans . ( zeitzer , 1997 ). if melatonin regulation is mediated primarily by the three cone photopic visual system , then 555 nm light should be the most potent wavelength for regulating melatonin . the data here do not support this view . on the contrary , 505 nm is significantly stronger , photon for photon , than 555 nm in suppressing melatonin . the clinical implication of this result is that it is not optimum to use photometric values ( lux ) for quantifying light used therapeutically in patients with certain sleep disorders or circadian disruption due to shiftwork or intercontinental jet travel as is the current standard practice . ( 1995 special issue , j biol ). ultimately , these studies open the door for redefining how light should be measured relative to the circadian system . the best circadian measurement system would match the action spectrum for human circadian regulation . that action spectrum would not only elucidate the relative circadian potencies of different wavelengths , but it should help identify the photoreceptor that initiates signals from the retina to the scn . in summary , monochromatic 505 nm light suppressed melatonin in a fluence - response manner , and is approximately four times stronger than a 555 nm stimulus at an equal photon dose for melatonin suppression . these data demonstrate that the three cone system that is believed to mediate human photopic vision is not the primary photoreceptor system to transduce light stimuli for melatonin regulation . action spectra are determined by comparing the number of photons required for the same biological effect at different wavelengths ( lipson , 1994 ; coohill , 1999 ). the melatonin suppression action spectrum described here was formed from fluence - response curves at 8 wavelengths between 440 nm and 600 nm . a within - subjects design was used for each fluence - response curve . for each wavelength studied , a set of 8 volunteers was exposed to a minimum of 8 different light irradiances on separate nights with at least 6 days between exposures . at the completion of that work , it was determined that a probe of sensitivity to monochromatic light below 440 nm was needed . consequently , a group of 8 subjects was exposed to a single night of no light exposure and a single night of exposure to one irradiance of 420 nm light . volunteers who were involved in shift work , planned long distance jet travel before or during the study period , or had irregular sleeping schedules were excluded from this study . the subject drop - out rate was 7 . 9 %. the ethnic distribution of the 72 subjects who completed this study included 55 caucasians , 9 asians , 4 african americans , 3 hispanics and 1 individual of unknown ethnicity . subjects who had a relatively stable daily sleeping pattern , passed a physical exam for general and ocular health , and signed an approved irb consent document were accepted into this study . a total of 37 females and 35 males between 18 - 30 years old ( mean ± sem age = 24 . 5 ± 0 . 3 ) completed the study . the self - reported mean ± se weekday wake - up time among subjects was 7 : 06 am ± 18 min . all subjects were normal on the ishihara and farnsworth munsell d - 100 tests for color vision ( mean ± sem fm score : 51 . 4 ± 4 . 3 ). each experiment began at midnight when subjects entered a dimly lit room ( 10 lux or less ). one drop of 0 . 5 % cyclopentolate hcl was placed in each eye to dilate the subjects &# 39 ; pupils and blindfolds were placed over their eyes . subjects remained sitting upright for 120 minutes and listened to music on headphones or engaged in quiet conversation . while still blindfolded and just prior to 2 : 00 am , a 10 ml blood sample was taken by venipuncture of the antecubital vein . subjects &# 39 ; blindfolds were then removed and the subjects were exposed to the monochromatic light stimulus from 2 : 00 to 3 : 30 am . during light exposure , each subject &# 39 ; s head rested in an ophthalmologic head holder facing a ganzfeld apparatus that provided a concave , patternless reflecting surface encompassing each subject &# 39 ; s entire visual field ( see fig1 ). during this 90 minute exposure , subjects sat quietly , kept their eyes open and gazed at a fixed target dot in the center of the ganzfeld dome . subject compliance for keeping their eyes open and the subjects &# 39 ; pupil size were monitored by a miniature video camera inside the ganzfeld dome . if the subjects began to close their eyes during the exposure period , the experimenters reminded them to keep their eyes completely open . at 3 : 30 am , a second 10 ml blood sample was taken by venipuncture and the subjects were then permitted to leave the laboratory . eight wavelengths were studied for this action spectrum ( 440 , 460 , 480 , 505 , 530 , 555 , 575 and 600 nm ). across these wavelengths , each subject was exposed to complete darkness from 2 : 00 to 3 : 30 am on their control night and to a set of irradiances covering a 4 log unit photon density range of 10 10 to 10 14 photons / cm 2 on exposure nights . for the probe of sensitivity to monochromatic light at 420 nm , a group of 8 subjects were exposed to a single night of no light exposure and a single night of exposure to 420 nm light at 31 . 8 μw / cm 2 ( 5 . 58 × 10 13 photons / cm 2 ). as shown in fig5 , experimental light stimuli were produced by a 450 or 1200 w xenon arc lamp ( photon technology inc ., princeton , n . j .). each lamp was enclosed in a light proof chamber and cooled by water circulation . an exit beam of light from each source was directed by a parabolic reflector and , for the 1200 w lamps , excess heat in the light beam was reduced by a water filter . monochromatic wavelengths ( 10 - 14 . 5 nm half - peak bandwidths ) were produced by a grating monochromator and light irradiance was controlled by a manual diaphragm . the resulting light beam was directed into the top area of a ganzfeld apparatus and reflected evenly off the walls of the ganzfeld dome into volunteers &# 39 ; eyes . the entire reflecting surface of the dome was coated with a white material ( spectralite ) with a 95 - 99 % reflectance efficiency over the 400 to 760 nm range . routine measurement of the light irradiance ( μw / cm 2 ) was done with a tektronix j16 radiometer / photometer with a j6512 irradiance probe ( tektronix , beaverton , oreg .). experimental light stimuli reflected from the ganzfeld dome was measured at volunteers &# 39 ; eye level immediately before and after the 90 minute exposure . additional measures were taken each half hour of the exposure to insure stimulus stability and enable readjustment of the intensity if it varied . these spot measures were taken with a ft - 1 ° meter ( minolta , osaka , japan ). spectroradiometric assessment of the monochromatic wavelengths at the level of subjects &# 39 ; corneas was done with a portable spectroradiometer with a fiber optic sensor ( ocean optics s2000 ). this equipment was calibrated with a standard lamp traceable to the national institute of standards and technology ( nist ). in action spectroscopy , it is critical that the measured light stimuli are representative of the stimuli which actually reach the photoreceptors that mediate the photobiological response . in studies on light regulation of the circadian system , factors which can modify the measured stimulus before it reaches the photoreceptors include head and eye motion , squinting and eye closure , pupillary reflexes , and light transduction through the ocular media ( gaddy et al ., 1993 ; brainard et al ., 1997 ). most of these factors are controlled in the experimental technique described above . concerning light transmission through ocular media , the cornea and aqueous and vitreous humors normally transmit nearly 100 % of visible wavelengths to the retina and do not change substantively as the eyes age ( boettner and wolter , 1962 ). in contrast , the aging human lens develops pigmentation that attenuates the transmission of shorter visible wavelengths to the retina ( lerman , 1987 ; brainard et al ., 1997 ). in the present study , restricting the age of volunteers to 18 - 30 years controlled this factor . measurements of mean transmittance of 36 postmortem human lenses in this age range showed relatively even transmission from 440 to 600 nm . in contrast , there was a mean 45 % reduction in lens transmission at 420 nm compared to 460 nm ( brainard et al ., 1997 ). consequently , measured corneal light irradiances at 420 nm had to be adjusted to compensate for reduced stimulus transmission to the retina even in this relatively young study group . blood samples were collected in glass vacutainers which contained edta . plasma was separated by refrigerated centrifugation , aliquoted into cryogenic vials and stored at − 20 ° c . until assay . melatonin concentrations were assayed by radioimmunoassay using antiserum described by rollag and niswender , ( 1976 ). radiolabeled ligand was prepared by adding 10 μl of a dioxane solution containing 1 μmole 5 - methoxytryptamine and 1 μmole tri - n - butylamine to 250 μci ( 0 . 1 nmole ) dried bolton - hunter reagent ( new england nuclear corp ., boston , mass .). the reaction was allowed to proceed for one hour before adding 50 μl of aqueous sucrose ( 16 gm / ml electrophoresis buffer ) and purifying product by disc gel electrophoresis . duplicate aliquots of 200 μl of each unknown and control sample were extracted into 2 ml of chloroform . the chloroform was removed in a speedvac centrifuge ( savant instruments , holbrook , n . y .) and resuspended in 200 μl of assay buffer ( phosphate buffered saline , ph 7 . 4 , containing 0 . 1 % gelatin with 100 mg thimerosal / liter as a preservative ). the extracts were washed twice with 3 ml of petroleum ether , then evaporated to dryness in a speedvac before being resuspended in 200 μl of deionized water . approximately 50 , 000 cpm of radiolabeled ligand and a 1 : 256 , 000 dilution of antiserum ( r1055 , 9 / 16 / 74 ) was added to each unknown and a triplicate 2 - fold geometric series of standards ranging in concentration from 0 . 201 to 200 pg per 200 μl assay buffer . the final assay volume of buffer in each tube was 400 μl . at the end of the 48 hour incubation period , three ml of 95 % ethanol ( 4 ° c .) was added to each assay tube and the bound radioactivity precipitated by centrifugation at 2000 × g for 30 minutes . the supernatant was decanted and radioactivity in the precipitate was quantified . the quantity of melatonin immunoreactivity in the samples was calculated with the use of a computer program ( m . l . jaffe and associates , silver spring , md . ; see davis et al ., 1980 ). all solutions were maintained at 4 ° c . throughout the radioimmunoassay procedure . assay results were not corrected for recovery ( which has proven to be & gt ; 95 % in independent trials ). the minimum detection limit of the assay is 0 . 5 - 2 . 0 pg / ml . two - tailed , paired student &# 39 ; s t tests were used to assess statistical significance of raw melatonin change from 2 : 00 to 3 : 30 am . percent melatonin change scores were determined by the following formula : percent ⁢ ⁢ melatonin ⁢ ⁢ change ⁢ ⁢ score = 100 × 03 ⁢ : ⁢ 30 ⁢ ⁢ h ⁢ ⁢ melatonin - 02 ⁢ : ⁢ 00 ⁢ ⁢ h ⁢ ⁢ melatonin 02 ⁢ : ⁢ 00 ⁢ ⁢ h ⁢ ⁢ melatonin ⁢ percent melatonin change scores then were normalized to percent control - adjusted change scores by subtracting the control ( no light ) condition percent change scores for each subject from that same subject &# 39 ; s light exposure score . this technique accounts for the normal individual rise or fall in plasma melatonin levels with respect to the light - induced changes ( gaddy et al ., 1993 ; brainard et al ., 1997 ). for data from each wavelength , complete sets of pre - exposure melatonin values , percent melatonin change scores , and percent control - adjusted melatonin change scores were analyzed with one way , repeated - measures anova . significant differences between groups were assessed with post - hoc scheffe f - tests with alpha set at 0 . 05 . the group of single fluence - response curves ( one for each wavelength ) was fitted to a parametric model in which the melatonin response ( y ) to a photon dose ( x ) is predicted by : the theoretical initial y - response ( 0 dose ) for the curve ( a 1 ); the theoretical final y - response (“ infinite ” dose ) for the curve ( a 2 ); the dose producing a response halfway between a 1 and a 2 ( x 50 or ed 50 ); and the slope estimator ( p ) for the slope of the curve between a 1 and a 2 . the equation is : y = a 1 - a 2 1 + ( x / x 50 ) ⁢ p + a 2 the computer program origin 6 . 0 ( microcal , northampton , mass .) was used to fit the fluence - response curves to the data . from extensive experience in our laboratory , a saturating 90 minute light exposure produces a maximum mean percent control - adjusted plasma melatonin suppression ranging from 60 to 80 % depending on the particular group of subjects being tested ( gaddy et al ., 1993 ; ruberg et al ., 1996 ; wang et al ., 1999 ; brainard et al ., 2000 ; 2001 ). to form an analytical action spectrum , it is necessary to determine if all fluence - response curves can be fit to a univariant sigmoidal curve ( lipson , 1994 ; coohill , 1991 ; 1999 ). to do this , sigmoid curves were fitted to the five fluence - response curves between 440 nm and 530 nm which reached a mean percent control - adjusted melatonin suppression of 60 - 80 % by constraining the a 1 factor ( theoretical initial y - response ) to 0 since no light exposure should yield a 0 % control - adjusted plasma melatonin suppression . from this set of curves , a mean a 2 ( theoretical final y - response or “ infinite ” dose for the curve ), and a mean p ( slope estimator ) was calculated . subsequently , all 8 data sets ( including the data sets which did not reach saturation ) were then fitted to sigmoid curves that constrained a 2 and p to these means and constrained a 1 to 0 . each calculated curve was tested for goodness - of - fit of the data by coefficient of correlation . this action spectrum was formed from the photon density which elicited the half - saturation constant ( ed 50 ) of the percent control - adjusted melatonin suppression for each of the 8 wavelengths . these half - saturation constants were derived from the 8 univariant fluence - response curves described above . the half - saturation constants were then normalized to the maximum response and plotted as relative sensitivity . the relative quantum sensitivity from each group of subjects was then graphically plotted ( quanta / wavelength ) to illustrate the resultant action spectra for melatonin suppression in humans . a predicted peak sensitivity for this action spectrum was determined by fitting a vitamin a 1 - retinaldehyde photopigment template to the data by a modification of the method described by macnichol ( 1983 ). specifically , the long wavelength limb of vitamin a 1 - based photopigments can be considered linear within the 10 - 90 % sensitivity range when plotted on a frequency abscissa . to select the best fit vitamin a 1 template , the normalized 10 - 90 % long wavelength melatonin ed 50 data were fitted to a series of vitamin a 1 - based templates within the 10 - 90 % sensitivity range of the templates &# 39 ; long - wavelength limbs ( partridge and de grip , 1991 ). pearson correlation coefficients derived from fitting the melatonin data to the templates indicated the optimum fitting template . individuals vary slightly in their pupil size and response to mydriatic agents . mean ± sd pupillary dilation was 7 . 19 ± 0 . 88 mm for all 72 subjects across all nights of exposures . there were no significant pupil size changes during the light exposures . similarly , there is a small degree of variability in exact light exposure durations due to slight experimental delays . across 627 single - subject experiments , the mean ± sd exposure duration was 90 . 6 ± 2 . 1 minutes . a total of 53 assays were run to quantify melatonin in plasma samples collected during this project . coefficients of variation calculated from control samples assayed as 19 . 2 pg / ml and 90 . 0 pg / ml had 10 . 8 % and 4 . 0 % for intra - assay coefficients of variation , respectively . the inter - assay coefficients of variation were 13 . 5 % and 10 . 2 %. since the predicted peak of the final action spectrum is 464 nm , the full data complement , from raw melatonin values to a final fluence - response curve for the nearby monochromatic stimulus at 460 nm , is illustrated in fig2 - 4 . this fluence - response study at 460 nm was done with 8 subjects ( 4 males , 4 females ). across these subjects on all nights of testing , there were no significant differences ( f = 0 . 70 , p = 0 . 69 ) between sets of pre - exposure values indicating that baseline nocturnal melatonin levels were consistent across the different nights of study . fig6 shows the mean + sem pre - and post - exposure ( 2 : 00 to 3 : 30 am ) melatonin values ( mean range 72 . 1 − 29 . 3 pg / ml ). at 460 nm , exposure to irradiances of 2 . 3 μw / cm 2 and lower did not significantly suppress plasma melatonin . in contrast , exposures of 3 . 1 μw / cm 2 and higher elicited significant melatonin suppressions ( p & lt ; 0 . 03 or less ). for comparative purposes , all melatonin data were converted to plasma melatonin percent control - adjusted change scores . as illustrated in fig7 , one - way , repeated measures anova showed a significant effect of light intensity on plasma melatonin percent control - adjusted change scores ( f = 14 . 92 , p & lt ; 0 . 0001 ). post - hoc tests on plasma melatonin percent control - adjusted scores demonstrated that all intensities at or above 3 . 1 μw / cm 2 significantly suppressed melatonin more than 0 . 012 μw / cm 2 ( p & lt ; 0 . 05 or less ). similarly , all irradiances at or above 12 . 1 μw / cm 2 significantly suppressed melatonin more than 1 . 5 μw / cm 2 . finally , both 24 . 2 and 42 . 2 μw / cm 2 exposures elicited significantly higher plasma melatonin percent control - adjusted change scores compared to an irradiance of 2 . 3 μw / cm 2 . the data from fig7 can be mathematically converted into a best fit , sigmoidal curve which plots melatonin suppression against stimulus photon density . the specific formula for this curve is shown below and has a 0 . 97 coefficient of correlation ( r 2 ). y = 7 . 17 - 73 . 4 1 + ( x / 8 . 29 ) 1 . 23 + 73 . 4 as shown in fig8 , this curve illustrates the fluence - response interaction between mean ± sem melatonin percent control - adjusted change scores and the photon density of the monochromatic light . as shown in fig6 - 8 , there is a clear , fluence - response relationship between graded photon densities of monochromatic 460 nm light and melatonin suppression . data from each of the 8 wavelengths tested in this study fit four - parameter sigmoidal curves with high coefficients of correlation . specifically , wavelengths at 440 , 460 , 480 , 505 , 530 , 555 , 575 and 600 nm had respective coefficients of correlation ( r 2 ): 0 . 99 , 0 . 97 , 0 . 95 , 0 . 97 , 0 . 98 , 0 . 92 , 0 . 96 , and 0 . 97 . as described in the methods , to form an analytical action spectrum , all fluence - response curves must be fit to a univariant sigmoidal curve ( lipson , 1994 ; coohill , 1999 ). the univariant curve model for the data in this study has the factors of a 1 = 0 , a 2 = 66 . 9 , and p = 1 . 27 . fig5 illustrates all 8 univariant fluence - response curves from this study . as with previous circadian analytical action spectra ( takahashi et al ., 1984 ; provencio and foster , 1995 ; yoshimura and ebihara , 1996 ), full range fluence - response curves were not elicited above 550 nm . despite this , standard photobiological curve fitting methods could be used to fit the data from all eight wavelengths in the present study to univariant , sigmoidal functions . when fit to a univariant fluence - response curve with these factors , the data from exposures to 440 , 460 , 480 , 505 , 530 , 555 , 575 and 600 nm have high coefficients of correlation of 0 . 91 , 0 . 95 , 0 . 93 , 0 . 94 , 0 . 92 , 0 . 90 , 0 . 95 , and 0 . 81 , respectively . given the high sensitivity of subjects to short wavelength light as shown in fig9 , it was determined that a probe of sensitivity to monochromatic light below 440 nm was needed . on the control night when the eight volunteers were exposed to darkness only , their raw mean melatonin levels at 2 : 00 and 3 : 30 am were 69 . 4 and 76 . 0 pg / ml , respectively . that small increase was not statistically significant ( t =− 1 . 15 , p = 0 . 29 ). as shown in fig1 , when these volunteers were exposed to 420 nm light at 31 . 8 μw / cm 2 ( 5 . 58 × 10 13 photons / cm 2 ), raw mean melatonin levels at 2 : 00 and 3 : 30 am were 76 . 4 and 47 . 6 pg / ml , respectively . that decrease in melatonin was statistically significant ( t = 4 . 67 , p & lt ; 0 . 003 ). for comparative purposes , this single melatonin suppression response was fitted to the univariant fluence - response curve formula used for all of the data in fig9 . the resulting curve estimated a half - maximum ( x 50 or ed 50 ) melatonin suppression response for 420 nm of 1 . 83 × 10 13 photons / cm 2 . action spectra are determined by comparing the number of photons required for the same biological effect at different wavelengths ( smith , 1989 ; coohill , 1999 ). for this experiment , the action spectrum was formed from the photon density which elicited the half - saturation constant ( x 50 or ed 50 ) of the percent control - adjusted melatonin suppression for each of the eight wavelengths . the half - saturation constants were derived from the eight univariant fluence - response curves shown in fig9 and the one estimated half - saturation constant from the data shown in fig1 . the relative quantum sensitivity from each group of subjects was plotted in fig1 ( quanta / wavelength ) to illustrate the resultant action spectra for human melatonin suppression . when the data were aligned to the best - fit template for vitamin a 1 - retinaldehyde photopigments , this action spectrum predicted a peak spectral sensitivity ( 1 max ) of 464 nm . there was a strong coefficient of correlation between the data and this fitted opsin nomogram ( r 2 = 0 . 91 ). the action spectrum for the photoreceptor system which provides input to the pineal gland appears to be distinct from the action spectra for the classical human visual photoreceptor systems . to illustrate this , the maximal spectral absorbencies and long wavelength limbs of the human rod and cone photoreceptors that support vision ( stockman and sharpe , 1999 ) are illustrated in fig8 along with the maximal spectral absorbence and long wavelength limb of the melatonin action spectrum . the shaded area around the melatonin action spectrum illustrates ± sd for this function . the action spectrum presented here is based on univariant fluence - response curves for melatonin suppression by eight monochromatic light wavelengths in healthy subjects . these data fit a vitamin a 1 opsin template with 446 - 477 nm providing the strongest circadian input for melatonin regulation . these results suggest a novel photopigment in the human eye may be primarily responsible for melatonin regulation and may be distinct from the individual rod and cone photoreceptors for vision . in developing a fluence - response curve , a complete within - subjects experimental design produces the most reliable results . when subjects are studied over a two to four month period , however , lack of stability in the subjects &# 39 ; circadian entrainment can introduce variability in light - induced melatonin suppression . this study accepted only volunteers who reported regular bed and wake times and their melatonin rhythms appeared to have been stable during the course of the study . as shown in the 2 : 00 am melatonin values ( fig6 ), there were no significant differences between sets of pre - exposure values indicating that baseline melatonin levels were consistent across the different study nights . this phenomenon has been documented for the 505 nm fluence - response group as well as in other similarly controlled studies ( brainard et al ., 1997 ; 2000 ; 2001 ; wang et al ., 1998 ). this within - subject stability of the melatonin rhythm over time has been frequently confirmed in the literature ( waldhauser and dietzel , 1985 ; arendt , 1988 ; 1998 ). the data from each wavelength studied fit a univariant four parameter sigmoidal curve with a high coefficient of correlation . the univariance of these curves is consistent with , but does not prove , the hypothesis that melatonin suppression is modulated by a single photoreceptor type . previous studies with animals and humans have illustrated similar fluence - response relationships for melatonin suppression and other circadian responses with monochromatic and broad spectrum light ( brainard et al ., 1983 ; 1988 ; podolin et al ., 1987 ; mcintyre et al ., 1989 ; nelson and takahashi , 1991 ; zeitzer et al ., 2000 ; dkhissi - benyahya et al ., 2000 ). the initial attempts to define circadian and neuroendocrine responses to photons of different wavelength began with polychromatic action spectra which tested single irradiances of broader light bandwidths in various rodent species . these polychromatic action spectra were reasonably consistent in indicating that the spectral region between 450 - 550 nm provides the strongest stimulation of circadian and neuroendocrine responses in rodents ( for review : brainard et al ., 1999 ). analytic action spectra , based on sets of fluence - response curves at different monochromatic wavelengths , are superior for identifying photoreceptors that mediate photobiological responses ( lipson , 1994 ; coohill , 1999 ). there are four analytic action spectra on circadian and neuroendocrine regulation in hamsters , rats and mice ( takahashi et al ., 1984 ; bronstein et al ., 1987 ; provencio and foster , 1995 ; yoshimura and ebihara , 1996 ). data from these action spectra have been fitted to spectral sensitivity curves for retinal - based visual photopigments . this curve fitting is predicated on the assumption that a retinal - based molecule transduces light stimuli for circadian regulation , and allows the prediction of the shape of the photopigment absorption spectrum as well as its peak sensitivity ( 1 max ). across these studies which employed different circadian endpoints , the predicted 1 max ranges from 480 - 511 nm and is surrounded by a broad region of high sensitivity . from these results , different photopigments have been suggested to be responsible for circadian regulation , including rhodopsin , a rhodopsin - like molecule , a middle wavelength cone photopigment , or an ultraviolet cone photopigment . it is commonly believed that the photopic visual system has a peak wavelength sensitivity around 555 nm ( rodieck , 1998 ). many investigators have hypothesized that the photopic visual system mediates circadian and neuroendocrine responses , since this part of the visual system is responsive to “ bright ” daytime levels of illumination . previous data ( brainard et al ., 2001 ) and those presented above do not support this view . the results clearly demonstrate that 555 nm is significantly weaker in suppressing melatonin compared to an equal photon density of 460 nm . thus , the photopic system is not likely to be the primary input for circadian regulation . demonstrating that the photopic visual system is not the principal phototransducer for melatonin regulation does not preclude it from having any role in circadian input . indeed , recent studies suggest that visual cones may be involved in circadian regulation . recordings from scn neurons in rats indicate that the visual rods and cones provide input to cells of the rat scn ( aggelopoulos and meissl , 2000 ). similarly , a human phase - shifting study suggests that , under some circumstances , the visual long wavelength - sensitive cone may also mediate circadian vision in humans ( zeitzer et al ., 1997 ). the data presented here do not support the view that any of the known visual photoreceptors provide the primary input for melatonin regulation . fig1 shows that none of the action spectra for individual visual photoreceptor systems match the action spectrum for melatonin suppression . if the photoreceptors that mediate vision in humans are not the primary photoreceptors for circadian regulation , what are the alternative candidates ? recent studies with various vertebrate species have identified several new molecules which may serve as circadian photopigments . these putative photopigments include both opsin - based molecules such as vertebrate ancient ( va ) opsin ( soni and foster , 1997 ), melanopsin ( provencio et al ., 1998 ), and peropsin ( sun et al ., 1997 ), as well as non - opsin molecules like biliverdin ( oren , 1996 ) and cryptochrome ( miyamoto and sancar , 1998 ). among these new photopigments , only melanopsin has been specifically localized to the human neural retina ( provencio et al ., 2000 ) and cryptochrome has been localized to the mouse neural retina ( miyamoto and sancar , 1998 ). cryptochromes have been studied extensively as circadian photoreceptors in plants and insects ( ahmad and cashmore , 1993 ; stanewsky et al ., 1998 ), and have been proposed as circadian photoreceptors in mammals ( miyamoto and sancar , 1998 ; thresher et al ., 1998 ). the contention that cryptochromes serve as circadian photoreceptors in humans or other mammals , however , remains controversial ( van der horst et al ., 1999 ; griffin et al ., 1999 ; von schantz et al ., 2000 ). the action spectrum presented here matches a vitamin a 1 - retinaldehyde photopigment template which supports the hypothesis that one of the new opsin photopigment candidates provides primary photic input for melatonin regulation in humans . the molecular identification of candidate opsin or non - opsin photoreceptors and their localization in the retina and / or neural components of the circadian system make them well - suited to act as circadian phototransducers . are the effects of light on melatonin suppression relevant to general circadian regulation ? studies have shown that hamsters have a higher intensity threshold for light - induced phase - shifts of wheel running rhythms than for melatonin suppression ( nelson and takahashi , 1991 ). recently , however , a study on humans showed that the 50 % response sensitivity for circadian phase - shifting ( 119 lux ) was only slightly higher than that for melatonin suppression ( 106 lux ) with white light ( zeitzer et al ., 2000 ). it is possible that there are separate photoreceptors for mediating circadian entrainment versus acute suppression of melatonin . it is reasonable , however , to conclude that a variety of non - 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