C.I.E. Photopic Luminous Efficiency Function:
--------------------------------------------

The 1931 Y function is a linear combination of red, green, and blue cone
responses, with negligible weight to blue and heavier weight to green and
red.  The X function is a linear combination of all three, with more red
than blue, and the green's coefficient being negative.  The Z function is
close to just the blue cone response.

Chromaticity coordinates (lower case x, y, and z) for a given wavelength
are X, Y, and Z divided by the sum of all three.  For non-monochromatic
light, add up the X, Y, and Z for each wavelength, then divide these three
totals by the sum of all three.

In 1988 CIE updated the Photopic Luminous Efficiency Function because the
1931 function did not sufficiently weight the higher blue response of
young people.

   ******** 1988 C.I.E. Photopic Luminous Efficiency Function ********

  Wavelength    +0 nm       +1 nm       +2 nm       +3 nm       +4 nm
----------------------------------------------------------------------------
    380 nm    0.0002000   0.0002280   0.0002610   0.0002990   0.0003440
    385 nm    0.0003960   0.0004550   0.0005250   0.0006040   0.0006960
    390 nm    0.0008000   0.0009160   0.0010500   0.0012000   0.0013600
    395 nm    0.0015500   0.0017500   0.0018800   0.0022300   0.0025000
    400 nm    0.0028000   0.0031200   0.0034600   0.0038300   0.0042300
    405 nm    0.0046600   0.0051200   0.0056200   0.0061700   0.0067600
    410 nm    0.0074000   0.0081500   0.0089600   0.0098300   0.0108000
    415 nm    0.0118000   0.0128000   0.0140000   0.0151000   0.0163000
    420 nm    0.0175000   0.0186000   0.0196000   0.0207000   0.0217000
    425 nm    0.0227000   0.0236000   0.0246000   0.0255000   0.0264000
    430 nm    0.0273000   0.0283000   0.0294000   0.0304000   0.0315000
    435 nm    0.0326000   0.0337000   0.0347000   0.0358000   0.0369000
    440 nm    0.0379000   0.0388000   0.0398000   0.0406000   0.0415000
    445 nm    0.0424000   0.0433000   0.0441000   0.0450000   0.0459000
    450 nm    0.0468000   0.0477000   0.0487000   0.0498000   0.0509000
    455 nm    0.0521000   0.0534000   0.0549000   0.0564000   0.0581000
    460 nm    0.0600000   0.0626000   0.0653000   0.0680000   0.0709000
    465 nm    0.0739000   0.0770000   0.0803000   0.0837000   0.0872000
    470 nm    0.0910000   0.0949000   0.0990000   0.1040000   0.1080000
    475 nm    0.1130000   0.1180000   0.1230000   0.1280000   0.1330000
    480 nm    0.1390000   0.1450000   0.1500000   0.1560000   0.1630000
    485 nm    0.1690000   0.1760000   0.1840000   0.1910000   0.1990000
    490 nm    0.2080000   0.2170000   0.2270000   0.2370000   0.2470000
    495 nm    0.2590000   0.2700000   0.2822900   0.2950500   0.3085700
    500 nm    0.3230000   0.3384000   0.3546800   0.3716900   0.3892800
    505 nm    0.4073000   0.4256200   0.4443000   0.4633900   0.4829300
    510 nm    0.5030000   0.5235600   0.5445100   0.5656900   0.5869600
    515 nm    0.6082000   0.6293400   0.6503000   0.6708700   0.6908400
    520 nm    0.7100000   0.7281800   0.7454600   0.7619600   0.7778300
    525 nm    0.7932000   0.8081100   0.8224900   0.8363000   0.8494900
    530 nm    0.8620000   0.8738100   0.8849600   0.8954900   0.9054400
    535 nm    0.9148500   0.9237300   0.9320900   0.9399200   0.9472200
    540 nm    0.9540000   0.9602500   0.9660000   0.9712600   0.9760200
    545 nm    0.9803000   0.9840900   0.9874800   0.9903100   0.9928100
    550 nm    0.9949500   0.9967100   0.9980900   0.9991100   0.9997400
    555 nm    1.0000000   0.9998500   0.9993000   0.9983200   0.9968900
    560 nm    0.9950000   0.9926000   0.9897400   0.9864400   0.9827200
    565 nm    0.9786000   0.9740800   0.9691700   0.9638500   0.9581300
    570 nm    0.9520000   0.9454500   0.9384900   0.9311600   0.9234500
    575 nm    0.9154000   0.9070000   0.8982700   0.8892000   0.8797800
    580 nm    0.8700000   0.8598600   0.8493900   0.8386200   0.8275800
    585 nm    0.8163000   0.8047900   0.7930800   0.7811900   0.7691500
    590 nm    0.7570000   0.7447500   0.7324200   0.7200000   0.7074900
    595 nm    0.6949000   0.6822100   0.6694700   0.6567400   0.6438400
    600 nm    0.6310000   0.6181500   0.6053100   0.5924700   0.5796300
    605 nm    0.5668000   0.5539600   0.5411300   0.5283500   0.5156300
    610 nm    0.5030000   0.4904600   0.4780300   0.4656700   0.4534000
    615 nm    0.4412000   0.4290800   0.4170300   0.4050300   0.3930300
    620 nm    0.3810000   0.3689100   0.3568200   0.3447700   0.3328100
    625 nm    0.3200000   0.3093300   0.2978500   0.2865900   0.2756200
    630 nm    0.2650000   0.2547600   0.2448800   0.2353300   0.2260500
    635 nm    0.2170000   0.2081600   0.1995400   0.1911500   0.1829700
    640 nm    0.1750000   0.1672200   0.1596400   0.1522700   0.1451200
    645 nm    0.1382000   0.1315000   0.1250200   0.1187700   0.1127600
    650 nm    0.1070000   0.1014700   0.0962000   0.0911000   0.0863000
    655 nm    0.0816000   0.0771000   0.0728000   0.0687000   0.0648000
    660 nm    0.0610000   0.0574000   0.0540000   0.0507000   0.0475000
    665 nm    0.0446000   0.0418000   0.0391000   0.0366000   0.0342000
    670 nm    0.0320000   0.0300000   0.0281000   0.0263000   0.0247000
    675 nm    0.0232000   0.0218000   0.0205000   0.0193000   0.0181000
    680 nm    0.0170000   0.0159000   0.0148000   0.0138000   0.0128000
    685 nm    0.0119000   0.0111000   0.0103000   0.0095300   0.0088500
    690 nm    0.0082100   0.0076200   0.0070900   0.0065900   0.0061400
    695 nm    0.0057200   0.0053400   0.0050000   0.0046800   0.0043800
    700 nm    0.0041000   0.0038400   0.0035900   0.0033500   0.0031300
    705 nm    0.0029300   0.0027400   0.0025600   0.0023900   0.0022400
    710 nm    0.0020900   0.0019500   0.0018200   0.0017000   0.0015900
    715 nm    0.0014800   0.0013800   0.0012900   0.0012000   0.0011200
    720 nm    0.0010500   0.0009770   0.0009110   0.0008500   0.0007930
    725 nm    0.0007400   0.0006900   0.0006430   0.0005990   0.0005580
    730 nm    0.0005200   0.0004840   0.0004500   0.0004180   0.0003890
    735 nm    0.0003610   0.0003350   0.0003110   0.0002890   0.0002680
    740 nm    0.0002490   0.0002310   0.0002150   0.0001990   0.0001850
    745 nm    0.0001720   0.0001510   0.0001490   0.0001380   0.0001290
    750 nm    0.0001200   0.0001120   0.0001040   0.0000973   0.0000908
    755 nm    0.0000848   0.0000791   0.0000739   0.0000689   0.0000643
    760 nm    0.0000600   0.0000560   0.0000522   0.0000487   0.0000454
    765 nm    0.0000424   0.0000396   0.0000369   0.0000345   0.0000321
    770 nm    0.0000300   0.0000280   0.0000261   0.0000244   0.0000227
    775 nm    0.0000212   0.0000198   0.0000185   0.0000172   0.0000161
    780 nm    0.0000150

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