----------------------LED----------------------

                      Bit size = 7 micro inches = 0.18 micro meters 
"common cathode"      7-seg displays. 
                           ------                   -----
                      +5V 5|    |2,3,6,7,10 - Gnd  8|    |13 -270ohm-|>-|
                      sw 14|7490|1,12 ------------ 7|7448|12 -270ohm-|>-|
                           |    |9 --------------- 1|    |11 -270ohm-|>-|
                           |    |8 --------------- 2|    |10 -270ohm-|>-|
                           |    |11 -----*-------- 6|    |9 --270ohm-|>-|
                            ----              +5V 16|    |15 -270ohm-|>-|
                                                    |    |14 -270ohm-|>-|
                                                     ----          Gnd  +
                      **[Just a note from me, 
                      need a DE-BOUNCED switch circuit or the
                      counter be counting the bounces of switch!! 
                      "switch point" sw is connected to +5V 
                      the counter will count by one. 
                      If you want to add a second digit, 
                      take a wire off the point marked * 
                      and connect this into  sw point 
                      of an identical circuit. 
                      Those on the right are the bits of
                      the LED display, by the way. 
                      You need to connect the "8" with its pins as follows:
                           13
                         ------
                      15 |    | 12  
                      14 ------
                       9 |    | 11
                         ------
                           10
                      can use 74LS90/74LS48 or even 74HC90/74HC48s,

----------------------------------------------------------------------------

Red LEDs              11-22+ lumens/watt by Agilent,
                      Red-Orange LEDs   - 21-22 maybe now 28.5 lumens/watt by 
                      Yellow-Green LEDs - 3-4 lumens/watt 
                      Green LEDs - 25-32+ sometimes 42 lumens/watt by Nichia, 
                      Blue LEDs - 7.5-probably 8, rarely 10 lumens/watt by 
                      Voltage drop at 20 mA was mostly 3.45-3.5 volts. Estimated 
luminous efficacy     of  emitted light was mainly 450-475 lumens per watt, 
                      maybe as low as 420-440 for bluest one 
                      and as high as 520-525 for one that was
                      noticeably more of a lime green than the other 55 of the 
                      56 good pieces.
----------------------------------------------------------------------------
lumen                 unit of light output, equal to 1 / (60 * pi) 
                      light emitted by one square centimeter 
                      ideal blackbody surface at melting point of platinum.
                      IF spectrum differs from blackbody at melting point of platinum, 
                      equate lumens by applying  official photopic function to the
                      quantity of light at every wavelength present.
----------------------------------------------------------------------------

LED                   deposit three semiconductor layers on a substrate. Between
                      an active region Between p-type and n-type semiconductor layers  
                      emits light when an electron and hole  recombine.
when forward biased   holes from p-type and electrons from n-type driven into active region. 
light is produced     by a solid state process called electroluminescence.
                      layers of the LED emit light all the way around layered structure, and
                      LED structure is placed in a tiny reflective cup
                      so  light from active layer reflected desired 

                                      #####____
                                     #   / #  /|
                                    #   /____/ |
                                    #   |    | |
                                    #   |    | |
                                    #   |    | |
                                     #  |    | |
                                   __#__|____|_|_
                                 /   #           /|
                                /    #          / |
                               /       +1.9V   / /|=> Light Out
                              /               / / |
                             /_______________/ / /|
                             |P_TYPE         |/ / |
                             |_______________| / /|__
                             |ACTIVE_REGION  |/ / / /|
                             |_______________| / / / |
                             |N-TYPE         |/ / / /
                             |_______________| / / /
                             |SUBSTRATE      |/ / /
                            _|_______________|_/ /
                           |        GND        |/
                           |_______    ________|
                                   |   |
                                   |   |
                                   |   |
                      

Wavelength of LED     or Laser based on band-gap voltage
                      voltage drop is close to the band gap of a forward biased diode.
                      l = 1240 / E
                      l = wave length in nm
                      E = band-gap voltage
                      red LEDs with a 1.9V drop run about 652 nm. (GaAs0.6P0.4)
Calc_WaveLength       =====Cut_Paste_Into_Formula_Calculator===================
                      LED_WaveLength_nm=1240/E_bandgap_V
                      E_bandgap_V=1.9=BandGapVoltage_LED
----------------------------------------------------------------------------

Blue LED Lamps!       in urban areas at night, blue lights have a tendency to
                      stand out.  for police emergency phones 
                      of blue lights was a result of "blue impact"  or 
                      stimulation of blue-sensing light sensors in human eyes.
                      Back when lumen was defined in terms of 
                      photopic function (1931 CIE "Y-bar" function), blumens 
                      equals lumens times ratio z to y chromaticity coordinates
                      1988 redefinition of photopic function messes this up, 
                      LED blue lights for police emergency phones. Most have 
                      usual 470  nm blue LEDs.
                      current bright blue LEDs around 466-470 nm. 
                      blue peak of human vision is a little
                      below 450 nm.