How to make LED bar graphs to measure intensity
LM3914 / LM3915 / LM3916  will do this job directly. There are other ICs that will do similarly. Search for "bar graph driver". 



These will interface more or less directly in place of the 2N3904 transistors in your circuit. (Just as the SSR's would that I provided references to yesterday). Some minor component changes may be needed. 


LM3914 - linear
LM3915 - log response
LM3916 - "extended logarithmic" VU meter type display.


NatSemi product page

Also lists I^2C only (not analog input) LP3944, low voltage, 8 LEDs. LP3943, low voltage , 16 LEDs. 

Datasheets:


LM3914
LM3915
LM3916


IIC only - LP3943 product page

Pricing - Digikey, in stock


LM3914 pricing
LM3915 pricing
LM3916 pricing


Note below - display can be a bar or individual dot at selected level. 

Edited relevant parts from LM3914 overview. Others similar


Drives LEDs, LCDs or vacuum fluorescents
Bar or dot display mode externally selectable by user
Expandable to displays of 100 steps
Internal voltage reference from 1.2V to 12V
Operates with single supply of less than 3V
Inputs operate down to ground
Output current programmable from 2 mA to 30 mA
Input withstands ±35V without damage or false outputs
LED driver outputs are current regulated, open-collectors
Outputs can interface with TTL or CMOS logic
The internal 10-step divider is floating and can be
referenced to a wide range of voltage