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Woody,
The 1 hour progressive turn-on time for your LED driver seems to make inexpensive analog solutions impractical. So, a 5V microP with a DAC output, driving a GND referenced opamp, driving a NPN or N mosfet current source would seem to be simple and cheap.
A LM324 class opamp (cheap, rugged) has common-mode range down to GND so its reference input could be directly driven from the DAC out. The sense resistor on the Em (Source) to GND would be scaled for 500mA at max DAC output voltage. The LM324 could be powered from your LED bulk supply. The programming could be changed to accomodate various turn-on/off strategies, and unused inputs could be programmed for external sensors for additional contol options.
You could use a large variety of cheap PIC processors, or Basic programmed derivatives, should you wish to avoid the obtuse and frustrating initialization for the bare PIC's. My favorite derivative is the PICAXE from the UK (Revolution?). A suitable microP would cost less than $10. One reseller in the USA is phanderson.com. He is a prof. at Towson State in MD and has written a lot of microP applications material on the web in support of his classes using microP's. If you DIY for the programming support hardware; you can get away for less than $10 (assuming you have a PC available). Manuals/Forum/PC Software free on the web from the UK.
Just a thought!
VSR
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Need a soft start current source
