Here is a posting of the machine I assembled, the last posting illustrates that the light source quality (the LED) is an important contributor to the quality of the scan.
The simple answer:
- An incandescent bulb light is driven by the voltage (V) across the lamp. The bulb is acts as a resistor, and it has no polarity. It would work with alternating or direct voltate (AC or DC). Although for scanning it may be best to use DC.
- The LED light is driven by the current (I), the LED is a diode and will illuminate when the current has the appropriate polarity. It also has a minimum voltage to make the diode work (Vf in the specifications). What the drivers typically do is to regulate the current, which can also be achieved by a resistor.
As part of the quality there are a couple of aspects to consider: the spectrum of the light source (AKA the CRI), and also as important, how even the light is across the film surface. Here is an article (in spanish) on the subject of making the light source even.
As previous comments suggest, intensity and color control have significant complexity and are not necessary required to start.
Hope it helps.
PS. by intensity I mean the ability to dim manually or controlled; by color the ability to mix color LEDs for color correction.