The traditional light source for contact printing has always been a plain, ordinary light bulb of sufficient intensity. That was all that was needed in the days when we had silver chloride contact printing paper such as Azo. No collimation or diffusion necessary.

Now that those papers are gone and we are printing on enlarging paper, the light intensity has to be much, much lower, hence, more widespread use of enlargers as the light source. I recently measured the light intensities I frequently use just for trivia's sake. For Azo printing, I used a 120 watt bulb, four feet above the frame. Intensity was 70 foot-candles. Under the enlarger using enlarging paper, a typical intensity is 0.43 foot-candles. That's three orders of magnitude less intensity.

But, other than the inherent tonal characterisitcs of the respective papers, my negatives haven't cried one tear about being printed with a bare light bulb or the collimated condenser enlarger source.