Following the definition of incandescence, what are two practical effects of heating materials hotter (analysis focused)?

Lets say you want to measure the absorbance of a colored dye by building your own instrument. You know it absorbs visible light, so you want to use a tungsten bulb as the light source. Tungsten bulbs output continuously in the entire visible range, so you know this source will produce wavelengths the molecule will absorb. Why is a wavelength selector even needed?

Despite the much lower cost, many spectroscopists opt to spend the $15,000 on the catalog of interference filters. Describe TWO reasons why they would do this?