I have need of a spectrometer to assist me in my artwork, so I plan to build one. Some of the paints I use are opaque, and many are transparent. I want to capture the spectrum as they would look painted over white canvas, or painted over other colors in several layers, so I will be reflecting light from the sample into the spectrometer, not looking directly at the sample through a light source. I have a Raspberry Pi with a touchscreen, the camera for the Pi, and a diffraction grating at 1,000 lines per inch. There are instructions for construction of the spectrometer on the web, so I'm not asking about that. It's the illumination that concerns me. Ideally natural daylight is the best source, but artificial lighting may be necessary. Can I just put white LEDs onto a white paper, and normalize the intensity to mimic daylight in software? Then when I illuminate the sample, it's just a multiplication for the return light at that frequency to get what would be the reflectance in daylight. Can I get a better approximation of daylight by mixing white LEDs with halogen bulbs, or would that be unnecessary since I have to normalize the source anyway? It's the illumination aspect of the project that I wonder about. Is the project even possible using reflected light? Will it be bright enough after passing through a slit? I'm going to experiment and build it anyway, but the advice of anyone with experience would be much appreciated.