A system for spectral reading includes a plurality of LEDs, an interface, and a processor. The plurality of LEDs are disposed in a physical array. Light from the plurality of LEDs is enabled to be collimated at a Fabry-Perot etalon. The interface is configured to receive a gap calibration table and power characteristics of a plurality of LEDs. The processor is configured to determine an LED switch table. The LED switch table indicates a set of the plurality of LEDs with power above a threshold at a plurality of wavelengths. The processor is further configured to cause measurement of a sample using the gap calibration table and the LED switch table for a set of gap values and determine measurement results.