A handheld aerosol-generating device may include an emitter configured to emit light, a sensor configured to receive light, and an aerosol chamber configured to hold an aerosol. The emitter may emit light into the aerosol chamber. The sensor may receive light from the aerosol chamber and measure at least one wavelength of the spectrum of the received light. Direct measurement of parameters, and/or the presence, of the aerosol in the aerosol chamber may be enabled, where the direct measurement of parameters of the aerosol in the aerosol chamber may enable optimal operation of an aerosol-generating system that may be the handheld aerosol-generating device.