A device, comprising: at least a first group of solid state light emitters that emit light having a first dominant wavelength and a second group of solid state light emitters that emit light having a second dominant wavelength in the range of from 600 nm to 630 nm; at least a first sensor positioned to be exposed to at least a portion of light emitted by said first and second groups of solid state light emitters, the first sensor configured to be sensitive to light emitted by at least said first group of solid state light emitters, the first sensor a photodiode, the first sensor configured to not be sensitive to light emitted by said second group of solid state light emitters; and circuitry configured to adjust a current and/or voltage of electrical signal supplied to said second group of solid state light emitters, based only on: a signal representing an intensity of light detected by the first sensor, said circuitry comprising a differential amplifier sub-circuit, the differential amplifier sub-circuit comprising at least a first comparator, and a difference, detected by a second comparator, between a first voltage at an output from the first comparator and a second voltage based on electrical current supplied to the second group of solid state light emitters and modified by a voltage divider circuit consisting of a first resistor R a, a second resistor R b and a thermistor R T, connected such that the first resistor is in series with the second group of solid state light emitters, and a node between the first resistor and the second comparator is connected to ground through the thermistor and the second resistor in series, a first input of the first comparator and a second input of the first comparator electrically connected relative to the first sensor such that the first and second inputs of the first comparator will pick up the same or roughly the same interference, which will cancel out at the first comparator. at least a first group of solid state light emitters that emit light having a first dominant wavelength and a second group of solid state light emitters that emit light having a second dominant wavelength in the range of from 600 nm to 630 nm; at least a first sensor positioned to be exposed to at least a portion of light emitted by said first and second groups of solid state light emitters, the first sensor configured to be sensitive to light emitted by at least said first group of solid state light emitters, the first sensor a photodiode, the first sensor configured to not be sensitive to light emitted by said second group of solid state light emitters; and circuitry configured to adjust a current and/or voltage of electrical signal supplied to said second group of solid state light emitters, based only on: a signal representing an intensity of light detected by the first sensor, said circuitry comprising a differential amplifier sub-circuit, the differential amplifier sub-circuit comprising at least a first comparator, and a difference, detected by a second comparator, between a first voltage at an output from the first comparator and a second voltage based on electrical current supplied to the second group of solid state light emitters and modified by a voltage divider circuit consisting of a first resistor R a, a second resistor R b and a thermistor R T, connected such that the first resistor is in series with the second group of solid state light emitters, and a node between the first resistor and the second comparator is connected to ground through the thermistor and the second resistor in series, a signal representing an intensity of light detected by the first sensor, said circuitry comprising a differential amplifier sub-circuit, the differential amplifier sub-circuit comprising at least a first comparator, and a difference, detected by a second comparator, between a first voltage at an output from the first comparator and a second voltage based on electrical current supplied to the second group of solid state light emitters and modified by a voltage divider circuit consisting of a first resistor R a, a second resistor R b and a thermistor R T, connected such that the first resistor is in series with the second group of solid state light emitters, and a node between the first resistor and the second comparator is connected to ground through the thermistor and the second resistor in series, a first input of the first comparator and a second input of the first comparator electrically connected relative to the first sensor such that the first and second inputs of the first comparator will pick up the same or roughly the same interference, which will cancel out at the first comparator.