Mobile solar power units are recognized as promising means of decreasing the dependence of the military on fossil fuel generated power. To date, a multitude of mobile solar powered systems are under development that range from human portable, highly flexible, photovoltaic blankets, solar powered aircraft, trailer based hybrid power units, and underwater sensor applications. Spectral radiometers are widely used to measure the spectrum of emitted, transmitted or reflected light of a given material in numerous fields of the modern economy. Applications of spectral radiometers include environmental monitoring (Sun, water, soil, flora, etc), production control (liquids, solids, solutions, etc), medicine (tissue, blood, drugs, solutions, etc), opto-electronics (light emitters), trade (food, and other perishable goods) as well as monitoring in the fields of military and security operations (such as, object identification and sensing). Current spectral radiometers generally require either sophisticated optical components for beam forming and diffraction, refined electronic components for the signal readout or moving parts which often lead to high production costs. Furthermore, conventional spectral radiometry systems are shock-sensitive; they require long measurement times, and they consume considerable amounts of electrical power, making their use in remote environments disadvantageous. In contrast, the instant invention discloses a spectral radiometer having a novel minimum size, having ultra-low power, having integrated data storage functionality and a battery lifetime of up to several years, including a range of from less than about 2 years or less up to at least about 5 years or more, such that 10 or 15 years or more can be achieved. In addition, the system can be produced at the expense of less than twenty dollars ($20) and features very high sensitivity and linearity. Because of the modularity of the system, adjustment to different wavelength-bands, as well as operational capabilities involving different light intensities are easily possible, providing a tailored solution to the customers' needs. There are no alternative devices having comparably small dimensions.