He-Ne lasers allow you to demonstrate refraction, reflection, light scattering, critical angle, convergence and divergence, polarization of light, and Brewster's angle. Modulated lasers allow you to demonstrate voice communication and to measure the speed of light. Hard-sealed with solid state electronics, narrow and stable wavelength stability and long coherence length. Includes operator manual. Choose 0.5mW or 0.8mW for standard lasers. Choose 0.8mW or 1.5mW for modulated lasers. Two year warranty. Each.