Improved safety for viewing gas spectra in your classroom. The Hydrogen Safe Spectrum Tube offers extended life because it has a hard polymer shell to protect against breakage and no internal electrodes. Tube is 15.5 x 4.0 x 3.0 cm. Requires Safe Spectrum System Single-Tube Power Supply (item #755500) or Safe Spectrum System 8-Tube Carousel Power Supply (item #755502). Up to 40 hr burn time.