This picture shows all three tubes in operation looking at them with the naked eye. Notice that the upper 25 mm Argon tube is about as bright as the 25 mm diameter electrode end of the lower 10 mm diameter restricted bore Argon tube. Note that the center of the 10 mm Argon tube is much brighter than the discharge in the upper 25 mm Argon tube. This is due to the higher power density in the smaller tube. The power to each of the Argon tubes is about 18 watts. The power to the center (Hydrogen) tube is about 180 watts. Note that the Hydrogen tube radiates more strongly in the blue end of the spectrum. The power density in the lower Argon tube is almost ten times the power density in the upper Argon tube.