T-25 and T100 tubes use radioactive gas to generate luminosity. No batteries required. Steady glow with a half life of about 12 years, so they will eventually dim and burn out. I've seen T-25, not very bright. T-100 is much brighter but I haven't seen it in person. The other primary illumination source is Superluminova. It comes in colors with C-3 being the brightest. However, C-3 appears slightly green under normal lighting. C-1 is whiter in daylight but doesn't glow as brightly. All Superluminova requires a "charge" from a bright light to glow. I have a watch with T-25 tubes. Turn out the lights and I can't see the glow until my eyes adjust to the dark. I also have several watches with Superluminova. Very bright at first but they dim markedly within 15 minutes. As will the Lum-Tec. After about 8 hours, a watch with a generous application of good quality Superluminova will glow about the same as a T-25 tube, based on my experience. After that, the tube will be brighter. Brightest watch I ever had was a pilot watch by Debaufre. Had C-3 Superluminova. Excellent watch, too. Brightest watch I've ever seen is Panerai. Also, Superluminova but amazing glow. I can post pics if you're interested but it's all relative.