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The absence of particular spectral lines of a given element could only mean that the conditions (such as temperature) aren't right to make the transition associated with that line very probable. This is because some lines require a limited temperature range to first get the atoms to an excited state, from which they then make the transition in question. For example, the hydrogen Balmer series lines cannot be seen (even if hydrogen is present) unless the temperature is not too hot, and not too cold. They are strongest for T near 10,000 K.