1. The problem statement, all variables and given/known data A lifetime of the first excited state for some atom is τ, calculate natural line width for that line. 3. The attempt at a solution Well, I could use energy-time uncertainty relation ΔE*Δt=h then ΔE*τ=h , now I can use a relation E=hc/λ to obitain Δλ=c*τ , which is natural line width. Now let's say τ=17ms (something like the lifetime of the Fe xiv) then Δλ=3*10^8*17*10^-3=50*10^5m , this can not be true, what am I doing wrong ?