answer
a few things about candelas: It's a unit that measures the amount of *visible* light going in a certain direction per certain time, so it doesn't matter how long the lamp is operating or if it emits light in all directions or not. Second of all, to get the amount of candelas you need to take the spectral power distribution function of the lamp (which says how much power is being radiated for a particular wavelength of light), multiply it with something called "luminosity function", which is a weight function that gives the sensitivity of the human eye to a particular wavelength, and then sum over all the wavelengths. (BTW, this is all from wikipedia) I don't know how to compute these integrals, (because I don't know how those functions look like) but it seems like you chose the lucky number, because wikipedia also gives as an example exactly what you asked, and it turns out that the answer is 120 candelas.
