You said it was in an opaque container and further with a bag and also not in direct sunlight, so it should be fine. While others are right in that moisture is primarily the concern, it is a little inacurate of others to say light is not a problem at all. It should absolutely be stored in a cool, dark place out of direct sunlight.
UV radiation can initiate photochemical reactions that lead to the degradation of SN as sunlight, particularly in the UVA and UVB ranges (SN absorbs UV radiation primarily in the 200-300 nm range). The reason is light can excite the nitrite ion which can absorb light in that range and bonds between nitrogen and oxygen in the nitrite ion to weaken, leading to the formation of nitrogen dioxide and other similar reactive intermediates. This process then generate free radicals that further react with SN ultimately leading to oxidation-reduction into nitrate. But yes that risk is heightened in the presence of other substances (such as moisture). It should not be stored in direct sunlight.
I doubt the electric lights you have emit light in the UVB range that would be measurable enough to effect it: fluorescent lights do produce some UVB radiation, incandescent produce very little and LED don't really produce any that would be of risk for SN. I do not think it is rise for much worry.
Even if it was in direct sunlight, if it was sealed and airtight it should not degrade that quickly for it to be a concern especially in absence of moisture. If you are truly concerned, it would be worth testing it before use but I think it would pretty unlikely it degraded that much, that quick, especially because here you said it wasn't direct sunlight anyways.
Hope you find everything you are looking for and get whatever peace & serenity you seek.