Whilst we can agree about the literal meaning of frosted and unfrosted, the important part is what the significance would be in this context.
We need to look at the properties of these bulbs. Both lampshades and frosting made the light less harsh by making the shadows more diffuse. A lampshade would have given the most pleasant light, at the cost of (1) the lampshade, and (2) reduced efficiency as some light would be absorbed, leading to higher running costs. A frosted bulb would have had the same two effects, to a lesser extent.
This bulb (which clearly had no shade as it was just on a wire) was therefore the cheapest option, in terms of both capital and running costs. So we get a sense of cheapness.
But we also get a sense of atmosphere, as these moving shadows, caused by the swinging bulb would have been much more noticeable, detailed and distracting from this unshaded, unfrosted bulb. Even a small movement would lead to moving sharp patterns on the wall, that would not occur with a frosted bulb.
Addition in response to comment: since the bulb is in a tent it is quite possible it is battery powered. This would accentuate the power-saving aspect. Further, a low-powered bulb is likely. This would have had a physically smaller filament and made the shadows even sharper. Since everything would be close together, it would be easy to see a lot of detail, even fingers and locks of hair in the moving shadows on the walls of the tent.