Dendrobium nobile with black spots

[master_xelis]

One month ago I bought this Dendrobium nobile. It has been in the outside of the house. Weather here in Mexico has been cold (about 14° C in the day and 6° C in the night), also it's been raining. The exception was last week in which there was a heater weather.
About a week ago I noticed some black spots in the base of the leaves of the Dendrobium. I have no idea why.
It has been in a place with shadow, but I read that Dendrobiums need some Sun during Winter, that's the reason why I changed the place to a one with better sunlight, but not really direct sunlight. It is behing a rose plant.
If some of you know the reason of the spots and what to do, let me know.
Photos are below:








Update (011514):
Sonya asked me if the canes are firm where the dark patches are, and that's true.
At the time I went to confirm this, I noticed that a leave has a white spot and that there is a new cane growing but with a very white color.
I think that the white spot is because of a sunburn, right?
Is the color of the new growth normal?

Photos:

[WhiteRabbit]

Some (leaf and sheathy material around the cane) might be natural and age related. The dark area at the tip of the cane might be from stronger light ...

Are the canes firm where the dark patches are?

[master_xelis]

Yes, canes are firm in those places.

[WhiteRabbit]

Photo #3 - I cannot tell ... is the pbulb split there in the dark area?

[master_xelis]

No, it is not split. It is dark but there's no damage on the pbulb.

[WhiteRabbit]

I'd watch it, but it's likely not cause for concern if those areas are firm.

[master_xelis]

That's great! What do you think about the color of the little new growth?

[WhiteRabbit]

I think it looks ok