looks like you have given a little too much sun, the leaves are turning red. some can handle that pretty well, some get stressed out by it. most i think do well with morning sun, but some shading from direct sun during the hottest part of the day. i'm not an expert on dendrobiums, but the ones i have only bloom at certain times of year, like spring mostly. you can determine their blooming season if you know what species it is, or what makes up its parentage. you may just need to wait until the right season. usually dendrobiums are not blooming due to lack of light, but i don't think that is a problem for you. some (australian ones) also need a rest period, like a cooler, dryer winter to initiate bloom spikes. that might be the problem?