The answer is obviously yes, it's really bad for eyes to read with sad lamps. When you read with sad lamps for a long period of time, you tend to blink less, which will strain your eye muscle and make it ache and even result in dryness of the eyes. In addition, if you read with sad lamps, in order to focus on the object in poor lights, you have to be closer and closer, which might get sore eyeballs, headaches, back and neck aches as well as blurred vision. Therefore, in consideration of your eyes, you'd better read in a good lighting condition. Besides, massaging your eyes when your eyes feel tired is also a great way to protect your vision effectively.
All right, that is a good question, because it is true that we need to take care of our eye health. As a matter of fact, sad lamps could indeed generate some damage to your eye health, leading to a decreased vision, because dim light would make your vision worse and that is the truth. So it would be good for you to get some nice LED that is designed for study purpose. And try to study with right approach and take breaks at intervals.