Cloud computing has become prevalent in the sharing of outsourced data because of its strong computing power and storage capacity. Ensuring data security is vitally important for data sharing in clouds. Recently, numerous broadcast proxy re-encryption (BPRE) schemes have been designed to solve the data security issues of such applications. But no BPRE schemes are designed to resolve the issues of re-encryption key updating for data sharing in a dynamic cloud environment. Therefore, we put forward a lightweight dynamic broadcast proxy re-encryption scheme (LD-BPRE) to resolve the above-mentioned issue in dynamic settings in which the data owner can dynamically change a group of data users and he/she does not need to update the re-encryption key for a new set of data users. That is, the proxy can re-set a re-encryption ciphertext for a new set of delegatees using the original re-encryption key. It is significant in a dynamic cloud setting and causes convenience for cloud users. LD-BPRE is lightweight for the user with low-power devices because most computing overhead is offloaded to the clouds. We formally provide the definition for LD-BPRE and prove its security under a decision n-BDHE assumption without the random oracle. Finally, extensive comparisons and experiments indicate that LD-BPRE is efficient and practical.