Be careful when using transparencies. Use an opaque material whenever possible. On mobile platforms, avoid using transparency unless it is necessary.
Rendering an object with transparency always uses more GPU resources than rendering an opaque object. Using many transparent objects can affect performance on mobile platforms. Performance can be a particular problem when transparent objects are rendered on top of one another multiple times.
When the same pixel is drawn on-screen multiple times it is known as overdraw. Overdraw is a problem because the more layers of transparency that you have, the more expensive the rendering becomes. For mobile platforms, overdraw can severely affect performance.
The following screenshot shows how the blue lights could have had a transparency effect, but they still look good with an opaque material:
When building levels, try to keep overdraw to a minimum. Unity lets you measure and visualize the amount of overdraw that is in a scene. This mode is highlighted in the following screenshot: