Bonsai needs all the light it can have. The more exposure to light, the healthier the bonsai, and the smaller the leaves of the Bonsai. A glass by itself only refracts (change direction of) light and not concentrate light as it is in a lens. The heat that people feel behind a glass in a closed room or inside a parked car under the sun is more of a green house effect rather than burning. The green house effect only elevates the temperature because of