You should check the waterproof properties of solar LED street lights by checking the IP rating and components. Firstly, you should check the IP rating of the solar street light. Till now, IP 65 is the best rating, indicating that the light has a qualified performance in resisting water and dust. Secondly, you can check if the sealing at the joints, such as the lampshade, is tight. As for some components, like the solar panels, they have a waterproof design. The chip in the panel is already sealed to resist the water.
More reading: How to Choose All in One Solar Street Lights