“…As in, the economy bulbs?”
Just to clarify, I’m assuming you are asking why insects are drawn to lights like LED/economy light bulbs, despite the fact that they give out relatively low UV rays? (I believe the insects you’re referring to are one’s such as moths, which are attracted to bright lights–rather than, say, mosquitoes which are drawn to heat.)
In this case, the answer is that these kinds of insects are attracted to UV light, which they are able to see. But they are also attracted to blue light. They pretty much avoid red light and are rarely attracted to heat.
(If you wanna get reeeaallly specific, this is called “positive phototaxis” and is caused by unnatural sources of light which interfere with their internal navigation systems. Before the introduction of artificial lights, nocturnal insects such as most moths evolved to use natural light sources such as the moon or stars. Many other day time/evening insects forage at twilight when blue light dominates the irradiance spectrum of the sky. When they pass artificial light they are unable to stay aligned and circle round it or fly into it.)
Anyway, what it boils down to is that while most LED lights do not produce a significant amount of UV light, they do produce blue light. (That’s one reason why “bug zapper” lights are so blue – insects are uncontrollably drawn to that color range.)