How does that work? Are you using a CD to tell if one fluorescent bulb is better than another? Or to tell if one bulb is LED or incandescent or ...? > Didn't

How does that work? Are you using a CD to tell if one fluorescent bulb is better than another? Or to tell if one bulb is LED or incandescent or ...? > Didn't DIY'ers know this technique for years? I used to live in a rural area (fixing everything in the house by myself) so I'm quite the DIYer but I don't know anything about that!