Sometimes when your bulbs are getting old it's tough to tell. Here's a quick and dirty set of instructions that should help you determine if you need to replace them (provided you have Photoshop). This will probably work with MH as well, but I tested this on T5's. 1. Take a picture of your lighting ballast. for your reference, from left to right lit bulbs are: 10K daylight old 10K daylight less than 3 weeks old 10K daylight old old acitinic. 2. In photoshop, go to layers->new adjustment layer->color balance. 3. Add a new red layer with darken, click ok. 4. Set shadows, midtones, and highlights all to 100% for Cyan. 5. Apply, you should now bring out all the red wavelengths that your camera has picked up: As you can clearly see, I need to replace the 1st bulb badly, while the new bulb looks fine, and the 3rd bulb is starting to get red. Hope this helps anyone that thinks they may need to replace lights but isn't sure.