Flourescents - Color shift

[georgiajams]

So, we heard from Dr. Joshi that, in his testing, the only "spectrum shift" he has logged with MH bulbs is a downward trend (e.g. less PAR, not right/left color shifting).

Just wanted someone to clarify something. With respect to fluorescent bulbs (not Metal Halide), has there been studies that indicate an actual color shift actually happens, or is this more marketing hype to get us to buy more bulbs? If they do shift, could this be yet another advantage of MH over fluourescent lighting?

[kpatterson]

I believe that Dr. Joshi showed graphs which explained the 'color shift' of aging lamps. Not only does the overall PAR decrease, but different wavelengths of radiation decreased at different rates. The blue end of the spectrum decreased more rapidly than the red end, so you do perceive a 'color shift' due to less blue light being generated (the color tends to become more green/yellow).

[georgiajams]

you do perceive a 'color shift' due to less blue light being generated

True, glad you clarified that. I guess what I was highlighting is that his studies on MH bulbs indicate that the spectrum doesn't shift left/right such that the light generated is outside the usable spectrum for corals (or may fuel algae growth). Rather, the "area under the curve" merely drops (at different rates at different wavelengths).

As you are alluding to, one of the conclusions made is that if your MH bulb starts out more blue (e.g. a 20K/bluer bulb), the more PAR you will lose over time, generally speaking.

I'm wondering if fluorescent bulbs behave similarly, or do they shift into some different spectrum such that they are no longer useful to corals and/or fuel algae growth, as often repeated.