T5HO Cold Spot Temp vs. PAR output

[xmas_one]

Yesterday I was watching a BRS video on T5HO lighting, towards the end of the video he was talking about bulb efficiency and the effect fan speed can have on the bulb's output.

 

 

I was curious and PAR tested my 4x24w ATI Sunpower at all available fan voltages (3, 4.5, 6, 7.5, 9, and 12) with and without the splashguard. The PAR readings were taken 3 minutes after voltage changes to ensure the temperature would have time to settle. Room temperature was measured at 74F.

 

 

Everything I have read tends to suggest that there is an optimal "lamp cold spot" temperature in which the bulbs are most efficient, and that once you exceed that temperature the efficiency begins to drop again. For all of the fan settings, 3V gave the highest PAR readings, possibly a slower fan would have produced an even higher PAR number. I did also test both with and without the shield with the fans off to see if the shield transparency was cause for the nearly 10% gain in PAR numbers at all voltages, but it was the same at 108. This would suggest that the wall temps of the bulbs are also a factor just like in the BRS video.

Page two of the following PDF suggests the optimal operating temp for the cold spot to be 118F.

http://lumenoptix.com/uploads/HowtoDesignBetter_lowres.pdf

 

[gus6464]

BRS got the most PAR with fan at 6v and no splash guard.

[evilc66]

It's been a while since this has been brought up, but last time it was more to do with metal halide. The same concept applies though. Back then, everyone was talking about how they can reduce tank temperatures by cooling the bulb directly, but no one appreciated that the bulb needed to operate at a certain temperature. Oddly enough, the same mercury "cool spot" exists in halides as well as fluorescents.

 

With T5 though, you have another element that does require cooling, and that's the phosphor. Make the phosphor cooler, and you can extend the effective life of the bulb. Is that an appropriate trade off for lower PAR numbers? Could be.

[davy jones]

Id be interested in hearing others tests with this as well (also saw the brs video which piqued my interested)

[xmas_one]

It's been a while since this has been brought up, but last time it was more to do with metal halide. The same concept applies though. Back then, everyone was talking about how they can reduce tank temperatures by cooling the bulb directly, but no one appreciated that the bulb needed to operate at a certain temperature. Oddly enough, the same mercury "cool spot" exists in halides as well as fluorescents.

 

With T5 though, you have another element that does require cooling, and that's the phosphor. Make the phosphor cooler, and you can extend the effective life of the bulb. Is that an appropriate trade off for lower PAR numbers? Could be.

Bulb life vs temp seems like an inevitable trade off, but I haven't been able to find any solid info linking lower bulb temps to extended bulb life. Anything I've seen talking about bulb life just relates to power cycling (on/off) diminishing the life span. Do you have any links/info that shows higher bulb temps lowering bulb life? Thanks for your input, it is much appreciated!

[evilc66]

I don't have any articles explaining this. If I find anything, I'll post it.

 

Power cycling will always have the biggest effect on bulb life, as it directly affects the electrodes at each end of the bulb. The type of ballast used plays a big role in this.