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lampshadehelmet said:
The venting thing is in a Barry Cooper DVD... What I would be more concerned about with the venting of hot air is that, if you live in a cold area and vent outside, then you are going to have steam flying out of your house in odd places.

In the daytime this can be confusing to people and cause alarm..."where there is smoke there is fire" , well where there is steam venting irregularly, people will draw the same conclusions and bring unwanted attention.

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agmotes165 said:
by using CFL's you are actually generating more heat

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Hmmmm I find that hard to understand

A 250 watt CFL can be touched with the hand yet a 250 watt HPS is absolutely cooking and would burn you if you touched it and they stick out like a sore thumb with thermal imaging cams.

I don't think whatever is generated by a small CFL would be visible.  Especially considering it would be constantly being vented out by cool air.

I spose you mean you have to use many more lights to get the same lumens then that would then increase the heat output by comparison?    I think I get it...

We are talking about 3-4 plants though and were think of using 2 x 250 watt CFLs .  One the flowering type and one the veg type but we just gonna run both through the whole process to get a full spectrum for the whole grow.

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I spose you mean you have to use many more lights to get the same lumens then that would then increase the heat output by comparison?    I think I get it...

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yes, your light conversion efficiency is lower in CFLs than in HIDs, so for 250W of electricity will give you X amount of lumens for CFL's, the same amount of electrical input will give you >X amount of lumens. When you put in 250W of electricity, some of that gets converted into electromagnetic radiation in the form of visible light, and all other types of EMR both above and below the wavelengths of visible light, the infrared radiation will contribute to heat problems, but the rest of the unconverted electricity is dissipated as waste heat from the ballast and through the bulb. So the higher your lumen output per X amount of electricity, the less heat you are going to generate.

The best way I can think to make up an analogy is to think of the light/ballast combo as your body. The electricity going into the system is food. The more efficient your body is at extracting and utilizing calories, the lower the mass of shit is gonna be rejected out of the back end, the shit being the analogy for waste heat. Simple mass balance in this analogy but its the same thing with the lights just an energy balance, which i guess is essentially the same thing and oh I'm rambling now. Sorry for the windy post I'm a little high

anyway, the reason the CFL's are cooler running is just that, they operate at a lower temperature than the HIDs. But if you look at the geometry of the bulb, CFL's have a crapton of surface area to spread that heat over. Total heat transfer is very simply defined as the heat transfer coefficient (U) times the area of heat exchange surface (A) times the temperature difference b/w the surface and the ambient air. This can be a lot more complicated for more exact numerical answers but for this concept simple is better. So assuming that the glass thickness is essentially the same for each bulb type, your U is going to be the same. Therefore if the surface area is way higher in one bulb than the other, then the temperature difference can be a lot lower in the bulb with higher surface area for the same amount of total heat transfer. This is why the surface feels a lot cooler, when in actuality the bulb is dissipating more heat than the higher temperature HID bulb.

Think of the surface area as the cross-sectional area of a pipe. The HID light would be a very small diameter pipe, and the CFL would be a huge diameter pipe. In order to get the same total flow rate through each pipe in gallons per hour, the velocity and thus the pressure difference across the pipe (the amount of push) would need to be much higher in the small diameter pipe than the large diameter pipe. The pressure difference or push in this analogy stands for the temperature difference in each bulb with the ambient air temp.

Okay im done going all crazy with the engineering bullshit...sorry about getting overly excited I love science


Peace and love,
agmotes165