1
\$\begingroup\$

As you may know, I'm working on designing a "lightbox" that will contain 3 high intensity metal halide bulbs - consuming a total of 1600 - 2200 watt. The purpose of the box is to generate ~40,000 lux of light in an area that's 24 inches by 24 inches.

The box is meant to open/close in 1 minute intervals. This will be accomplished through a series of "microcontrollers" and "servo" motors. The box will open from the front (the "door") and be lifted upward through the servo motor.

While the box is closed, no light will be emitted. While it is open, the goal is to cause as much light as possible to escape from the box. For this purpose, another series of "servo" motors will cause the bulbs to move forward slightly out of the box (closer to the subject).

The box will be built out of wood and the dimensions of the box will be about 18 inches, by 12 inches by 12 inches.

This is all background information. My main concern (and the reason for this post) is about "draining" the heat from the box so that the wood doesn't catch on fire.

Currently (based on several suggestions from SO members), I will be taking the following precautions:

  1. I will be placing a 240 CFM fan UNDER the box to filter out the heat.

My question is about this is: How much can I expect the wood to heat up in 1 minute with such a fan present? Furthermore, I want to design the box so it can last for 15 and 30 minute open/close phases as well - how much more would

the wood heat up in 15/30 minutes compared to 1 minute?

If this would present a problem, would using a 400 CFM fan eliminate the problem? If not, would using 1 CFM fan on bottom (of 240 CFM) and another on top (of 100 or 240 CFM), help to enhance air flow and reduce heat in the box?

  1. To protect the wood from heat/fire I plan on spraying No-Heat Spray. Will this help? Is it enough or are there other "coatings" I should apply?

  2. I plan on coating the inside with a mirror like substance to project as much light as possible. Will this cause the wood to absorb more heat or less? (I assume less..)

  3. Is there any other way to "fire proof" the wood (without converting it into metal which would cost $1,000 +) or perhaps my entire design is flawed?

Another question: Part of the plug from the bulb will be inside the box (around 8 inches) - will the heat damage the plug (which will be made from plastic I presume)?

As a side note, someone will be present whenever the bulbs are on so if there is a fire it will be seen. My primary goal is to avoid a fire in the first place but perhaps more importantly I want to avoid significant damage to the wood..

\$\endgroup\$
  • \$\begingroup\$ If the subject is a single point, i'd guess that making a good reflector around your bulbs is more worth than a complicated mechanigal arrangement to move those hot bulbs outside the box. (1.4 J/(g*K) ) * 0.5kg /2000 W - might be the correct formula to calculate how much 0.5kg of wood will heat up if you add 2kW to it - if I'm correct, it'll be 3K per second. \$\endgroup\$ – DThought Mar 16 '15 at 9:12
  • \$\begingroup\$ You might get an improved response if you accepted answers previously given on other questions you have raised on this subject. If the answers were not suitable then state why not. \$\endgroup\$ – Andy aka Mar 16 '15 at 9:12
  • \$\begingroup\$ @DThought - Subject is not a single point. And the wood is atleast 2 inches away from the bulb from all sides so I think formula is incorrect.. \$\endgroup\$ – Michael Morl Mar 16 '15 at 9:18
  • 1
    \$\begingroup\$ You apply 2000Watts of energy to a hollow container... The air inside + the wood outside will take all the energy. Where do you think the energy will go to, if not heating air + wood? What formula would you use? \$\endgroup\$ – DThought Mar 16 '15 at 9:25
  • \$\begingroup\$ Why won't it exit the box through the 240 CFM fan? \$\endgroup\$ – Michael Morl Mar 16 '15 at 9:53