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Join Date: Feb 2007
Posts: 2

Heat Lamps to generate solar radiation?

02/18/2007 11:17 PM

Hi All,

I want to perform a temperature rise test on an outdoor electrical enclosure (stainless steel)

The test will be indoors in a room with no air flow. I would like to simulate the solar radiation (to our rating of 1100W/m2) by using a heat lamp (the sort that is used in the bathroom).

The questions I have are:

- Is a heat lamp a suitable method of simulating solar radiation or are there better options?

- What is the efficiency of a heat lamp. (ie: if I need 200W of heat, what size heat lamp would I require)

- What is the throw angle of these lamps? Is it included in the manufacturers specification?

Any help with this issue would be greatly appreciated!

Hank.

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Join Date: Nov 2006
Location: Bay Shore, NY
Posts: 715
#1

Re: Heat Lamps to generate solar radiation?

02/19/2007 8:29 AM

Hank,

"- Is a heat lamp a suitable method of simulating solar radiation or are there better options?"

Answer: NO it is not. I am not aware of any means to reliably equate the effect of infrared radiation to solar radiation for your purposes. Either perform the test in actual sunlight or go through the steps necessary to perform an accurate test indoors with artificial illumination.

Therefore, skipping over any details related to heat lamps, I simply would NOT use them for your test.

When structuring tests, it is of the utmost importance to determine exactly what the goal is, what are your controls (independent variables) and what you want to measure (dependent variables) and how you can measure it. You want to set up the test in such a way that you can get repeatable results, and document every aspect of the setup and conditions (including photographs) for later reference. This last step is important both from the standpoint of verification, and to accumulate meaningful data that will likely find use over time in making estimates or validating the potential use of scale models at some point.

If I understand you correctly, you want to simulate and measure the temperature rise, above various ambient temperatures in still air, of a "bare surface" stainless steel electrical cabinet exposed to sunlight (solar radiation to your rating of 1100 W/m2). You make no mention of any heat loads from the electrical equipment/circuits inside the box, so I am left guessing as to the exact wording and context of your aforementioned rating.

That exact definition and specified or implied parameters of your rating is of the utmost importance here since that is what you are to measure against. The amount (and wavelength) of reflected radiation striking the enclosure on the surfaces not exposed to direct sunlight will also affect your results.

Since solar radiation is of a broad spectrum and various wavelengths will be absorbed / reflected differently by the surface of your enclosure, the proper test would require a light source(s) with the equivalent spectrum of sunlight. The color temperature of the light can be used as a good guide, and you would be looking for light in the range of 5200-6000 Kelvin.

http://photo.net/learn/optics/edscott/cf000030.htm

Some research on your part will be required, to help determine what type of lights will best fill your needs, but some type of xenon lamps are a good bet, and this link is one example:

http://www.pti-nj.com/obb_lamps.html

The light source(s) should be arranged to approximate the effect of a "distant" point source (like the sun), rather than illuminating the enclosure from a variety of directions or from a point source too close. Due to the "inverse square law", depending on the size of your enclosure, you will need a lot of lighting power to achieve the 1100 W/m2 intensity at the surfaces.

You will require a light meter accurate for measuring the intensity of "sunlight" that you can use to measure the intensity of light just above the surface of the enclosure since "throw angle" or other means of potential calculation will not yield any accurate information. I would also measure and record color temperature as part of the data.

You will also want a contact thermometer to measure points on the enclosure during the tests. Make some type of marks on various points on all exterior surfaces of the enclosure so that successive measurements are made at the same locations. Take the additional time to set up a clear and referenced data sheet on which to record your results so that you can map the temperature measurements to their location on the enclosure, the time they were taken, the concurrent internal heat load from components (if any) based on the wattage, and ambient room conditions.

Your "rating" should define exactly how the temperature rise is measured, and no matter what other measurements you make, make sure you get those. In practice, the actual running of this type of test is trivial compared to the setup time and effort, so it makes sense to take as much data as possible. Even though you see no need for the additional data at the time, some questions will inevitably arise after the test has been dismantled.

Since in the real world, we are not always able to do things the way they ideally should be done, keep in mind that the accuracy (or lack thereof) your test achieves is the direct result of the care and effort you put into it. This is a decision only you (or your company) can make, based on how important the results are, and the potential consequences of a mistake or an erroneous approval.

I hope this was of some help to you. Feel free to contact me with any questions.

Greg

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