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iglesias@draco.acs.uci.edu, 5/19/00 10:20 -0700, Black vs White Helmet - Thermal Test #2

To: iglesias@draco.acs.uci.edu
From: terry morse <tmorse@terrymorse.com>
Subject: Black vs White Helmet - Thermal Test #2
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Mike-

I thought these test results might be a useful addition to the FAQ:

At the encouragement of others, I ran a more elaborate test to see how black and white helmets react thermally
in sunlight under forced air cooling. This new test aims to answer the question of whether or not a black
helmet is hotter than a white one when worn in direct sunlight, both while at rest and while moving.

First of all, many thanks to Mike of Chain Reaction Bicycles < http://www.chainreactionbicycles.com/> for the
loan of two Trek Vapor helmets for the test. Mike: I'll be returning the helmets (none the worse for wear) very
shortly.

Test equiment:
1 regular household fan
1 150W halogen lamp
1 styrofoam head (from a wig store)
1 handheld anemometer
2 Trek Vapor helmets, size large (1 white, 1 black)
1 digital thermometer
1 stopwatch
( photo: < http://terrymorse.com/bike/imgs/thtest1.jpg> )

Procedure:
Place the temperature probe at the crown of the styrofoam head, and put the helmet on the head. Hang the lamp
5" above the helmet, turn the fan on high speed (6.5 mph), record the temperature every minute until it stops
changing. Set the fan on low speed (5.0 mph), record the temperature every minute until it stops changing. Turn
off the fan, record the temperature until you can no longer stand it. Repeat test for the black helmet, white
helmet, and bare head.

Black helmet test photo:
< http://terrymorse.com/bike/imgs/thtest3.jpg>

Bare head test photo:
< http://terrymorse.com/bike/imgs/thtest2.jpg>

Results:

Complete Results: < http://terrymorse.com/bike/imgs/temps1.jpg>
Air-Cooled Detail: < http://terrymorse.com/bike/imgs/temps2.jpg>

Air Speed | Delta T:Black HemletWhite HelmetBare Head
----------|--------------------------------------------------
6.5 mph|1.4 F1.10.6
5.0|2.51.51.0
0.0 (*)|20.421.129.3
----------|--------------------------------------------------
(*) 16 minutes after turning off fan

As I had expected, there is a measurable difference between the black and the white helmets at these air speeds
and radiant levels.

The temperature rose quickly when the fan was turned off, and it continued to climb for several minutes. There
was no significant difference between the white and black helmet in this "no air" sequence, as the temperature
increased at basically the same rate for both. The small difference between the two might have been caused by a
slight shift in the ambient temperature during the test run. One might conclude that the black surface got
hotter and promoted free convection, which made the black helmet wearer slightly cooler. But I would hate to
conclude that from these small temperature differences.

The bare head test had the greatest and fastest temperature rise in the "no-air" test, even though I had
surrounded the temperature probe with a radiation shield (aluminum foil). While styrofoam certainly is not
thermally equivalent to the human head, this result add credence to the old adage of wearing a hat on a sunny
day (at least when you're not moving).

-terry

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Printed for terry morse <tmorse@terrymorse.com>