Phase 1
Independent variables
Phase 1 consisted of a 3 x 2 x 2 repeated measures design (each subject experienced all
levels of the three independent variables, resulting in 12 experimental conditions per subject).
Independent variables included IRR treatment, air temperature, and repetition. Levels of air
temperature were blocked between subjects, and trial repetitions were randomized within
subjects.
IRR treatment. Layers of an aftermarket IRR film were draped—alternating between one
layer of treatment, two layers of treatment, and no treatment—over the driver-side window of the
research vehicle. Specifications of the film and the method of application are described later in
this section.
Air temperature. Air temperature was an average measurement of four sites within the
vehicle cabin (described later in this section). Air temperature was held approximately constant
at two different levels (75° F and 90° F [23.9° C and 32.2° C]) by a combination of the vehicle’s
A/C system and two portable electric heaters.
Repetition. Every subject experienced two repetitions of each combination of air
temperature level and IRR treatment level.
Dependent variables
Objective measures. Objective measures for Phase 1 included skin temperature and total
solar irradiance. Skin temperature was an average measurement, weighted according to relative
surface area of skin, of four different locations on the body: neck, right scapula, left hand, and
right shin (ISO 9886, 1992). Downward total solar irradiance was measured at two sites: the roof
of the car (ambient measurement) and the driver-side window ledge (irradiance reaching the
subject). (Irradiance reaching the subject—after reductions from the car’s glazing and the IRR
treatment—is referred to as net irradiance throughout the remainder of this report.)
Phase 1
Independent variables
Phase 1 consisted of a 3 x 2 x 2 repeated measures design (each subject experienced all
levels of the three independent variables, resulting in 12 experimental conditions per subject).
Independent variables included IRR treatment, air temperature, and repetition. Levels of air
temperature were blocked between subjects, and trial repetitions were randomized within
subjects.
IRR treatment. Layers of an aftermarket IRR film were draped—alternating between one
layer of treatment, two layers of treatment, and no treatment—over the driver-side window of the
research vehicle. Specifications of the film and the method of application are described later in
this section.
Air temperature. Air temperature was an average measurement of four sites within the
vehicle cabin (described later in this section). Air temperature was held approximately constant
at two different levels (75° F and 90° F [23.9° C and 32.2° C]) by a combination of the vehicle’s
A/C system and two portable electric heaters.
Repetition. Every subject experienced two repetitions of each combination of air
temperature level and IRR treatment level.
Dependent variables
Objective measures. Objective measures for Phase 1 included skin temperature and total
solar irradiance. Skin temperature was an average measurement, weighted according to relative
surface area of skin, of four different locations on the body: neck, right scapula, left hand, and
right shin (ISO 9886, 1992). Downward total solar irradiance was measured at two sites: the roof
of the car (ambient measurement) and the driver-side window ledge (irradiance reaching the
subject). (Irradiance reaching the subject—after reductions from the car’s glazing and the IRR
treatment—is referred to as net irradiance throughout the remainder of this report.)
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