The equipment and instrumentation used in the study included illuminance and luminance meters (models T-10A and LS-100, respectively, Konica Minolta Sensing Americas, Inc., Ramsey, NJ, USA), a laser distance and angle finder (Bosch model GLM 80), and a reflectance standard (Photo Research model RS-3). The luminaires included (1) area luminaire-1, a commercially available wireless LED area luminaire (although area luminaire-1 is advertised as a “spotlight”), (2) area luminaire-2, a custom-designed LED luminaire, and (3) the LED headlamp (Fig. 2). While area luminaire-1 operates with four D-cell (1.5-V) batteries, area luminaire-2 requires a separate 110-V power supply and the use of an extension cord. Lumen output of the area luminaires corresponded to 400 lm and 663 lm for area luminaire-1 and area luminaire-2, respectively. The mine-issued headlamp (Bushnell model Rubicon H150L LED luminaire) provided the existing task illumination at 173 lm. Other items included adjustable light-weight tripods, aluminum mounting brackets and magnets for positioning and securing the area luminaires, duct tape to tightly secure brackets to a handrail, and rope for hoisting luminaires and brackets to the machine upper deck contiguous with the machine operator cab.

The test luminaires were first mounted to the haul truck, then positioned and secured after obtaining the desired light distribution pattern and area coverage, as follows. For the HTs, both LED luminaires were placed on the handrail or the side of the operator cab near the door of the operator cab and adjusted to avoid shadows from the handrail, deck leading into the cab, or other machine components. This was also the location selected for both FELs. Another location for the luminaires during measurements of the more elaborate ingress/egress system of the newer, larger FEL (CAT 992 K) was the handrail at the mid-location of the deck leading to the operator cab door. Locations for mounting the two luminaires were similar but not identical, owing to the differences in the luminaire design, beam distribution pattern, and mounting brackets. The desired light patterns were visually selected for the areas of interest on the ground and ingress/egress systems. Area luminaire-1 provided a clearly defined circular pattern (Fig. 3) but a smaller area than area luminaire-2. In contrast, area luminaire-2 displayed a somewhat irregular and large elliptical-shaped pattern (Fig. 4). For measurements at the rear of the HTs and FELs, area luminaires were mounted in the vicinity and slightly above the row of lights and reflectors mounted in this location (back-up lights, warning lights, etc.).

Next, the selected tripod, representing the machine operator, was equipped with a mine worker’s hardhat fastened to a rectangular plastic structure that allowed the T10A sensor head to be bolted at the approximate location of the worker’s eye height of 1.7 m (66 in.). The tripod was positioned approximately 1.8 m (72 in.) from the ground at a marked target location and 0.3 m (12 in.) from the first rung of the ladder and on the ground at the driver’s side front tire of the haul truck during pre-shift walkaround at approximately 1.2 m (48 in.) from the sidewall edge of the truck tire (Fig. 5a and b).

The visual targets of interest for the ingress/egress condition (depending on the equipment type included) were the ground below the first rung, the first rung, handrail-left, handrail-right, platform (front edge), platform 2, and first stair step. The newer models of HT and FEL feature the second platform, stairway rung, and extension of the handrail. The tasks comprising the pre-shift walkaround condition included the ground (driver’s-side, front wheel), ground (driver’s-side, mid-truck), ground (driver’s-side, rear wheel), and ground (rear of the truck, 1.2 m [48 in.] out from the rear edge of the tire tread). Photometric, distance, and angular measurements were performed for each of these visual tasks, as follows: task target illuminance (measured directly using the RS-3), distance to the target, linear size of the target, target illuminance at the eye, target luminance, background luminance (an average of 2 to 4 measurements about the target depending on the shape and size), light source illuminance, ambient illuminance, surround illuminance, glare source illuminance at the eye, and angle at the eye between the light source and the target. Measurement units included lux (illuminance), nits (luminance), meters (feet or inches) for linear distance or target size, and degrees (angles). Some angles were obtained directly, whereas others had to be derived from geometric triangular distance measurements. The surround illuminance (Es) was obtained using a baffle arrangement affixed to the T-10A sensor head mounted to the tripod hardhat location that Sammarco et al. used in their lighting study [10]. The baffle, RS-3 reflectance standard, and LS-100 photometer are shown in Fig. 6.

Considering the earlier study [11], the researchers were interested in determining whether adding a simple, inexpensive area LED luminaire and a custom-designed luminaire could improve illuminance levels on and about mobile surface mining equipment during nighttime hours. This would occur when using ingress/egress systems and performing pre-shift walkaround inspections. In view of the IES-recommended illuminance levels for industrial tasks of interest, luminance measurements were made on the visual task target with the LS-100 photometer and the RS-3 reflectance standard. Since the reflectance standard is considered to have a reflective surface of nearly 100%, illuminance is equivalent to luminance given this condition. Thus, in order to obtain illuminance from the measured luminance, one simply multiplies by π to convert from nits to lux, as shown in Eq. 1. This method was utilized in a previous surface mine lighting study by Mayton [14].

where E = illuminance (lux), and L = luminance of the visual task target/object (nits).

To determine values of discomfort glare for the different area luminaires, the objective method was used to predict subjective values that make up the subjective De Boer rating scale. The De Boer method features a nine-point rating scale with odd-numbered verbal descriptors (Fig. 7). It was developed as a qualitative method for estimating discomfort glare from lighting systems [15].

The objective method used to predict the De Boer subjective rating was developed by Bullough et al. [16] and used by Sammarco et al. [6] in earlier mine lighting research. This prediction method employs Eqs. 2 and 3 to obtain the De Boer rating value, as follows: (2) DG=a(log(E1+Es))+b(log(E1/Es))−c(log(Ea))

where

DG discomfort glare;

E_l luminaire source illuminance (in lux);

Es surround illuminance (in lux);

Ea ambient illuminance (in lux).

Coefficients a, b, and c are set at 1.0, 0.6, and 0.5, respectively; (3) DB=6.6−6.4∗log(DG)

where DB = predicted De Boer rating.

As mentioned above, the surround illuminance Es was determined by designing and 3D-printing small baffles of different sizes ranging in diameter from 0.026 to 0.046 m (1–1.8 in.) that slid along a small cantilevered rod 0.18 m (7 in.) in length and 0.0032 m (0.13 in.) in diameter. The baffle allowed a shadow to be cast on the sensor surface in order to measure surround illuminance. A similar reading of ambient illuminance (Ea) was taken without the baffle attached.

Disability glare from the luminaire sources can be determined by calculating veiling luminance. This photometric quantity is used to indicate the extent of the glare issue owing to contrast reduction in the scene being viewed. To calculate the extent of veiling luminance, Eq. 4 was employed to obtain values for the different area luminaires and the visual tasks of interest [17].

where L_v = equivalent veiling luminance in cd/m² (nits); E_o = illuminance from the glare source at the eye in lux; θ = angle between the primary object and the glare source in degrees.

Overall illumination levels with the headlamp were higher than those in the earlier study mentioned above [11]. Measurements using the RS-3 to determine illuminance were taken and available for all but 2 of the 43 ingress/egress and pre-shift walkaround tasks. Figure 8 illustrates the average illuminance levels for the headlamp and the two area luminaires compared with the recommended levels from the IES standard. On average, all luminaires, including the headlamp, provided adequate illumination.

Figure 9 displays the results for the ingress/egress visual tasks for all four machines. Considering the newer Komatsu haul truck (Fig. 9a), the De Boer ratings for area luminaire-1 show better results for all eight tasks and lower glare compared with area luminaire-2. The ratings for area luminaire-2 varied from a low of 4 to a high of 5, in contrast to area luminaire-1 ratings, which show a low of 6 and a high greater than 8. Figure 10a displays the predicted De Boer ratings for pre-shift walkaround tasks for the newer Komatsu haul truck. Area luminaire-1 results indicate lower discomfort glare values relative to area luminaire-2 at the driver’s side and rear areas for the pre-shift walkaround visual tasks. In Figs. 9b and 10b, glare values for the 777D haul truck show little difference between the two area luminaires for the ingress/egress tasks, and slightly better values for area luminaire-1 in the walkaround tasks.

Regarding the results (Fig. 9c) for the CAT 992 K wheel loader, the ingress/egress tasks showed slightly better values again for area luminaire-1, with a median value of 6 (one unit between satisfactory and just permissible) versus 5 (just permissible) for area luminaire-2. The walkaround tasks (Fig. 10c) showed dramatically lower glare (higher values) for area luminaire-1, ranging from between just noticeable and satisfactory to 7 units above just noticeable. This contrasted with area luminaire-2, which showed values ranging from just permissible to satisfactory. Similarly, the CAT 980C wheel loader results (Fig. 9d) for ingress/egress tasks showed only slightly better values again for area luminaire-1 versus area luminaire-2 for the front driver’s side tire location and the midpoint between the front and rear tires. Other task location values were the same, with a median value of 4, which is between just permissible and disturbing. On the other hand, the walkaround tasks (Fig. 10d) showed dramatically lower glare (higher values) for area luminaire-1 ranging from 8 to 10, one to three units above satisfactory, versus 7, satisfactory, for area luminaire-2.

Concerning veiling luminance or disability glare, the data showed distinct differences in veiling luminance values for area luminaire-1 versus area luminaire-2. Depending on the visual task, the equipment, and the activity, the current available data illustrate that for most of the tasks, area luminaire-1 performs significantly better with regard to veiling luminance or disability glare. Eighty-six percent of the 43 tasks evaluated showed area luminaire-1 with lower levels of veiling luminance or overall better performance. There were three instances where area luminaire-1 did not show better veiling luminance. One was at the driver’s side rear tire for the Komatsu HD785 (Fig. 12a). The other two were platform 1 (Fig. 11b) and the driver’s side forward tire for the CAT 777D (Fig. 12b). Moreover, we observed instances where veiling reflections occurred during measurements of the handrails. Veiling luminance values varied from about 1 nit to 643 nits for area luminaire-1 versus 4 nits to 616 nits for area luminaire-2; the median values for the same luminaires were 14 nits and 80 nits, respectively. The average veiling luminance values with standard deviations were 75 ± 138 nits for area luminaire-1 and 178 ± 203 nits for area luminaire-2. Figures 11 and 12 illustrate differences in log veiling luminance for the two area luminaires and all four machines during ingress/egress tasks and during pre-shift walkaround tasks, respectively.

The testing in this study was conducted using a limited number of equipment types and ingress/egress system designs. Placement of the area luminaires was not always optimal, owing to the design features of the equipment and luminaire mounting devices available. The Sammarco study [10] employed neutral density filters to reduce the light output of area luminaire-2 by a factor of 25% and 50% in the underground miner roof bolter study. In the present study, time constraints and mounting challenges did not permit an evaluation of area luminaire-2 using neutral density filters, and there was insufficient time for walkaround measurements on the passenger side of the vehicles studied. Nevertheless, we believe that similarities to the ground surface and vehicle components on the opposite side of the vehicles and similar luminaire mounting locations would yield results similar to those for the driver’s/operator’s side of the vehicle. Moreover, measurements of the area luminaires without the headlamp task lighting were initially considered, but it was determined that they did not accurately reflect actual mining conditions and activities, and also required more time than was available. The absence of this data was deemed to have little effect on the study findings in view of the reported data. Tests could not account for the likely accumulation of dust, dirt, or other debris that may occur during actual mining operations.