The effect of cap lamp lighting on postural control and stability

John J. Sammarco ,1 * , Jonisha P. Pollard 1, William L. Porter 1, Patrick G. Dempsey 1, Caitlin T. Moore 1

*	 Corresponding author. Tel.: þ1 412 386 4507; fax: þ1 412 386 6710.
 

E-mail address: JSammarco@cdc.gov (J.J. Sammarco).
 1 Disclaimer: Mention of any company or product does not constitute endorsement by the National Institute for Occupational Safety and Health. The findings and

conclusions in this report are those of the authors and do not necessarily represent

the views of the National Institute for Occupational Safety and Health.

Office of Mine Safety and Health Research, National Institute for Occupational Safety and Health, 626 Cochrans Mill Rd, PO Box 18070, Pittsburgh, PA 15236, USA

abstract

Researchers at the National Institute for Occupational Safety and Health (NIOSH) are conducting mine

illumination research with the objective of improving miner safety. Slips, trips, and falls (STFs) are the

second leading accident class (18.1%, n 1⁄4 2,374) of nonfatal lost-time injuries at underground mines

(MSHA, 2005e2009). Factors contributing to STFs include recognition of hazards as well as postural

balance and age. Improved lighting may enable better hazard recognition and reduce the impact of

postural balance and age. Previous research has shown that cap lamp technology that used light-emitting

diodes (LEDs) has improved hazard detection. This study was an initial investigation to determine if cap

lamp lighting significantly influences measures of static postural stability (displacement and velocity of

center of pressure). Results of this investigation showed no significant differences in the balance

measures of interest between cap lamps tested. However, balance was shown to significantly decline

(p < 0.05) when tested in an underground coal mine compared to the laboratory testing condition.

Relevance to industry: Underground coal mine workers wear cap lamps on their hard hats as their

primary light source to illuminate nearby areas where their vision is directed. Proper illumination may

improve miner safety by improving their STF hazard recognition and balance.

1. Introduction

Approximately 619,000 people are employed, directly and

indirectly, in the United States mining industry (BLS, 2009).

Underground coal mining involves a hazardous, dynamic environment that includes dust, confined spaces, low reflective surfaces,

low visual contrasts, and glare. The Illuminating Engineering

Society of North America cites the working face of an underground

coal mine as the most difficult environment in the world to illuminate (Rea, 2000). Mine workers depend on illumination for

virtually every aspect of performing their jobs as well as for seeing

various mining hazards. Equipment-related injuries where illumination can be a factor include pinning/striking accidents involving

moving equipment, slips and falls during equipment ingress/egress,

and accidents during maintenance and repair activities.

Mine Safety and Health Administration (MSHA) accident data

for 2005e2009 indicates that STFs are the second leading accident

class (18.1%, n 1⁄4 2,374) of nonfatal lost-time injuries at underground mining work locations. During this period, STFs resulted in

149,002 total days lost from work (MSHA, 2005e2009). STF injuries

have also plagued British coal mines in recent decades. Foster

(1997) examined injuries from the British Coal Midland’s Group

underground coal mining accident database for 1988 to 1994.

Foster concluded that STF injuries occurred more frequently than

any other accident category. He suggested that better lighting could

reduce the risk of STF injuries. Odendall (1996) examined accidents

at South African gold and platinum mines and established that

a strong relationship existed between the levels of illumination and

the number of accidents. Research, specific to the lighting of

underground metal/nonmetal mines, determined that increasing

the illuminance could improve visual performance for detection

and recognition of trip hazards (Merritt et al., 1983).

There are scant detailed mining injury data concerning STFs

where illumination was a factor. One reason, in relation to U.S.

mining accidents, might be that the MSHA accident database has

several limitations. For instance, when reporting an injury, none of

the 12 accident/injury codes from which mine operators may

select include illumination or miner visual performance. Further,

when given the opportunity to provide a narrative, the causes

identified for the mine operator’s consideration are mining

equipment, protective items, compliance issues with rules and

regulations, and operator issues such as job skills, training, and

attitude. Thus, mine illumination is not specifically mentioned nor

implied as a cause or condition from which to select or describe

when reporting an injury.
Lighting can influence the performance of people in the industrial workplace by way of ten mechanisms that include visual

performance, visual comfort, visual ambience, interpersonal relationships, job satisfaction, and problem solving (Juslén and Tenner,

2005), Poor lighting and reduced visual feedback decreases detection of STF hazards and has also been shown to decrease postural

stability, increasing one’s risks for falls. Brooke-Wavell et al. (2002)

studied the effect of lighting on the postural sway of healthy older

women. Subjects were asked to perform quiet standing in five

environmental conditions while center of pressure (COP)

measurements were taken. These conditions were normal laboratory lighting (186 lx), moderate lighting (10 lx), dim lighting (1 lx),

eyes closed, and with a repeating pattern projected on the walls.

Results showed that anteroposterior sway was significantly greater

when standing with eyes closed than any other condition. It was

also greater in dim lighting than moderate or normal lighting.

Simeonov and Hsiao (2001) found that providing roofers with

a close visual reference significantly decreased area of sway

indicative of improved postural stability while standing on an

elevated platform. Without close visual reference, the velocity of

sway increased 17% when subjects were standing 3 m above the

ground on a firm surface and 21% when subjects were standing 9 m

above the ground on a firm surface (Simeonov and Hsiao, 2001).

Age has also been associated with increased postural sway.

Previous research has noted decreased visual performance and

decreased postural control were detected as early as 40 years of age

(Era et al., 1986; Howarth, 2006). Visual changes with age include

the decline of the ability to focus on near objects (presbyopia) and

the yellowing of the lens, which results in decreased contrast

sensitivity (Howarth, 2006). During walking, visual cues are integrated with the somatosensory and vestibular systems to maintain

balance. With age, the quality of these visual cues decline and may

contribute to increased risks for falls. Additional deteriorations in

proprioception, reaction time, and muscle strength contribute to

these risks and may be apparent as early as 40 years (Era et al.,

1986). The authors also noted a more pronounced rate of decline

in male subjects. The reduced balance in older age may be attributed to many factors including loss of receptor cells in the

vestibular organ, reduced peripheral sensation, and changes in

visual function (Brocklehurst et al., 1982; Lord et al., 1991;

Rosenhall, 1973). Of these factors, deterioration in visual function

may be compensated for by improving the quality of lighting. There

is an additional need for improved lighting due to the increasing

age of the mining industry, whose median age is 45 years.

Various types of lighting are used to provide illumination for

underground mines. Underground mine workers wear cap lamps

on their hard hats to illuminate nearby areas where their vision is

directed. The main parts of a typical cap lamp are the headpiece,

battery, and an interconnecting cable. The headpiece contains the

light source and is mounted on the miner’s protective helmet. Cap

lamps are often a mine worker’s primary source of light needed to

safely perform their job tasks and to visually detect hazards from

moving equipment or to visually detect STF hazards on the mine

floor (Cornelius et al., 1998). Visual detection is very important

given that, some research results have indicated that reactions to

visual signals are generally faster than those for auditory signals

(Fion Lee and Alan Chan, 2007). Therefore, the quality and quantity

of illumination are critical factors for mine workers to perform their

jobs safely (Sanders and Peay, 1998). Traditionally, miner cap lamps

used an incandescent bulb as the light source and a lead-acid

battery. Today, LED light sources and lithium-ion batteries are

gaining acceptance. Newer cap lamps are integrating the battery

into the headpiece.

Previous underground mining research has shown that

improving light quality decreases mining accidents by enhancing

visual performance in the detection and recognition of STF hazards

(Daly, 2001; Merritt et al., 1983). Most recently, the importance of

human factors in the design of mining equipment was detailed by

Horberry et al. (2011), where an entire book chapter was devoted

to visual performance and the illumination of the mining

environment. The cap lamp is an important piece of personal

protection equipment in mining. Therefore, to enhance the safety

at underground coal mines, NIOSH researchers have focused on

developing a new LED cap lamp to improve the ability of miners to

detect hazards. Historically, light beams from cap lamps have been

a tightly focused (6e10°) symmetrical spot that is very similar to

a flashlightda design approach unchanged since the 1914 Edison

cap lamp. Thus, traditional cap lamps create a “tunnel vision” type

of visual environment where the floor is poorly illuminated and

visual cues about the geometry of the mine are very limited. NIOSH

researchers developed a new approach by using multiple LEDs and

specialized optics to direct lighting to better illuminate STF

hazards and moving machinery hazards. Human subject data

indicate a 79% improvement in detecting moving hazards in the

peripheral field of view and a 194% improvement in detecting STF

hazards (Reyes et al., 2011).

Decreased visual performance and postural stability are associated with poor lighting as well as increased age (Brooke-Wavell

et al., 2002; Daly, 2001; Merritt et al., 1983; Brocklehurst et al.,

1982; Lord et al., 1991; Rosenhall, 1973). These factors likely

contribute to the magnitude of STF accidents in the underground

mining population. However, the influence of cap lamps on

postural stability has not specifically been investigated. Although

the LED-based cap lamps have been shown to improve STF hazard

and peripheral motion detection, the effects of cap lamp design (if

any) on postural stability are unknown. The primary objective of

this study was to determine if cap lamp design affects postural

stability. A secondary objective was to determine if age is a factor.

2. Materials and methods

2.1. Subjects

Employees at the Bruceton, PA, location of NIOSH were

recruited to be subjects. Subjects signed an informed consent form

and were instructed about their right to withdraw freely from the

research at any time without penalty. The protocol was approved

by the NIOSH Human Subjects Review Board. None of the subjects

were specifically involved with this cap lamp research, and most

of the subjects were not familiar with miner cap lamps or had only

used them infrequently. Subjects with radial keratotomy,

monocular vision, glaucoma, or macular degeneration were

excluded. Only the subjects that passed vision tests for. Snellen

distance visual acuity of 20/40 or better, Mars Letter contrast

sensitivity of 1.72e1.92 values of log contrast sensitivity, and

peripheral vision of at least 80° for each eye were accepted for

the study. Subjects having a balance disorder were also excluded

as determined by a screening questionnaire and balance

screening tests. The balance screening tests consisted of

horizontal gaze nystagmus, walk and turn, one-leg stand, and

Romberg tests (Khasnis and Gokula, 2003; Tharp et al., 1981).

All balance screenings were administered and scored by one

researcher given the subjective nature of the tests. Following

successful completion of the functional balance screening, baseline

balance measurements were collected using a force plate. Balance

screening and baseline testing were conducted under normal

lighting conditions.

Thirty-one subjects participated: 23 male and eight female.

There were 10 subjects each in the age groups of younger (18e25

years), middle (40e50 years), and older (51þ years). The average
ages were 21.1 yrs, 44.8 yrs, and 55.6 yrs respectively. The age group

from 26 to 39 years was not used because there are generally

minimal changes in vision for those ages (Blanco et al., 2005).

The average subject age was 40.5 yrs which is representative of the

average U.S. mine worker’s age of 41.8 yrs (BLS, 2009). All but one

subject completed the testing. That subject withdrew because of

nausea experienced during testing.

2.2. Experimental design

A 3 x 2 x 3 (3 age groups, 2 visual reference scenarios, 3 cap

lamps) repeated-measures randomized complete block analysis of

variance (ANOVA) experimental design was used. The

presentation of the six combinations of visual reference and cap

lamp conditions was randomized for each subject. Age was treated

as a nested-within-subjects variable. PROC GLM of SAS 9.2 was

used for analysis of the ANOVA, with the RANDOM statement to

indicate that the subject was nested within age categories. Type III

sums of squares were used for the F-tests. Tukey’s studentized

range test was used (via MEANS option) for post hoc mean

comparisons of significant factors. Separate ANOVAs were run for

each dependent variable: center of pressure (COP) velocity in the

mediolateral (CPVML) and anteroposterior (CPVAP) directions, the

root mean square (RMS) of the COP displacement in the ML

(RMSML) and AP (RMSAP) directions, and the sway area (SA).

Because the baseline measure was taken in a laboratory with

a fixed visual reference, the baseline measure could not be added as

a condition to compare to the cap lamp conditions. In order to

compare the baseline to the cap lamps, a 3 x 4 (3 age groups, 4

lighting conditions) ANOVA was run with the baseline condition

and the near conditions for each of the three cap lamps together

forming the four lighting conditions. The near condition was

chosen since this was closest to the laboratory setup distance from

the forceplate to the wall that the subjects faced. This ANOVA

allowed for comparison of the baseline conditions to underground

conditions to determine if underground conditions lead to reduced

postural stability. The analysis and SAS options were the same as

discussed in the previous paragraph. Finally, correlations between

the dependent measures and age were calculated for the baseline

condition for reference comparison to findings in the literature.

3. Experiment layout and apparatus

3.1. Safety Research Coal Mine (SRCM)

This study was conducted in the NIOSH Safety Research Coal

Mine (SRCM). The SRCM is located on-site at the Bruceton, PA,

NIOSH campus and it has been used for decades by researchers to

conduct experiments in a realistic coal mine setting. The SRCM is

inactive in that no coal is mined; however, typical mine lighting and

ventilation conditions are present. The entry used during testing

measured 10.5 ft (3.2 m) wide by 7.3 ft (2.2 m) high and 944 ft

(287.7 m) long.

3.1.1. Experimental layout

A force plate (ACCUGAIT, Advanced Mechanical Technology, Inc.,

Watertown, MA) was embedded into the floor flush with the

walking surface of the mine at the end of a mine entry as seen in

Fig. 1.

Fig. 1. The test layout within the Safety Research Coal Mine. The curtain was lowered and raised for the near-field and far-field visual reference scenarios, respectively.

From the force plate, an un-obstructed view of 944 ft

(287.7 m) could be seen down the entry. All mine light sources were

turned off during testing with the only light source coming from

the cap lamp being tested. Typical mining machinery sounds were
played during testing to further simulate the mining environment.

A canvas curtain was used to simulate close field of view and was

hung at a distance of 14.4 ft (4.4 m) from the force plate across the

entry.

3.2. Cap lamps

Three LED cap lamps were used. Fig. 2 depicts these cap lamps

on a single mounting plate that is used for laboratory measurement

purposes.

Fig. 2. Cap lamps 3, 2, and 1 (left to right) mounted on a bracket used for laboratory

measurements.

During the testing, a single cap lamp was mounted to the

hard hat worn by the subjects. Each cap lamp was new, powered at

levels for a fully charged battery, and each had a cord that

connected to a power source located behind the subject. The cap

lamps’ electrical and photometric data are listed in Table 1.

Table 1

Cap lamp electrical and photometric data.

Cap lamp

(nm)

Electrical characteristics Photometric characteristics

Supply

voltage

(Vdc)

Supply

current

(ma)

Supply

power

(watts)

Peak

wavelength

Correlated

color

temp. (K)

1 4.00 760 3.04 452 8039

2 3.95 530 2.09 456 6603

3 2.96 450 1.33 448 6356

Cap

lamps 1 and 2 used a single phosphor-white LED as the primary

light source, along with an optical reflector to direct the light to

a circular spot beam ranging from about 6 to 8°. Fig. 3 depicts the

lighting distributions of two cap lamps. The lighting distribution

from cap lamp 2 is very similar to cap lamp 1, except that the

circular spot beam is directed an additional 4° downward to the

floor area. Both were approved by the Mine Safety and Health

Administration (MSHA). Cap lamp 3 was a laboratory prototype

developed by NIOSH to improve the ability of miners to see mining

hazards. This prototype uses multiple, phosphor-white LEDs as the

primary light source along with secondary optics to better

illuminate specific hazardous areas in the mine. The mine’s walls

are within the subject’s field of view; thus they serve as a vertical

frame of reference. The more the walls are illuminated, the more

visible they become. The left and right wall illuminance was

measured at a distance of 10 ft (3 m) ahead of the subject. For each

wall, an illuminance measurement was taken at 2-ft (0.6-m)

intervals starting at the floor and stopping near the mine ceiling.

Fig. 4 depicts the vertical illuminance distribution for the left and

right walls.

3.3. Procedure

During data collection, subjects were given standard mining

personal protective equipment (hard hat, clear-framed safety

glasses, a miner’s belt with a cap lamp battery, self-contained selfrescuer, and steel-toed safety boots) and asked to enter the SRCM.

Safety boots were standardized across subjects, with all subjects

wearing the same make and model boots. The subjects were given

time (about 15 min) to acclimate to the dark conditions of the mine

before data collection begun. During each test, the subject was

asked to stand quietly on the force plate with their eyes facing

forward (down the entry). The subject’s feet placement was standardized by a guide which allowed for 2-in (5-cm) inter-foot

spacing (see Fig. 5). The subject then donned the appropriate cap

lamp based on the randomization scheme. A series of seven trials of

quiet standing (each for 60 s collected at 100 Hz) with eyes open

was collected using the Balance Clinic software (Advanced

Mechanical Technology, Inc., Watertown, MA). This was repeated

using each of three cap lamps and the two visual reference

scenarios (near-field and far-field), for a total of 42 trials. A customwritten software script (MATLAB®; The MathWorks, Inc, Natick,

MA) was used to calculate CPVML, CPVAP, RMSML, RMSAP, and SA.

4. Results

The ANOVAs comparing the three cap lamps and two visual

reference conditions across age categories only yielded significant

differences for the effect of visual reference on RMSAP. Cap lamp

condition approached significance (p < 0.077) for CPVML. The

means of the dependent measures, collapsed across age categories

and by visual reference and lighting condition, are given in Table 2,

and standard deviations are listed in parentheses.

The ANOVAs comparing the lighting conditions (baseline

condition and the near visual reference for three cap lamps)

indicated that lighting condition significantly affected CPVAP

(p < 0.0126), RMSML (p < 0.0046), and sway area (p < 0.023). The

results of the post hoc Tukey tests are shown in Table 2. Age category bordered on significant for RMSAP (p < 0.0503); however, the

data in Table 3 do not indicate that age was a significant factor.

The correlations between subject age and the dependent

measures for the baseline indicated a significant correlation

between age and CPVAP (r 1⁄4 0.40, p < 0.0275). The other correlations were not significant, with the correlation between age and

RMSAP (r 1⁄4 0.35, p < 0.0614) approaching significance.

5. Discussion

Overall, the results of this pilot investigation of the role of cap

lamp design on postural stability suggest that postural stability may

be significantly reduced when wearing a cap lamp in a mining

environment compared to a baseline lighted laboratory condition;

however, the cap lamp differences studied do not significantly

affect measures of static postural stability for the visual

environment of the SRCM. The results have several implications for

choosing cap lamps for underground use as well as for future

studies, as detailed below.

5.1. Cap lamps

While the results of this study do not indicate a statistically

significant difference among the cap lamps, prior NIOSH research

has implied that cap lamp 3 enabled the best visual performance

among LED cap lamps by comparison to cap lamps 1 and 2 as used

in the current research. Human subject test results indicate that cap

lamp 3 improved the ability to perceive moving objects in the

peripheral visual field by as much as 79.5%, with a 194.1% detection

time improvement for floor trip objects (Reyes et al., 2011) without
increasing discomfort glare (Sammarco et al., 2011). Thus, it

appears that with respect to safety, cap lamp 3 would enable

distinct advantages in visual performance and discomfort glare

without reducing postural stability when compared to the other

cap lamps.

Fig. 3. The light distributions from cap lamps a) 1 and b) 3.

Fig. 4. Vertical illuminance at a distance of 10 ft (3 m) ahead of the subject at: a) the left wall; b) right wall.

Fig. 5. Force plate showing placement of the feet and T-shaped separator.

5.2. Subject age

Volunteers utilized in this testing represented a wide range of

ages. Although age was not a significant factor in the analyses

carried out, the data in Table 3 suggest that there were trends, albeit

non-significant, in the outcome measures RMSP and sway area,

particularly for the oldest age group.

In accordance with the literature, baseline balance measures of

this study population also imply a detriment in balance functioning

with age where CPVAP (r 1⁄4 0.40, p < 0.0275 was significant and

RMSAP (r 1⁄4 0.35, p < 0.0614) approached significance.

This study was a pilot investigation into the effect of age and cap

lamp lighting distribution on postural stability; hence, only ten

subjects participated in each of the three age groups. These small

sample sizes increase the probability that the results could have

occurred by random chance. Also, the likelihood of inadvertently

increasing confounding factors increases because small groups are

likely to be less diverse than large groups. Increasing the sample

size in a larger study has the potential to yield significant results

with respect to age as a factor.

5.3. Limitations

Testing was conducted in the SRCM. In the test area, the mine

width was about 10.5 ft (3.2 m) as depicted by Fig. 1. This is about

half the width of entries commonly encountered in contemporary

room-and-pillar coal mines in the U.S., where the width is typically

about 20 ft (6.1 m). The SRCM dates back to 1910, when the

majority of the mining was conducted by older mining techniques

that used drills, cutting bars, and explosives to mine the coal.

Today, room-and-pillar coal mines use continuous mining

machines that can cut coal in widths ranging from approximately

16 ft (4.9 m) to 22 ft (6.7 m). In these conditions, the mine wall

illumination depends on the distance from the light source to the

mine wall, where the illumination varies according to the inverse

square law. Thus the wall illumination in a typical room-and-pillar

coal mine would decrease by a factor of four given a mine width of

21 ft (6.4 m). This would reduce the illumination below that

provided, for instance, by a full moon on a clear night. It is

unknown if this reduced illumination would negatively affect the

usefulness of the wall as a visual frame of reference. However,

previous research has found that restricting peripheral vision
(through wearing personal protective eyewear) is likely to affect

balance negatively, and this may be comparable to walking in an

area with dimly illuminated walls (Wade et al., 2004). Additional

research is needed to address this potential issue.

Standing and walking are considerably different activities.

However, while most falls occur during walking, the risk for

falling is often determined via static standing measurements of

postural stability. In the case of the current study, it was

impractical to attempt dynamic measures due to the difficulty of

equipping the mine and maintaining consistent walkway conditions. In general, loss of balance is commonly a triggering event

for a fall accident, and postural stability measures obtained during

static standing correlate well with risks for falls (Duncan et al.,

1992; Simeonov and Hsiao, 2001; Topper et al., 1993).

The foot placement guide discussed in the procedure was not

removed prior to testing, however the force plate was zeroed out

with the guide placed on the force plate before the subject stepped

onto the force plate. The effect of the guide remaining on the force

plate was measured during pilot testing and it was found that the

guide did not significantly affect the measurements taken, however

it could have prevented the detection of very slight significant

differences in the data.

Locomotion in an underground coal mine is substantially

different than in many other occupational environments. Not only

is there poor lighting, but miners must also wear protective

eyewear and footwear in addition to other tools and safety devices

attached to their belts. These protective measures may reduce

peripheral vision and affect the dynamic stability of miners when

walking in an underground coal mine, where they are constantly

navigating the uneven mine floor terrain. Although the authors

believe that the balance effects noted in this study will correlate to

those experienced during walking (since all subjects wore typical

mining PPE), the additional hazard recognition required during

walking in a mine is a concern. Additional research would be

needed to address this potential issue.

Although only LED cap lamps were studied, there are still many

incandescent cap lamps in use. It is possible that including incandescent cap lamps may have resulted in greater differences within

cap lamps, especially given the research mentioned previously

indicating superior performance of LED over incandescent cap

lamps with respect to visual performance. The results did suggest

that postural stability appears to be negatively influenced by

underground lighting conditions, and these differences are likely

contributors to the problem of slips and falls in underground mines.

Lastly, remote control and automation is being increasingly

deployed in coal mining for a number of reasons such as to remove

operators from hazardous situations, improve productivity, lessen

environmental impact and to mine areas that were previously

inaccessible (Hoberry et al., 2011). The scope of this pilot study did

not include such remotely-controlled or automated mining equipment. The illumination environment improves when remote

control and automation is not used because mining equipment is in

close proximity. The machine mounted lighting then helps to

increase the overall illumination thus providing miners with better

illumination of visual cues, hazards, and visual frames of references.

Remote control and automation results in a higher dependence on

the cap lamp because the equipment illumination is farther away

and contributes less to illuminating the mine environment by the

inverse of the square of the distance to the miners.

Table 2

Means (standard deviations) of postural sway by visual reference and lighting (3 camp lamps, baseline laboratory) conditions.

Dependent measure

CPVML (mm/sec) CPVAP (mm/sec) RMSML (mm) RMSAP (mm) Sway area (mm2

)

Visual reference Visual reference Visual reference Visual reference Visual reference

Lighting Near Far Near Far Near Far Near Far Near Far

Baseline (Lab)

Cap lamp 1

Cap lamp 2

Cap lamp 3

0.22 (0.03)

0.23 (0.04)

0.23 (0.04)

0.23 (0.05)

e

0.22 (0.03)

0.23 (0.04)

0.23 (0.04)

b

0.32 (0.04) a,b0.35 (0.07) a

0.35 (0.06) a

0.35 (0.05)

e

0.35 (0.05)

0.37 (0.09)

0.37 (0.09)

b

0.10 (0.04) a

0.12 (0.04) a

0.12 (0.04) a

0.12 (0.04)

e

0.11 (0.04)

0.12 (0.05)

0.12 (0.05)

0.17 (0.07)

0.19 (0.07)

0.17 (0.06)

0.17 (0.05)

e

0.16 (0.05)

0.16 (0.05)

0.16 (0.05)

b

0.31 (0.21) a

0.43 (0.36) a,b0.40 (0.25) a,b0.38 (0.25)

e

0.35 (0.21)

0.42 (0.42)

0.42 (0.42)

a,b Means with the same letter are not significantly different.

Table 3

Means (standard deviations) of dependent measures by age categories collapsed

across visual reference and lighting conditions.

Age group Dependent measure

CPVML

(mm/sec)

CPVAP

(mm/sec)

RMSML

(mm)

RMSAP

(mm)

Sway area

(mm2

)

18e25 0.23 (0.03) 0.33 (0.06) 0.11 (0.03) 0.16 (0.04) 0.34 (0.16)

40e50 0.22 (0.04) 0.35 (0.06) 0.10 (0.05) 0.15 (0.05) 0.32 (0.32)

51þ 0.23 (0.04) 0.36 (0.07) 0.12 (0.04) 0.20 (0.07) 0.49 (0.33)

6. Conclusions

The aim of this research was to provide initial quantification of

the effects of improved lighting on postural stability which can be

a contributing factor for STF accidents in underground mining.

Vision plays a large role in preventing STF accidents and serves two

purposes: 1 e it exposes the presence of objects allowing them to

be evaded and 2 e it reveals changes in the environment that

necessitate a change in locomotive action (Howarth, 2006).

Previous research conducted by NIOSH has demonstrated the

ability of LED-based cap lamps to improve hazard detection. Results

of this study did not find a significant difference in postural stability

between different designs of LED-based cap lamps, but did show

a significant decline in postural stability when moving from a fully

lit laboratory to an underground coal mine. Future studies, such as

those by Reyes et al. (2011, in press), will be necessary to determine

the gain in other performance measures for reducing STF accidents

realized with improved cap lamp technology.

Acknowledgments

The studies described in this paper were conducted with

assistance from J. Carr, A. Cook, T. Matty, M. McElhinney, M. Nelson,

M. Reyes, J. Sable, J. Srednicki, and the research volunteers. Vision

testing was conducted by M. A. Rossi, R.N. All those cited above

were employees of NIOSH at Bruceton, PA.

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