Helmet-Mounted Displays: - USAARL - The - U.S. Army

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Optical Performance 117 Figure 5.5. Typical catadioptric HMD optical design. images. Nominal values for the transmittances and reflectances of the various optical media are: 70% canopy transmittance; 85% and 18% transmittance for a clear and shaded visor, respectively; 70% transmittance (ambient towards the eye); 70% reflectance (CRT luminance back towards the eye) for the spherical combiner, 60% transmittance (ambient towards the eye) and 40% reflectance (CRT luminance) for the plano combiner. An analysis of this design shows that approximately 17% of the luminance from the CRT image (and CRT optics) and approximately 25% of the ambient scene luminance reaches the eye for the clear visor (5% for the shaded visor). Ambient scene luminances vary greatly over a 24-hour period. They can range from 0.001 fL under moonless, clear starlight conditions to 10,000 fL for bright daylight. Daytime luminances begin at approximately 300 fL. The image source used in Figure 5.5 is a miniature CRT. Depending on viewing time, day versus night, luminance values provided by the CRT and its associated optics can be selectively ranged from 100 fL (for night use) to an optimistic 1600 fL (for day use). A luminance of 800 fL may be a more typical daytime value. Image contrast during night operations is usually not a problem. However, the use of HMDs for daytime imagery (versus for symbology) is not well defined. Based on the design in Figure 5.5 and the nominal
118 Clarence E. Rash and William E. McLean values provided, Table 5.4 provides the theoretical values for Michelson contrast (C m, Eq. 5.3a and 5.3b), contrast ratio (C r , Eq. 5.2a), and shades Table 5.4. Michelson contrast, contrast ratio, and SOG values for an HMD design. Display luminance 100 fL 400 fL 800 fL 1600 fL Clear visor C m = 0.01 C r = 1.02 SOG=1.06 C m = 0.04 C r = 1.09 SOG=1.25 C m= 0.08 C r = 1.18 SOG=1.48 C m= 0.15 C r = 1.36 SOG=1.89 Ambient luminance 3,000 fL 1,000 fL 300 fL Shaded visor C m= 0.05 C r = 1.11 SOG=1.29 C m= 0.17 C r = 1.42 SOG=2.02 C m= 0.30 C r = 1.85 SOG=2.77 C m= 0.46 C r = 2.69 SOG=3.87 Clear visor C m= 0.03 C r = 1.07 SOG=1.19 C m= 0.12 C r = 1.27 SOG=1.69 C m= 0.21 C r = 1.54 SOG=2.25 C m= 0.35 C r = 2.08 SOG=3.11 Shaded visor C m= 0.14 C r = 1.32 SOG=1.80 C m= 0.39 C r = 2.27 SOG=3.37 C m= 0.56 C r = 3.54 SOG=4.66 C m= 0.72 C r = 6.07 SOG=6.22 Clear visor C m= 0.10 C r = 1.22 SOG=1.59 C m= 0.32 C r = 1.90 SOG=2.85 C m= 0.47 C r = 2.79 SOG=3.97 C m= 0.64 C r = 4.58 SOG=5.40 Shaded visor C m= 0.35 C r = 2.06 SOG=3.09 C m= 0.68 C r = 5.23 SOG=5.79 C m= 0.81 C r = 9.45 SOG=7.50 C m = 0.89 C r =17.91 SOG=9.35 of grey (SOG, Eq. 5.9) for various combinations of visors, ambient scene luminances, and CRT display luminances. In these equations, the ambient luminance reaching the eye assumes the role of the background luminance and the sum of the CRT and background luminances reaching the eye assumes the role of the target luminance. Note that for the purpose of these calculations, the background luminance is a combination of the light reaching the eye due to both the ambient and the CRT luminances. See Appendix for a sample calculation of Michelson contrast, contrast ratio, and shades of grey values for the set of conditions for viewing an 800 fL CRT against a 3,000 fL ambient scene using both clear and shaded visors. Several obvious trends are present in the data of Table 5.4. These are: (a) for a given ambient background luminance, increasing the CRT display luminance increases contrast; (b) for a given CRT display luminance, increasing ambient background luminance decreases contrast; and (c) for a given set of CRT display and ambient background luminances, the use of a shaded visor over a clear visor increases contrast. Contrast requirements. Once appropriate figures of merit have been established for quantifying contrast, an obvious question is what are their recommended values. Unfortunately, there is no single value or set of
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Helmet-Mounted Displays: Design Iss
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The views, opinions, and/or finding
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vi Contents 4. Visual Coupling Clar
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viii Contents References ..........
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x Ben T. Mozo, Research Physicist U
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xii Foreword began its phenomenal e
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xiv Preface Acknowledgments The aut
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Introductory Overview 1 Clarence E.
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Introductory Overview 5 Figure 1.2.
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Introductory Overview 7 The trend f
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Introductory Overview 9
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Introductory Overview 11 aviator to
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Introductory Overview 13 1970's. Ta
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Introductory Overview 15 Image sour
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Introductory Overview 17
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Table 1.3. HMD performance figures-
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Introductory Overview 21 direct vie
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Introductory Overview 23 Figure 1.9
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Introductory Overview 25 Figure 1.1
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Introductory Overview 27 Ercoline,
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Introductory Overview 29 II, Procee
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Introductory Overview 31 Armstrong
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34 Clarence E. Rash, Melissa H. Led
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40 Liquid crystal Clarence E. Rash,
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Optical Designs 3 William E. McLean
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Optical Designs 57 and plotted in l
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Optical Designs 59 phosphors, (b) u
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Optical Designs 61 optics. Examples
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Optical Designs 63
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prism combiner. Optical Designs 65
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Figure 3.2. (continued) Optical Des
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Page 116: DESIGN ISSUES PART TWO
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Page 121 and 122: 104 Contrast Clarence E. Rash and W
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168 Number of SOG = � log (C r) /
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Visual Performance 6 William E. McL
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Visual Performance 171 observer is
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seen. Visual Performance 173 Figure
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Visual Performance 175 perception.
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Visual Performance 177 with monovis
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Visual Performance 179 individuals
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Visual Performance 181 0 to -5.25 d
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Visual Performance 183 Report No. 9
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Biodynamics 7 B. Joseph McEntire He
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Biodynamics 187 behavior of this de
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Figure 7.2. Head anatomical coordin
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Biodynamics 191
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Biodynamics 193 al., 1972), and man
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Biodynamics 195 Figure 7.5. Vertica
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Biodynamics 197 disability and fata
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Biodynamics 199 been fabricated int
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Biodynamics 201 Ty pic al acc ele r
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Biodynamics 203 exceed the mechanic
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Biodynamics 205 complexity and comp
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Type Reference helmet Foam in place
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Biodynamics 209 the fitting problem
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Biodynamics 211 adjustment buckle,
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Biodynamics 213 down. The helmet ma
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Biodynamics 215 Desert Shield/Deser
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Biodynamics 217 Donelson, S. M., an
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219 Fort Rucker, AL: U.S. Army Aero
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220 Ben T. Mozo Figure 8.1. Noise l
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222 Ben T. Mozo available in the ne
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224 Ben T. Mozo Protectors”(ANSI,
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226 Ben T. Mozo language. Tests of
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228 Ben T. Mozo Figure 8.6. Speech
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230 Ben T. Mozo the communications
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232 Ben T. Mozo Item Mass (grams) C
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Ribera, J. E., and Mozo, B. T. Unda
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236 Joseph R. Licina operational us
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238 Joseph R. Licina Standard MIL-S
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240 Joseph R. Licina On electro-opt
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242 Joseph R. Licina For HMDs with
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244 Joseph R. Licina 1994b) that wi
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246 Joseph R. Licina Table 9.2. Hea
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248 Joseph R. Licina provided a 93.
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250 Joseph R. Licina and buckles, a
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252 Joseph R. Licina authorized to
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254 Joseph R. Licina a nuclear flas
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256 Joseph R. Licina requirements:
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HMD PERFORMANCE ASSESSMENT PART THR
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262 Clarence E. Rash, John C. Mora,
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Glossary 11
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270 making stereoposis possible. Bi
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272 John C. Mora and M elissa H. Le
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NOTES ON CONTRIBUTORS Melissa H. Le
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Notes on Contributors 281 Research
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284 Index Breakaway force (see Fran
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286 Index movement, 55, 80, 84, 90,
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288 Index 198, 204, 205, 208, 210,
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290 Index Microphone, 15, 186, 224,
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292 Index Speech intelligibility (S
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