This is a list of skies available in the Steam caches, along with pictures of each skybox. The light_environment settings listed (Ideal Sun Angle, Ideal Brightness, etc) are suggestions based on settings used in official maps; other values may also be appropriate. To test skies in singleplayer without recompiling the map, bring up the console and enter sv_skyname <sky_name>. Quicksave the game, load it again and the old skybox should be temporarily replaced with the new one.
source materials.gcf
These skyboxes are available to Half-Life 2 and all games and mods using the Source Engine. 
The table below explains the prefixes used in map filenames.
Only outdoor maps that have both skyboxes and light_environments are referenced by this list.
| Sky Name & Picture
 | Example Map
 | Ideal Sun
 Angle
 | Ideal Sun
 Pitch
 | Ideal Brightness
 | Ideal Ambience
 | 
| sky_borealis01 
  | None | 0 47 0 | -45 | 254 227 167 80 | 195 195 195 20 | 
| sky_day01_01 
  | d1_trainstation01 - d1_trainstation_06 | 0 165 0 | -35 | 237 218 143 800 | 190 201 220 100 | 
| sky_day01_04 
  | d1_canals_01, d1_canals_01a, d1_canals_02 | 0 165 0 | -55 | 248 234 205 1000 | 194 236 252 175 | 
| sky_day01_05 
  | d1_canals_03 d1_canals_05
 d1_canals_06, d1_canals_07
 d1_canals_08
 de_prodigy
 | 0 165 0 0 104 0
 0 104 0
 0 104 0
 0 316 0
 | -83 -35
 -35
 -35
 -70
 | 243 224 158 1200 248 233 186 800
 248 233 186 860
 243 219 143 860
 249 227 155 800
 | 194 236 252 225 140 167 174 150
 140 167 174 150
 140 167 174 150
 126 171 207 1000
 | 
| sky_day01_06 
  | d1_canals_09, d1_canals_10, d1_canals_11 cs_compound
 | 0 148 0 0 104 0
 | -35 -35
 | 240 187 117 1000 248 233 186 860
 | 135 172 180 150 140 167 174 150
 | 
| sky_day01_07 
  | d1_canals_12 | 0 108 0 | -35 | 235 166 71 1000 | 135 172 180 150 | 
| sky_day01_08 
  | d1_canals_13, d1_eli_01 | 0 108 0 | -35 | 235 155 71 1000 | 105 142 165 120 | 
| sky_day01_09 
  | d1_eli_02 d1_town_01 - d1_town_03
 | 0 12 0 0 12 0
 | -45 -45
 | 175 230 239 65 175 230 239 50
 | 83 104 130 50 43 45 57 5
 | 
| sky_day02_01 
  | d1_town_05 | 0 225 0 | -25 | 254 242 160 400 | 172 196 204 80 | 
| sky_day02_02 
  | d2_coast_01 de_port
 | 0 225 0 0 230 0
 | -20 -20
 | 255 244 213 700 255 244 213 700
 | 172 196 204 50 172 196 204 50
 | 
| sky_day02_03 
  | d2_coast_03 d2_coast_04
 | 0 280 0 0 290 0
 | -45 -45
 | 243 238 224 500 243 238 224 500
 | 172 196 204 100 172 196 204 50
 | 
| sky_day02_04 
  | d2_coast_05 | 0 240 0 | -45 | 243 238 224 400 | 172 196 204 50 | 
| sky_day02_05 
  | d2_coast_08 | 0 135 0 | -30 | 255 255 249 448 | 172 196 204 100 | 
| sky_day02_06 
  | d2_coast_09 | 0 270 0 | -20 | 255 252 230 475 | 172 196 204 120 | 
| sky_day02_07 
  | d2_coast_10 d2_coast_11
 | 0 225 0 0 225 0
 | -15 -15
 | 255 252 230 500 255 0 0 400
 | 183 204 210 140 175 199 205 150
 | 
| sky_day02_09 
  | d2_coast_12 d2_prison_01
 d2_prison_02 - d2_prison_08
 | 0 200 0 0 200 0
 0 200 0
 | -5 -5
 -5
 | 237 232 209 70 217 226 234 0
 221 232 240 20
 | 122 140 169 60 122 140 169 20
 103 143 184 125
 | 
| sky_day02_10 
  | d2_coast_07 | 0 135 0 | -30 | 255 255 249 448 | 172 196 204 100 | 
| sky_day03_01 
  | d3_c17_01 d3_c17_02
 d3_c17_03
 | 0 165 0 0 126 0
 0 150 0
 | -35 -25
 -30
 | 237 218 143 800 245 200 150 1000
 236 218 145 600
 | 190 201 220 100 148 173 205 60
 160 184 211 150
 | 
| sky_day03_02 
  | d3_c17_04 d3_c17_05
 | 0 140 0 0 120 0
 | -35 -35
 | 236 218 145 650 236 218 145 650
 | 160 184 211 150 160 184 211 150
 | 
| sky_day03_03 
  | d3_c17_06a d3_c17_06b, d3_c17_07
 | 0 120 0 0 115 0
 | -40 -35
 | 236 218 145 700 236 218 145 700
 | 160 184 211 150 160 184 211 150
 | 
| sky_day03_04 
  | d3_c17_08 d3_c17_09
 d3_c17_10a, d3_c17_10b
 | 0 53 0 0 50 0
 0 50 0
 | -60 -35
 -20
 | 239 207 141 350 237 218 143 650
 238 207 142 600
 | 75 96 116 300 190 201 220 100
 190 201 220 100
 | 
| sky_day03_05 
  | d3_c17_11 d3_c17_12
 d3_c17_12b
 d3_c17_13, d3_citadel_01
 | 0 82 0 0 82 0
 0 40 0
 0 82 0
 | -12 -8
 -8
 -12
 | 238 200 128 450 238 200 128 450
 239 207 141 350
 238 200 128 450
 | 75 96 116 150 75 96 116 150
 75 96 116 300
 75 96 116 250
 | 
| sky_day03_06 
  | d3_breen_01, d3_citadel_05 | 0 280 0 | -21 | 221 112 13 300 | 255 255 255 20 | 
| sky_wasteland02 
  |  |  |  |  |  | 
 Note:The skybox material listed for d3_citadel_05 is sky_day03_06B.
Note:The skybox material listed for d3_citadel_05 is sky_day03_06B.counter-strike source shared.gcf
These skyboxes are available to Counter-Strike: Source and mods utilizing its content.
| Sky Name & Picture
 | Example Map
 | Ideal Sun
 Angle
 | Ideal Sun
 Pitch
 | Ideal Brightness
 | Ideal Ambience
 | 
| assault 
  | cs_assault |  |  |  |  | 
| cx 
  | de_chateau | 0 27 0 | -65 | 255 242 192 600 | 145 172 189 300 | 
| de_cobble 
  | de_cbble | 0 330 0 | -40 | 240 252 255 700 | 146 149 155 300 | 
| de_cobble_hdr 
  |  | 0 330 0 | -40 | 240 252 255 700 | 146 149 155 300 | 
| de_piranesi 
  | de_piranesi | 0 150 0 | -50 | 255 248 192 450 | 152 160 168 300 | 
| hav 
  | cs_havana | 0 300 0 | -12 | 251 215 140 800 | 143 176 214 300 | 
| italy 
  | cs_italy | 0 165 0 | -45 | 255 232 208 600 | 183 201 206 200 | 
| jungle 
  | de_aztec | 0 287 0 | -60 | 248 244 237 350 | 190 209 216 150 | 
| militia_hdr 
  | cs_militia |  |  |  |  | 
| office 
  | cs_office | 0 17 0 | -60 | 255 249 225 325 | 121 152 185 400 | 
| sky_dust 
  | de_dust, de_dust2 | 0 43 0 | -60 | 233 225 201 700 | 241 228 190 500 | 
| tides 
  | de_tides de_inferno
 | 0 51 0 0 307 0
 | -60 -65
 | 242 224 183 850 235 222 177 800
 | 105 150 186 800 91 135 149 400
 | 
| train 
  | de_train | 0 120 0 | -57 | 255 250 234 700 | 98 129 179 500 | 
| sky_c17_05 File:Sky c17 05.jpg
 |  |  |  |  |  | 
day of defeat source.gcf
These skyboxes are available to  and mods utilizing its content.
These skies are HDR capable.
 and mods utilizing its content.
These skies are HDR capable.
| Sky Name & Picture
 | Example Map
 | Ideal Sun Angle | Ideal Sun Pitch | Ideal Sun Scale
 | Ideal Sun Color
 | Ideal Light Angle
 | Ideal Light Pitch
 | Ideal Brightness
 | Ideal Ambience
 | (HDR) Ideal Brightness
 | (HDR) Ideal Ambience
 | 
| sky_dod_01_hdr 
  | dod_flash | 0 165 0 | -40 |  |  |  |  | 250 241 192 600 | 209 227 237 200 | 250 241 192 500 | 209 227 237 200 | 
| sky_dod_02_hdr 
  | dod_donner | 0 165 0 | -40 |  |  |  |  | 242 240 219 450 | 149 171 181 250 | 234 230 196 370 | 149 171 181 300 | 
| sky_dod_03_hdr 
  | dod_anzio | 0 32 0 | -50 |  |  |  |  | 250 241 192 600 | 209 227 237 200 | -1 -1 -1 1 | -1 -1 -1 1 | 
| sky_dod_04_hdr 
  | dod_avalanche | 0 60 0 | -50 |  |  |  |  | 250 241 192 600 | 149 171 181 250 | 250 241 192 425 | 149 171 181 200 | 
| sky_dod_06_hdr 
  | dod_argentan | 0 113 0 | -22 | 12 | 255 240 224 | 0 110 0 | -32 | 255 255 164 600 | 203 216 235 200 | 255 255 164 500 | 203 216 235 200 | 
| sky_dod_08_hdr 
  | dod_kalt | No sun | No sun | No sun | No sun | 0 45 0 | -44 | 197 205 214 750 | 136 175 204 280 | 197 205 214 750 | -1 -1 -1 1 | 
lostcoast content.gcf
These skyboxes are available to Half-Life 2: Lost Coast and mods utilizing its content.
These skies are HDR capable.
| Sky Name & Picture
 | Example Map
 | Ideal Sun
 Angle
 | Ideal Sun
 Pitch
 | Ideal Brightness
 | Ideal Ambience
 | (HDR) Ideal Brightness
 | (HDR) Ideal Ambience
 | 
| sky_lostcoast_hdr 
  | d2_lostcoast | 25 345 0 | -32 | 253 236 198 400 | 136 155 191 255 | -1 -1 -1 1 | -1 -1 -1 1 |