Alternate Spectra

GURPS only has three ranges of vision: ultravision (less than 400 nm), normal vision (400-700 nm), and thermographic vision (roughly 8-15 µm), and the rules for ultravision bear very little resemblance to reality. This leaves out quite a lot of the spectrum, though much of it is only uncommonly used. These are alternate rules for extended visual range:

    • Enhanced Color Perception [2/level]

    • You have more than three types of color receptor. Gives +1 to perception rolls where the ability to distinguish colors would be valuable (this includes most vision rolls and possibly a few perception rolls that are normally not affected by keen eyes), and allows seeing color distinctions that humans cannot see. It may be possible for a human with tetrachromacy to qualify for one level.

    • Near UV Vision [1]

    • Near UV vision allows seeing light in the range shorter than blue light; in practice, this means the ability to see UV-A (315-400 nm), as most UV-B and essentially all UV-C is blocked by the ozone layer. Rules text for ultravision notwithstanding, near UV vision is fairly useless; it averages around 5% the brightness of visible light (depending on time of day), penetrates water poorly (about a tenth as well as green), and is scattered more by atmospheric haze than longer wavelengths, meaning it's often more of a nuisance than a benefit (TL 7 film is sensitive to UV, and cameras would use UV filters to cut haze). The practical benefit of near UV vision is that it lets you see and see by UV lights (which are of limited value for stealth, as they cause fluorescence in common materials), and it's a good excuse for enhanced color perception; if you do not take ECP, UV appears blue to you. It's possible for a human with an artificial cornea to have near UV vision; this is actually a 0 point feature, as it makes you more vulnerable to snowblindness and similar problems.

    • Near IR Vision [0/2]

    • Near IR vision allows seeing light in the range 0.75-1.4 µm range; it is commonly found in night vision gear. Unless you take ECP, it appears as red to you (it is also possible to see only in near IR; this is a 0 point feature). Near IR should be treated as a form of vision, not a form of infravision -- room temperature objects do not glow significantly (in absolute darkness, an object that's boiling hot might be very slightly visible) and you should mostly expect to see by reflected light from the sun or other light sources. Near IR vision allows using infrared flashlights, and it functions as one level of night vision if the primary light source is thermal (most natural sources, but not LEDs, fluorescence, bio-luminescence, or other cold light sources), or two levels if the primary light source is a candle or similar bright flame. Near IR penetrates water very poorly, and water vapor will be somewhat visible.

    • Short Wave IR Vision [-50% on IR vision, or +10% to a better form of IR vision]

    • SWIR vision allows seeing light in the 1.4-3.0 µm range. SWIR is treated as a form of IR vision, as room temperature objects do glow slightly (treat as a darkness penalty of -5 if not using a light source). If you are using a light source, it grants one level of night vision for thermal sources, three levels for a bright flame.

    • Medium Wave IR Vision [-20% on IR vision, or 1 if you also have a better form of IR vision]

    • MWIR is like SWIR, but covers light in the 3-6 µm range, and only gives a -2 penalty if you aren't using a light source (the range 6-8 µm is stopped by water vapor and is fairly useless in atmosphere).