The Science of Sunrods

Sunrods kind of tick me off.  Sure, I’ve heard the arguments; basically, is “light” important in your game?  But 20 squares?  100 ft?  Really?  I started wondering, how many lumens is that?  The answer is, as science always is, complex.

I’m by no means a math or science wizard, if any of my research nets false results, feel free to let me know.  This is my first delve into all this.

The first thing I had to learn was the terminology.  I found a decent article that does a good job of putting this all into lamens terms.

  • A lumen is how bright a lit object is, one foot from the source of light.
  • A footcandle (U.S. term) is how bright the light is, one foot from the light.
  • A lux, or illuminance, is how bright the room gets because of the light.

Ok, we know a sunrod sheds “bright light out to twenty squares.”  So now, we have to define “bright light”.  This brings us into the science of the humans eyes reaction to light.

  • Photopic vision is how well the human eye can see in well-lit conditions.
  • Scotopic vision is how well the human eye can see in dim-light (darkness).
  • Mesopic vision is the combination of the two.

Further breakdown reveals that photopic vision “sees” in a cone like fashion at great detail and color perception; while scotopic vision “sees” wavelengths of light solely with the rods of our eyes yielding a severe loss of detail and color discrimination.  Mesopic is the combination of the two, it “sees” with both the cone and the rod,

This is all from wiki of course, I came across an interesting tidbit under scotopic vision, “In other species, such as the Elephant Hawk-moth (Deilephila elpenor), advanced color discrimination is displayed.”  In my opinion, this is clearly darkvision, proving that darkvison can see colors and allows us to do a perfect breakdown, into D&D terms.

  • Photopic = Bright Light – Detail and color
  • Mesopic = Dim Light – Loss of detail and color
  • Scotopic = Darkness – No detail, no color

Now, back to the sunrod.  We now know, in scientific terms, it produces photopic vision one hundred feet from it’s source, but there are varying degrees of photopic vision.

This is where I have to get into math, and like I said, not my strong suit.  Feel free to help me out here.

A flux of 1000 lumens, concentrated into an area of one square metre, lights up that square metre with an illuminance of 1000 lux. The same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.

metre = 3.2808399 ft

square meter = 10.763911 square feet

ten square meters = 107.6 ft (at ~ 100 lux).

One footcandle ≈ 10.764 lux.

So the twentieth square is (approximately) ten footcandles, and ten foot candles is equal to 107.6391 lux.

I found a nice relationship chart here

  • Full daylight is about 10,000 lux
  • A cloudy day is about 1000 lux
  • A lit parking lot at night is about 10 lux
  • A full moon is about 0.1 Lux.

This gives us something we can envision…. but remember that part from before, the same 1000 lumens, spread out over ten square metres, produces a dimmer illuminance of only 100 lux.

That’s a ratio of about 1 to 10.  We can easily work backwards from there to determine that the sunrod itself is 1000 footcandles (the same as an overcast day).

1000 footcandles = 10,763.91 lux (full daylight).  That’s bright!  Real bright!

What does that mean for the person holding a sunrod?  Can anyone see past them?  Can anyone even see them at all, or are they just a ball of brilliant light?  Not to mention the effect this would have on the scotopic eye.

Check this out.  It’s a tactical flashlight that produces 60 lumens, supposedly “enough to temporarily blind and disorient a person by impairing his night-adapted vision.”  Remember a lumen is how bright a lit object is, as opposed to how bright the light itself is (foot candle), but the two measurement are about the same, just two sides of the same coin.  So 60 footcandles is “enough to temporarily blind and disorient a person by impairing his night-adapted vision.”

What does 1000 foot candles do?

— Revision —

That’s it for now, I’m tired.

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About j0nny_5

Mid-thirties and work a full-time job in beautiful northern Colorado. In my free time I play D&D, video games, and walk my two beautiful Bouvier des Flandres.
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8 Responses to The Science of Sunrods

  1. Ben says:

    It’s hard to argue that a campfire produces “bright” illumination out to 50′ when I’ve had trouble reading a book by firelight at a mere 10′. On the other hand, I’ve gone walking in the woods at night and turned off my flashlight because the light from the stars was more than enough once my eyes adapted. There are other problems like phosphorescent fungi producing dim light out to 50′ without producing bright light anywhere, and if you assume that you can’t read by dim light, then it’s impossible to read by candlelight. This doesn’t even take into account that “bright” light spans the nearly million-fold difference in illumination between “Just bright enough to make out details” and “a painfully bright day”.

    By my calculations, if you treat 10 lux as “not dim enough to be dim light” and therefore “bright” light, then the sunrod is producing around 100,000 lumens, which is ridiculous, since a moderately bright lightbulb is ~1000 lumens. Even ignoring how painfully bright it is, it’s got to be disorienting to have an entire battlefield lit up by a single ultrabright light source being swung around on the end of a stick. Though by these calculations, a torch is around 7000 lumens, which is also insane.

    Personally I think it’s too bright in the actual game sense. Since most 4E powers are 10 squares or less, “I light a sunrod” essentially means “I ignore the illumination rules”. This makes it so that the GM has to pull out all sorts of weird shenanegans in order to actually have the players deal with light and shadow (like snuffing all their light sources, or making magical clouds of shadow).

    As the DMg points out: the DM is in control of the light level at all times. So if I want to have a combat in a brightly lit room, then it can just have windows, or torches in the walls, or balls of magical light suspended from the ceiling. If I want to have combat in the dark, with PC’s running scared between tiny pools of light and throwing torches around in a desparate attempt to light up the darkness, then I don’t want that challenge obviated by something that comes in a standard adventurer’s kit.

    As for your alternate sunrod, I find it really weird. On the one hand, you made it blind and daze because the default sunrod is so dang bright, but on the other, you made it a giant zone of diffuse magical light, so there’s not actually a single bright point source to blind people anymore? Either fix alone would probably be OK, but both at once actually makes LESS sense, I think. And since it blinds and dazes EVERYONE, it will either be completely ignored in favor of everburning torches or the players will hack them into extremely cheap flashbangs that they use to pull off massive alpha strikes. I really don’t think there’s a middle ground.

  2. Matt says:

    I think its best to either 1) outlaw them more or less (too unrealistic b/c science) or 2) call R20bright an aura and accept Rule0 (a wizard did it)
    no offense, and maybe you were looking for a new idea to fill out your blog, but combining too much reality and fantasy kinda ruins my disbelief. if its realistic, and we cant do it, that’s fine. if its magic, and it happens, that’s cool too. but magic 1000000lux = bright=science = bad combination.
    What you’re saying would make sense if sunrods were an alchemical item, and if you ruled them as such, I’d agree 100%. However, my understanding is that they’re a low-level enchantment, so I’m all for accepting aura-light.

    Still love your game

  3. Pingback: The Science of Sunrods (Part 2 – A New Sunrod) | Standard Action

  4. Pingback: 64 Things to do with an Adventurers Kit | Standard Action

  5. Payton says:

    You might want to look at how Pathfinder handles the Sunrod.—final/goods-and-services#TOC-Sunrod

    “This 1-foot-long, gold-tipped, iron rod glows brightly when struck as a standard action. It sheds normal light in a 30-foot radius and increases the light level by one step for an additional 30 feet beyond that area (darkness becomes dim light and dim light becomes normal light). A sunrod does not increase the light level in normal light or bright light. It glows for 6 hours, after which the gold tip is burned out and worthless.”

    “Can adding additional sunrods to an area of darkness increase the light level?

    No, sunrods can never increase the light level of an area of darkness because they are not magical sources of light. In such an area, it automatically defaults to the ambient natural light level, and then reduces it one step.”

  6. I forgot to mention that you can look over the Pathfinder Reference Document online for ideas.

    or the free PDF version of the Core Rule book.

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