cross-posted from: https://sopuli.xyz/post/48392158

I can’t decide between the SFT-25R and SFT-40 emitters. The price difference between them is negligible, and every online article seems to have differing opinions on which one has more throw, spill, etc.

Also, I am indecisive on the colour temperature. 5000K is daylight coloured apparently, while 6500K is cooler (blue tinted) and 3000K is warmer (yellow tinted, only available for SFT-40). I don’t like cooler lights, so I guess I will probably go with 5000K (unless 3000K isn’t super warm, then maybe that one?)

I am going with the Conway T6 as it’s compatible with regular AA batteries (like my IKEA Laddas), but as I understand, lights with built-in charging functions (e.g. Skilhunt EC150) usually don’t work with NiMH batteries, only Li-ion 14500 batteries.* I don’t think the Conway T6 has that, but I could be wrong. The T6 also cokes in a really unique purple colour!

*small edit: I meant that the charging bits don’t always work for NiMH batteries for most flashlights, the light itself would still work. The wording is a little unclear, sorry about that!

edit 2: I’m purchasing the T6 w/ the SFT-40 3000K emitter! Thanks everyone!

  • ZakMEnglish
    3·
    2 months ago

    There are three different ways to quantify brightness:

    • Lumens - total light produced
    • Candela - lumens per steradian (angle)
    • Lux - lumens per square meter, which is proportional to candela and distance

    The FL1 standard for advertising flashlight performance includes a beam distance metric, which is how far away the light can illuminate an object at 0.25 lux (comparable to moonlight with the moon full and sky clear) at the most intense point in its beam. This can be computed from candela.

    So more lumens with the same candela would mean a larger hotspot in the middle of the beam, a brighter spill on the outer beam, or both. In this particular case, the SFT40 will have a larger, dimmer hotspot than the SFT25R, and a brighter spill (more lumens, less candela). Here’s an exaggerated example with high lumens on the left and high candela on the right. Both lights here are far larger and more powerful than the T6. Note that while the spill angle (the outer edges of the beam) is wider with the first light in the example, it will be the same width for all LED options in the T6; the hotspot is what will change size.

    Is the difference in output noticeable enough to negate the higher CRI? In what circumstances would you want a higher CRI over output, and vice versa?

    Negate is the wrong term here. Imagine you have a dog who likes to bed down in fallen leaves at the edge of your property and you want to use your flashlight to find him. If he’s white and the leaves are brown, candela is the most useful attribute to maximize; as long as there’s enough light on the dog, you’ll spot him easily. If your dog is brown, then seeing color detail will matter and more light will not help if the color contrast is insufficient.

    I almost always pick CRI over lumens, and I think that’s usually the right choice for people with normal color vision. Candela is a different story because there are several cases in which the high-candela LED option doesn’t exist in high-CRI, and color information is less relevant to most things I’m trying to spot at extreme distances than it is to everyday use.

    • sbeak@sopuli.xyzOPEnglish
      1·
      2 months ago

      In this particular case, the SFT40 will have a larger, dimmer hotspot than the SFT25R, and a brighter spill (more lumens, less candela).

      Okay, I think that makes sense. So the SFT25R has a more concentrated beam (higher candela) while SFT40 has more lumens but over a larger angle and lower candela. I think I will go with SFT40 then?

      If he’s white and the leaves are brown, candela is the most useful attribute to maximize; as long as there’s enough light on the dog, you’ll spot him easily. If your dog is brown, then seeing color detail will matter and more light will not help if the color contrast is insufficient.

      Ahh, okay, I think that makes sense! So a high CRI light will make it easier to distinguish contrast between similar colours (e.g. brown on brown).

      So should I go with the 3000K light w/ the SFT-40 emitter then? I have normal colour vision and like warmer lights.

      • ZakMEnglish
        2·
        2 months ago

        3000K does look warm, which some people like and others don’t.

        How far away do you need to see clearly? The Nichia 519A in 5000K (daytime sunlight) or 4000K (afternoon sunlight) might be a good fit.

        • sbeak@sopuli.xyzOPEnglish
          1·
          2 months ago

          Enough to see the path clearly when the environment is dark. I like warm lights, and from your description, it’s not super orangey or anything, so I will go with the 3000K! Thanks for all the help!

          I can always return the flashlight if I find 3000K to be too warm :D

          • ZakMEnglish
            1·
            2 months ago

            I’m not sure Convoy takes returns for non-defects. Shipping between China and presumably-not-China for a sub-$20 item just isn’t worth it.

            Even if they do, Convoy is a small business, not Amazon.

            • sbeak@sopuli.xyzOPEnglish
              1·
              2 months ago

              Returns from a local retailer, I’m not buying directly from Convoy.