I built a free flashlight calculator suite – 14 tools for candela, throw, lux, lumens, runtime & more

Commercial Sellers' Spot
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Hi everyone,

I’m Ivan from Kiroff Flashlights in Bulgaria. I’m a commercial seller, so I’ll keep this thread here in the Commercial Sellers’ Spot.

I’ve been working on something for a while that I think some of you might find useful.

I built a free flashlight calculator suite with 14 different calculators covering:

• Candela → ANSI beam distance
• Beam distance → required candela
• Candela → lux at a given distance
• Lux → candela
• Lumens → candela by beam angle
• Candela → lumens by beam angle
• Battery mAh → Wh
• Theoretical runtime
• Efficiency (lm/W)
• Flashlight comparison by candela
• Throw comparison
• Lux comparison at a given distance
• Color temperature / Kelvin
• Meters ↔ feet

The idea wasn’t to make another generic “online calculator”.

I wanted to put the calculations that flashlight people actually use in one place, show the formulas/methodology behind them, and make the individual calculators easy to link to.

There are also direct links to each calculator, copy citation, copy result, shareable pre-filled URLs, and an option to embed individual calculators on another website.

https://fener-bg.com/page/flashlight-calculators

For example, this URL can open the Candela → Lux calculator with the values already entered and the result calculated:

https://fener-bg.com/page/flashlight-calculators?calc=candela-to-lux&cd=250000&m=100#candela-to-lux

I also made an English version specifically because I wanted the tools to be useful outside Bulgaria as well.

Since BLF has a lot of people here who understand this stuff much better than the average flashlight user, I’d actually appreciate some criticism.

If you spot a formula that is wrong, an assumption that isn’t valid, something that should be explained differently, or simply a calculator that would be useful and is missing — please let me know.

I’m much more interested in making the tools technically useful than in making them look impressive.

And yes, the project is on my own flashlight website, but the calculators are completely free and don’t require registration or anything else.

I’d be genuinely interested to hear what you guys think.

2 Thanks
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Great to hear about this project! As a fellow developer for various flashlight-related calculators, I’m very excited to see this.

So far most of the calculators look great, I just have 2 comments.

  1. About beam angle: I looked at the formulas underlying the calculator, and notice that they assume that the beam is round and perfectly uniform in intensity. This is evidently not the case for most types of optics, which produce an intensity gradient (hotspot, corona, spill, etc.).

For this reason, the beam angle calculator is not applicable to all but one type of light: one with a convex/Fresnel lens paired with a round LED, whose projected beam does satisfy the assumption of being round and uniform. I think it is important to state this caveat in the calculator, because otherwise it is unclear what “beam angle” even means.

For a reflector or TIR light not satisfying the above assumptions, the “beam angle” from the calculator does not represent any part of the actual beam–it serves as a lower bound for spill angle and an upper bound for hotspot angle, but is otherwise difficult to interpret.

If you’re interested in actually computing the hotspot/corona/spill angles of a reflector light, that opens up a huge can of worms. I spent a couple of weeks pinning down the relevant definitions and chugging through the trigonometry to produce a calculator given suitable parameters like LED and reflector dimensions. Fellow community member @Probably developed a physics engine to numerically simulate a reflector beam and measure these quantities after simulation; this ended up being a much more advanced/complex project.

  1. The measure lm/W is called (luminous) efficacy, not efficiency. Efficiency is always a unitless proportion/percentage.