This is a compilation of various material I find useful for understanding the theoretical foundations of a flashlight’s function. Some of these pages are not on the mainstream radar and difficult to search for, hence this post.
Being a somewhat self-centered individual, many of these are within my scope of interest/knowledge (or even my own threads); this unfortunately means the exclusion of many excellent pages on topics I know little about (e.g., drivers and circuits). On the bright side, it also means that I can personally vouch for the accuracy/utility of items on this page.
Hope the broader community also finds this page helpful, either as a quick reference or a gateway to doing flashlight theory research yourself. Feel free to suggest more pages you find helpful!
Citable data sources
- Comprehensive library of well-controlled flashlight reviews, with extreme throwers measured using proper methodology. 1Lumen LED flashlight reviews: THE source on the internet for Flashlight Reviews
- Fantastic collection of well-controlled beamshots and tests of different configurations of the same light: Flashlight comparator - Grzybek Reviews
- A library of detailed LED performance tests: koef3's LED Tests
- Another library of detailed LED performance tests, mostly of older and unusual emitters: djozz tests
- A visual map of flashlights based on output and throw, great for quick comparisons: The Map of Flashlights - put your light on the Map!
Beam profile and general optical design
- A calculator for the collection efficiency of reflectors and lenses: Calculator for reflector/lens collection efficiency; hotspot/corona breakdown
- An illustrated clarification of the terms “hotspot, corona, spill”, plus rough estimation formulas: Definitions and Formulas of a forward-reflector beam profile
- An extremely comprehensive physics-engine simulator for reflector beams: I built a Flashlight Beam Simulator. Free for anyone to use.
- A reflector beam profile calculator. Less comprehensive than the simulator but simpler/faster, accuracy validated by the simulator: Calculator for reflector beam profile
- A similar beam calculator, verified accurate for lenses and recoil reflectors but not standard/forward reflectors: Advanced calculators for theoretical lumens, lux, beam divergence, and more, of custom LED flashlights
- An easy-to-use ray-tracing tool (Phydemo) for simulating all sorts of reflectors and lenses.
- An extremely comprehensive/advanced optical design tool–thank you @Enderman for the suggestion!
- A set of very clear expository slides on optical elements in a flashlight.
Theoretical results relating to throwers
- A simple ballpark throw estimate for any light: Simple formula for thrower estimation: ANSI m ≈ 24*(optic diameter in mm)
- Throw calculator given LED+reflector parameters: Calculator for reflector beam profile
- A quantitative answer to a common question: how do a reflector’s depth and diameter affect throw? Depth & diameter vs intensity in a forward reflector
- A formula relating candela, lumens, and beam angle in a uniform beam: Relation between candela, output, and beam angle
- Real-world throw calculator that accounts for atmospheric scattering, which becomes significant at 1km+ distances: Calculator for usable throw
- A basic expository article (translated from TLF) on what features of a reflector/optic affects throw: Explanation of how secondary optic affects beam/throw (translated from TLF)
Colorimetry and spectrophotometry
- An incredibly comprehensive tool for digitizing a spectrum from an image file and generating a color report: Tool for digitizing an LED spectrum from an image
- A dedicated spectrum analyzer with a repository of user-submitted spectra: https://hcri.io
- A library of detailed LED performance tests: koef3's LED Tests
- Another great source for color measurements of mainstream lights: https://zeroair.org
- Attempted digest of a paper proposing a new geometric model for color space, which contains more differential geometry than I can digest: Quick digest of "The Geometry of Color in the Light of a Non-Riemannian Space"
Experimental work
- Adding a dome to a flat LED to adjust CCT and tint: Doming a flat LED to adjust CCT and tint
- A simpler, more precise alternative to “integrating shoebox” for measuring total output: A simpler, more reliable alternative to the integrating shoebox
- An analog battery indicator using the correspondence between Vf and color: Convoy tailcap mod with moonlight and analog battery indicator
Tools/applications pending peer review
- A ray-tracer/optical design tool: Etendue Bench
- A spectrum mixer/analyzer: LED Spectrum Lab
- Driver for X-Rite i-1 spectrometer: GitHub - git67-67/i1pro-webusb: driver for i1pro · GitHub
- Simulator of how Lee color filters interact with various LEDs: GitHub - git67-67/gel-chromaticity-map · GitHub
