Definition
TLA is the umbrella term for visual artifacts produced by temporal modulation of a light source — covering directly-visible flicker, the stroboscopic effect on moving objects, and the phantom-array effect during eye saccades. The IES Technical Memorandum TM-39 quantifies and specifies measurement methods for all three.
Source overview
IES TM-39-25 (an ANSI / IES American National Standard) defines temporal light artifacts as the umbrella concept for visual responses to time-varying light: direct flicker (visible at low frequencies, addressed by PstLM and IEEE 1789), the stroboscopic effect on moving objects (addressed by SVM), and the phantom-array effect during eye saccades (addressed by PAVM). TM-39 specifies sampling rates, observation windows, and reporting requirements consistent with each metric.
The underlying standard is paywalled or otherwise not directly reproducible here. The text above is a plain-language summary written by Slick Engineering — not a verbatim quote. Authoritative source linked below.
Technical detail
Per IES TM-39-25 §11.1, measurement sampling rates should be 200,000 samples per second or higher to cover the full TLA frequency range. Camera-based instruments (FlickerSpec at 240 fps) cover the direct-flicker portion (≤ 90 Hz); photodiode-based instruments are required for SVM and PAVM.
Each TLA metric targets a different perceptual mechanism, not a different intensity. They are not redundant — a light source can be excellent on PstLM and terrible on SVM (e.g., a TRIAC-dimmed LED with significant high-frequency content), or vice versa.
EU Ecodesign 2019/2020 references the PstLM portion of TLA for SLR (Single Lighting Regulation) compliance; SVM is mentioned in supporting documents but with less prescriptive thresholds.
Where it appears
- FlickerSpec Used here
Covers the direct-flicker portion of TLA today (PstLM + IEEE 1789). The photodiode-attachment roadmap extends coverage into SVM and eventually PAVM bands.
Related terms
- PstLM
PstLM is a single-scalar perceptual metric for how annoying flicker from a light source is to a static human observer. PstLM = 1.0 correspon…
- SVM
SVM is a perceptual metric for the stroboscopic effect — the apparent stuttering or jagged motion of a moving object under modulated light. …
- PAVM
PAVM is a perceptual metric for the phantom-array effect — the chain of bright dots that appears when a viewer moves their eyes across a hig…
- IEEE 1789-2015
IEEE 1789-2015 is an IEEE recommended practice that defines low-risk and no-effect frequency / modulation-depth thresholds for current modul…
- EU Ecodesign SLR
Commission Regulation (EU) 2019/2020 — the Single Lighting Regulation under the Ecodesign framework — sets ecodesign requirements for light …