Loading ...
Until recently, several measures like Flicker Index (FI) and Modulation depth were used to assess the
visibility of flicker and the stroboscopic effect. None of these measures are suitable to predict what
people actually perceive or experience. Flicker and stroboscopic effect visibility are impacted by
modulation depth, frequency, wave shape and duty cycle, and these measures do not take into account
all these parameters. Therefore, scientific models have been developed based on the Human Visual
System, referring to the visual perception of humans, which is the part of the nervous system that allows
us to see. A more robust TLA measure for flicker is P
st
LM
, and for the stroboscopic effect SVM [1,2]. These
measures are supported by Lighting Europe [3] and NEMA [4] and are used in the assessment of Philips
branded EyeComfort LED lighting of Signify. Continuous improvements on TLA measures are currently
investigated.
The usual definition of the absolute visibility threshold is the point where the observer can detect the
percept 50% of the time [2]. This means that a person is not sure whether or not he/she sees the flicker
effect and chooses to respond with āI see in 50% of the timeā. It is not that the observer will have a clear
idea of seeing flicker 50% of the time and clear idea of not seeing the other 50%. Rather instead,
the
50% level is the level where the decision of whether or not to see is at chance.
Given the above, the requirement for no visible flicker is defined as P
st
LM
ā¤1,0 and is based on IEC 61000-
4-15 [53] and NEMA 77-2017 [54]. Measurement of P
st
LM
is done according to IEC TR 61547-1, edition 2
[52].
Why should we care about Flicker and the Stroboscopic effect?
Lighting products which exhibit flicker or the stroboscopic effect are considered as lower quality lighting
[5-14]. TLAs are not only annoying for people but also have impact on the comfort of the eye, general
comfort and visual performance. More specifically, visible TLAs can decrease visual task performance,
cause eye discomfort (tired eyes), increase headache occurrence, eyestrain, and cause annoyance.
Studies show that visible flicker can trigger epileptic seizures in certain cases [5-14]. With this in mind,
Philips branded EyeComfort LED products of Signify have been designed to minimize visible flicker and
stroboscopic effect.
2. Photobiological safety
Blue light hazard
The blue light hazard is a photochemical damage of the retina and depends on the spectral composition,
intensity and time of exposure to the eye. The International Electrotechnical Commission (IEC) has
developed a standard for evaluating Photobiological safety [16]. The sources are classified in 4 risk
groups (0 = no risk, 3 = high risk).
Risk Group 0: The lamp poses no photobiological hazard
Risk Group 1: No photobiological hazard under normal behavioral limitations
Risk Group 2: Does not pose a hazard due to aversion response to bright light or thermal discomfort
Risk Group 3: Hazardous even for momentary exposure
A common misunderstanding in the media is the idea that LED lighting contains higher portions of blue
wavelengths and is therefore more likely to cause blue light hazard. This has been researched and
measured thoroughly by the Global Lighting Association, comparing spectral content of different lighting
technologies and the above-mentioned standard, together with the input of many scientists [15].
Loading ...
Loading ...
Loading ...