Selection & sizing

How to read ripple and flicker specs

Ripple under 5 percent and flicker-free mean different things. This guide separates ripple, flicker, SVM and Pst LM and shows how to read the real figures.

Last updated：2026-11-06

"Ripple under 5 percent" and "flicker-free" are the two most repeated lines on a driver datasheet, yet they name two completely different physical things: one is about how clean the DC output is, the other is about whether brightness jumps in front of the eye. Confusing them means either shipping an ordinary driver into a video shoot, or paying a premium for numbers that do nothing for the site.

The one-sentence rule: ripple is DC purity, flicker is brightness jitter

• Ripple is an AC component riding on the output voltage or current; it is about how clean the DC is, and it drives long-term LED lumen depreciation and color shift
• Flicker is the periodic variation of brightness over time; it is about whether the eye sees a flash, and it is shaped by ripple, dimming method and topology together
• A driver can have very low ripple yet visible flicker at low TRIAC dimming, or modest ripple yet no visible flicker under high-frequency PWM
• What it means for buying: enforce flicker for filming, healthcare and education; enforce ripple for long life and high light quality, and verify each separately

The four metrics and what they measure

Ripple percentage is the most concrete:

ripple % = V_ripple(pp) / V_out x 100%

Example: 120 mV peak-to-peak ripple on 24 V out
    ripple = 120 mV / 24000 mV = 0.5%

Flicker percentage uses brightness, not voltage:

Flicker % = (L_max - L_min) / (L_max + L_min) x 100%

L is luminous flux, not voltage.

Acceptable ranges

The table below is a common engineering threshold set. Note there is no global "flicker-free" definition; when a vendor claims it, ask which metric and under what condition.

Key points:

• Ripple under 5% is the common industrial bar for constant-voltage drivers; filming grade needs 1-2%, usually better output filtering or a linear stage
• Flicker under 8% sits in the IEEE 1789 low-risk band, but only at low frequency; above roughly 200 Hz the eye is insensitive and the bar can relax
• SVM under 1.0 is the "invisible" verdict per IEC TR 63158, a more eye-faithful metric than flicker percentage
• Pst LM at or below 1.0 is the IEC 61000-3-3 limit, mainly bounding the device's flicker disturbance to the grid, not the lamp's own flash

How to pull real numbers from a datasheet

Datasheets rarely list all four; learn to convert and to ask:

1. Find "ripple & noise" or "output ripple": often < 100 mV pp or < 5%. Convert with ripple % = pp / rated voltage. 120 mV pp on 24 V is 0.5%; on 12 V the same 120 mV pp is 1.0% - the same absolute ripple is twice the ratio on a low-voltage system, so 12 V strips deserve extra attention on this item
2. Read "flicker-free" with suspicion: ask three things - which metric (SVM? percentage?), over what dimming range (testing only at 100% brightness is meaningless), at what frequency. A bare "flicker-free" with no data is marketing
3. Read the dimming interface: TRIAC at low end distorts the current waveform badly and pushes flicker percentage past 20%, the top source of on-site flicker complaints (the mechanism is in the truth about TRIAC minimum load)
4. Read the load point: ripple and flicker both shift with load; under light load (below 30%) they often worsen versus rated, so verify at your real load

How dimming changes flicker

The dimming method decides the fate of flicker, which is why a "flicker-free driver" falls over the moment it meets TRIAC:

• TRIAC: phase-cut dimming; at low end the chopped current waveform is severely distorted and flicker percentage easily exceeds 20%, the number one source of flicker complaints
• 0-10V / DALI: analog or digital dimming; a competent driver keeps low SVM across the whole range
• PWM: frequency is the key; high frequency (above 1000 Hz) is imperceptible, low-frequency PWM is itself a flicker source
• Already lit but still pulsing: if the lamp is on yet shows rhythmic bright-dark, go to the flicker troubleshooting tree - that article handles "it is already flickering", not "how to read the spec"

Selection and verification checklist

1. Set the bar by application: general commercial under 8% flicker is fine; filming, operating rooms, classrooms and long eyestrain use need under 3% or lower
2. Ask for ripple and flicker data separately: do not release on the words "flicker-free"; require SVM or flicker percentage with test load and dimming point stated
3. Low-voltage strips watch ripple harder: on 12 V the same absolute ripple is double the ratio, so check ripple mV pp / 12
4. Evidence across the dimming range: require flicker at 100% / 50% / 10%; anything measured only at full brightness does not count
5. Choose dimming method: prefer 0-10V or DALI over TRIAC; if TRIAC is mandatory, confirm the driver has holding-current compensation
6. Trust the family, not the slogan: families labeled flicker-free such as H01 or H02 include that item in outgoing inspection, more reliable than a one-off random check

Power and current conversion, and dimming load math, are done in the LED driver sizing calculator; the glossary guides cover ripple, flicker and SVM term definitions and are outside this article.

© 2026 YFX. Figures are for selection purposes. Always follow the datasheet and local wiring regulations for final installation.