1) Product overview
Name: Luminous Friend — children's helmet (bicycle/kid helmet, no battery)
Purpose: Increase safety & night visibility (walking, biking, light scooters) for 6–10 year olds; aesthetically pleasing.
2) Size
Size & form
Target range:
+ Head circumference: 50 – 54 cm (common range 6–10 years old). Grow-With-Me version: 49 → 55 cm (expansion/retraction mechanism).
+ Length (forehead → nape): 24 – 26 cm.
+ Width (ear → ear): 18 – 20 cm.
+ Crown height: 13 – 15 cm.
+ Front-rear brim: 3.5 – 4.5 cm (sun protection brim but does not block vision). The fluorescent fiber border takes up an additional +0.5 cm on the outer edge of the brim as you requested.
+ Foam pad (liner): 1.5 – 2.0 cm thick, many air holes Ø 0.8–1.0 cm (feels “light as a cloud”).
+ Target weight: 220 – 260 g (including padding) — guaranteed “super light”.
3) Materials
A. Outer shell
Main material: Polycarbonate (PC) in vacuum-formed (in-mold) sheet or ABS (hardshell) depending on production options.
Preference for children's bicycle helmets: In-mold PC (thin, light, bonded directly to EPS for lighter weight). PC shell thickness reference ~0.3–0.8 mm (bicycle style). (Motorcycle-type shells are thicker, 3–5 mm.)
Finish: UV-stable coating (to prevent yellowing), non-toxic paint, silk screen printing/HTV logo.
B. Impact absorbing layer (Liner)
Materials: EPS (Expanded Polystyrene) — standard for single-impact energy absorption; or EPP (Expanded Polypropylene) for resilience/multi-impact (more expensive). Many modern helmets use hybrids (different density zones).
Thickness: total liner (main protection area) is usually 15–30 mm (for light bicycle helmets); 15–20 mm air padding is recommended.
Reference EPS density: ~40–80 kg/m³ depending on the area and protection target. (Detailed design requires simulation/testing)
C. Inner cushion/liner (comfort pads)
Cover material: moisture-wicking, antibacterial fabric (CoolMax or bamboo-blend), removable & hand-washable.
Structure: 1.5–2 cm thick cushion, many air holes Ø 0.8–1.0 cm for aeration.
D. Retention system
Chin strap: Nylon webbing 12–15 mm, durable, abrasion resistant.
Buckle: Side-release buckle (polyacetal/nylon), easy to operate with one hand, withstands force according to standard requirements.
Adjustment mechanism: ratchet dial (plastic), or simple pull system for the low-cost version (Grow

-With-Me: 49→55 cm with pull/retract mechanism).
4) Luminous trim — the main part

Two technical options (pros and cons):Phosphorescent material — no battery required
Materials: Glow-yarn / glow-fiber / phosphorescent strip (yarn/strap containing phosphorescent strontium-aluminate powder or textile fiber mixed with luminescent pigment). These materials absorb light (sunlight or lamp) and then glow in the dark for several hours. (For example, commercial glow yarns report charging in a few minutes to 1 hour and glowing for 1–3 hours depending on the type.)
Integration method: pack the fiber or strip into a transparent TPU/PVC channel pressed at the rim edge (in-mold or heat-sealed) — waterproof channel, does not scratch the fiber directly. Size add +0.5 cm as you noted.
Expected performance: after 1 hour of sun exposure, visible luminescence for ~1–3 hours (gradual decrease in intensity); good pigment life (>10–15 years under proper storage conditions, depending on pigment & binder type).

Pros: no batteries/electricity required, safe for kids, low-moderate cost.

Disadvantages: limited brightness; dimmer light than LED; pigment may fade/stain with mechanical exposure/application.

5) Mandatory inspection & testing (according to EN1078 / TCVN/QCVN)
Important tests (independent testing, e.g. QUATEST):
Impact test: free fall on an anvil (flat + kerbstone) at standard speed/height; maximum acceleration measurement must be below standard threshold (EN1078 sets impact limits).
Retention system & roll-off test: test retention force, drop load test to check roll-off (no slipping).
Strap & buckle strength / dynamic test: dynamic load test, tensile test.
Field-of-vision & coverage: standard vision testing.
Marking & info check: labels, instructions, and warnings must be complete according to standards.
Luminescent edge performance: afterglow time measurement after illumination calibration (lux/time report). (Luminescent material testing: durability, washability, abrasion resistance). 6) Lifespan & Warranty
Recommended lifespan: replace after 3–5 years of normal use or immediately after a major impact (EPS may be compressed/degraded). This is a general industry recommendation.
Mips
Luminescent part (phosphor) lifespan: strontium-aluminate pigments can retain their luminescence for many years (many industry sources say >10–15 years if the powder & binder are good). However, the initial brightness and afterglow duration will gradually decrease due to abrasion, dust and UV if not covered well.