I’m looking for a portable way to verify temper stress and spot anisotropy before install, ideally on 10 mm low-iron in daylight; has anyone compared a handheld polariscope to a polarized lens + 6500K LED panel? Goal is consistent, documented readings that map to ASTM C1048 and reduce callbacks from roller wave/anisotropy glare — what setups or calibration routines are you using in the field?
For numbers that tie back to C1048, use a GASP handheld (ASTM C1279) with the daylight hood; zero on an annealed low‑iron coupon and verify monthly on the vendor’s calibration block: GASP Polarimeter - Non-Destructively & Accurately Measure Surface Stress in Soda-Lime Float Glass. Keep your anisotropy visuals with cross‑polar film + a 6500K LED, lock phone WB/exposure and shoot RAW next to a reference strip, then log center/edge surface compression alongside the photo — think torque wrench vs “good and tight.” Do you need edge readings too or just center for your records?
On 10 mm low‑iron in daylight, GASP wins for repeatable numbers; the 6500K panel only holds up if it’s DC‑driven, CRI 95+, and you lock a linear polarizer to a fixed axis. @j_hunter45, have you tried logging incident lux and gray‑card WB to normalize captures — i tag compass orientation and shoot RAW so results map cleanly to C1048 across jobs.
Quick tip: for 10 mm in daylight, work under north-sky or a pop-up shade — direct sun exaggerates fringes and , it’ll lie to you. I log GASP readings as nm retardation and auto-convert to surface stress in a sheet, and I always shoot the eyepiece with a phone + circular polarizer so the report shows the same pattern; the stock hood drifts color, so a quick white-balance card helps. @j_hunt, have you tried the D65 hood kit to stabilize color (https://www.strainoptics.com/gasp-stress-polariscope/)?
Skip the panel — stick a 1/4‑wave retarder and an ND8 clip on your handheld and the fringe order on 10 mm reads clean in daylight. I mark heat‑treat direction, measure 50 mm in from the edge, and grab a phone shot with a 100 mm ruler so the numbers map to “documented readings” for ASTM C1048; @lthompson55, you tried the retarder trick yet?
And i tape an azimuth ring on the handheld and do a quick two‑point check each morning: baseline under a canopy at extinction, then verify with a 550 nm 1/4‑wave plate at 45° (e.g., Thorlabs) so the retardation readout/photos line up with our C1048 docs. If you try a panel, power it from a DC‑only pack and lock WB near D65 or it drifts like a bathroom scale; @jared_wilson42 do you log edge vs center separately?
@OP are you after photos only, or nm values tied to GASP? I get consistent daylight checks with a handheld plus a tiny reference coupon — tape a about 120 nm birefringent film at the edge so you can verify orientation and exposure before each lite. If you go LED, use a high‑CRI 95+ panel with a DC driver; PWM flicker makes fringes “strobe” and kills repeatability.
But on 10 mm low‑iron in daylight, I get repeatable, ASTM‑friendly captures by locking WB/exposure on the phone and slipping a 3D‑printed azimuth collar with a bubble level and 10° detents on the handheld, so every shot hits the same angle and we mark roller direction. If you go the “6500K LED panel” route, use CRI 95+ with a DC driver and a linear polarizer — PWM backlights smear fringe contrast. You chasing photos only, or also surface stress numbers; if the latter, a Strainoptics handheld plus that collar and a quick morning baseline has been solid for us: https://www.strainoptics.com.