What is the best alternative to Lux Light Meter Pro on iPhone?

Photone - Grow Light Meter, S tier, #1 in light metering.

Is there a free alternative to Lux Light Meter Pro?

Yes: Photone - Grow Light Meter (S tier, #1) is free to download, with in-app purchases.

Yes. 3 apps rank above it in light metering: Photone - Grow Light Meter (#1), Light Meter LM-3000 (#2), Photo Light & Exposure Meter (#3).

Lux Light Meter Pro is B tier, #4 of the 6 tiered apps in light metering. Here is everything that competes with it on iPhone, in tier order.

1
Photone - Grow Light MeterShigher tier
Free + IAP · ★ 4.6 · 7,242 ratings · score 93
Turns an iPhone or iPad into a PAR meter that measures plant light as PPFD, DLI, lux, foot-candles and color.
2
Light Meter LM-3000Ahigher tier
Free + IAP · ★ 4.5 · 4,584 ratings · score 89
Measures illuminance (lux or foot-candles) and correlated color temperature (Kelvin) using the iPhone's front-facing.
3
Photo Light & Exposure MeterAhigher tier
Free + IAP · ★ 4.5 · 4,437 ratings · score 89
Light meter that suggests exposure settings in real time and measures shutter speed, lux, EV and color temperature.
5
myLightMeter PROC
$4.99 · ★ 4.8 · 2,864 ratings · score 67
Exposure light meter for film and digital photography with manual controls, metering modes, and session logging.
6
Lightme - LightmeterC
Free + IAP · ★ 4.8 · 951 ratings · score 67
Lightmeter app showing multiple aperture and shutter combinations, with spot, continuous and pinhole metering modes.

What is the best alternative to Lux Light Meter Pro on iPhone?: Photone - Grow Light Meter, S tier, #1 in light metering.
Is there a free alternative to Lux Light Meter Pro?: Yes: Photone - Grow Light Meter (S tier, #1) is free to download, with in-app purchases.
Does anything rank above Lux Light Meter Pro?: Yes. 3 apps rank above it in light metering: Photone - Grow Light Meter (#1), Light Meter LM-3000 (#2), Photo Light & Exposure Meter (#3).