Glass, film or polycarbonate
Light, insulation, service life and capital cost: the four-way trade that decides a covering.
Light transmission
Single glass transmits roughly 88–91 % of visible light when clean; a 150 μm film starts near 88–90 % and falls as it ages and dusts; 16 mm twin-wall PC starts around 79–82 % and falls faster. In low-light winters the difference is yield, not aesthetics.
Insulation and night loss
Double glass, PC and double film all cut night heat loss. If you heat, insulation is a running-cost decision; if you do not heat, it is a condensation and disease decision.
Service life and replacement cost
Glass lasts twenty-five years and is repaired pane by pane; film is replaced every three to four seasons; PC panels lose transmission over ten to fifteen years. Put the replacement cycle in the ten-year cost.
Where each wins
Glass: high-light, high-value crops with heating and a long horizon. Film: fast, low-capital, seasonal production. PC: cold nurseries and hail-prone sites where insulation and impact matter more than peak light.
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