| CRUMBLE | Speed of light and then boom and collapse (7) |
| OTHELLO | "Put out the light, and then put out the light" speaker |
| LANTERN | Light, so aren't moving in line regularly? (7) |
| PHLOGISTON | Soft light so weird on something in fire? |
| SPARTAN | Boom and bust leaving business with an austerity champion |
| ASTOUND | Stagger to us and collapse (7) |
| DEBACLE | Bleed badly, clutching middle of back, and collapse |
| CRUMPLE | About to become wrinkled and collapse (7) |
| TWOFOLD | Double II and collapse (7) |
| BRADLEY | Scientist known for his discovery of the aberration of light and for observing the oscillation of Earth's axis (nutation), who succeeded Edmond Halley as Astronomer Royal in 1742 (7) |
| DRAGAND | Take forever and collapse from exhaustion in screen action (4,3,4) |
| PASSOUT | Distribute and collapse (4,3) |
| DOPPLER | Christian -, 19th-century mathematician and physicist noted for his work an the frequency of light and sound waves (7) |
| UVEITIS | Requiring a kind of light and energy, it is an eye problem (7) |
| SUNBEAM | Amen! Bus turned up - source of light and joy (7) |
| FOLDSUP | Doubles over and collapses (5,2) |
| NEVADAN | Statesman, one that runs through St Petersburg, and collapses |
| MOCKED | Took off from Mayo at the speed of light - and half-packed (6) |
| PRINCETON | Where Einstein taught text about grasping the speed of light and energy (9) |
| FRESNEL | Physicist who helped establish the wave theory of light and invented a lens used in lighthouses (7) |
