When light hits matter, four things can happen. Reflect off it, get absorbed by it, transmit through it, or refract through it. Every reflector, lens, diffuser and finish in lighting design is engineered around these four interactions.
Four ideas to carry into the next specification conversation you have.
On smooth surfaces (mirror, polished aluminium). On rough surfaces, light diffuses in all directions.
Black surfaces absorb almost everything. The energy doesn't disappear, it becomes heat. Why dark paints raise AC load.
Clear glass transmits ~92%. Frosted glass transmits with diffusion. Opaque materials transmit ~0%.
Light slows in denser media (water, glass, PMMA) and bends. The basis of every TIR lens in modern LED design (EP09).
Light reflectance value (LRV) determines how much light bounces back. Builds on EP14 (Painting & Light).
| Surface | Reflectance | Behaviour |
|---|---|---|
| Polished aluminium | 92% | Specular, mirror-like |
| Matte white paint | 80–85% | Diffuse, bounces all directions |
| Beige carpet | 30–40% | Diffuse, partial absorption |
| Polished marble | 60–70% | Specular, hot reflections |
| Dark grey concrete | 15–25% | Mostly absorbs |
| Black velvet | ~ 2% | Almost total absorption |
| Clear glass (4 mm) | 92% transmit | Transparent, minimal loss |
| Frosted PC diffuser | 70–85% transmit | Diffuse transmission |
Five practical implications for Saudi lighting design.
A polished marble floor reflects light like a mirror, generating hot spots and disability glare. A matte porcelain tile diffuses the same light evenly. Picking finish for a Saudi mall means picking glare risk.
Every photon absorbed by a dark wall becomes heat in the conditioned space. AC removes it. Dark interiors don't just need more light, they need more cooling. This is why Mostadam rewards high LRV.
92% × 92% × 92% = 78% if light passes through three glass layers. Premium fixtures use anti-reflective coatings to recover the missing 22% across optical stages.
When light hits glass or PMMA at the critical angle, it bounces internally instead of escaping. TIR lenses (EP09) use this to channel lumens with > 90% efficiency.
Thin films, oil on water, peacock feathers, colours appear without pigment because different wavelengths interfere. Used in dichroic filters and modern anti-reflective coatings.
Our reflectors specify reflectance %, our diffusers specify transmittance %, our TIR lenses specify refractive efficiency. Every datasheet is honest about the four interactions.
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