Written by Chris Bond, a lighting professional with 18 years of industry experience
CCT, CRI and beam angle are printed on every LED box and every spec sheet, and most buyers either ignore them entirely or get them backwards. This is the "how to actually read a spec sheet" guide — practical and room-by-room, not a physics lecture. It also goes somewhere most competitor content doesn't: light isn't just something you see by, it's a direct physiological input, whether you're aware of it or not — and the last section explains why that's genuinely useful to understand, not just interesting trivia.
Correlated Colour Temperature (CCT) describes the visual warmth or coolness of a light source, measured in Kelvin. Lower numbers look warmer (more amber/orange), higher numbers look cooler (more blue/white).
| CCT Range | Character | Typical Application |
|---|---|---|
| 2700–3000K | Warm, relaxed | Living rooms, bedrooms |
| 3000–4000K | Neutral | Kitchens, bathrooms |
| 3500–5000K+ | Cool / daylight | Task-heavy areas, garages, offices |
In practice, the defaults are more nuanced than a simple lookup table:
Colour Rendering Index (CRI) measures how accurately a light source reveals the true colours of objects, on a scale to 100 — where 100 matches natural daylight perfectly. Below 80 reads as visibly poor. 90 and above is the tier worth calling "great."
Where it matters: kitchens (food colour), bathrooms (skin tone at the mirror), wardrobes and dressing areas (matching clothes accurately), retail and display lighting — anywhere colour accuracy genuinely affects a decision someone's making under that light. For the mirror specifically, CCT and CRI are only half the story — see our guide on lighting a face well in a bathroom for why mirror width and fitting placement matter just as much as the light source itself.
Where it doesn't matter much: garages, general circulation spaces, storage. 80 CRI is fine here — there's no need to pay the premium for 90+ in a space where nobody's judging colour under the light.
| Beam Angle | Character | Typical Use |
|---|---|---|
| ~10–20° | Spot | Accent/feature — highlighting art or a single object |
| ~24–35° | Narrow flood | Benchtops, task areas needing concentrated light |
| ~36–45° | Flood | General room downlighting — the most common residential choice |
| 46°+ | Wide flood | Large open areas, ambient fill |
The mistake that gets made constantly: specifying a flood or wide-flood downlight over a kitchen island or benchtop, then wondering why the task area still feels dim. Beam angle needs to be chosen for the actual task happening at that point, not just the general room type.
Spacing needs to work together with beam angle and ceiling height — too tight and you get an over-lit "runway" look with overlapping hot spots; too wide and you get dark patches between fittings. As a general starting point, spacing roughly equal to the ceiling height gives reasonably even coverage for a standard flood distribution, though this shifts with beam angle and target lux level.
Rather than eyeballing it, the Lux Calculator handles this properly — enter room dimensions, ceiling height and fitting output, and it calculates actual coverage rather than a rule-of-thumb spacing guess.
The "wrong spec" jobs worth talking about usually aren't really about a fitting looking wrong. They're about a spec that fights how the body actually responds to light — and understanding the mechanism changes how you think about CCT choice, not just the visual outcome.
Rods and cones handle vision — what you consciously see. But a separate set of cells in the retina, intrinsically photosensitive retinal ganglion cells (ipRGCs), containing the photopigment melanopsin, don't contribute to conscious sight at all. They feed directly into the suprachiasmatic nucleus — the brain's master clock — and drive non-image-forming responses: melatonin suppression, alertness, pupil response, circadian entrainment.
Light isn't just something you see by. It's a direct physiological input, whether you're aware of it or not.
This is the mechanism behind advice most people have already heard as a vague rule of thumb: "warm at night, cool during the day." Cooler, blue-rich CCT during daylight hours supports alertness, because it mimics daylight — which is genuinely rich in that wavelength. The same blue-rich content in the evening actively fights the body's wind-down, by suppressing melatonin when it should naturally be rising.
This turns a vague suggestion into something with a specific, explainable mechanism — and it's the reason CCT choice for a bedroom or evening living space isn't just an aesthetic decision.
Flicker below roughly 120Hz is linked to headaches, eye strain and fatigue in sensitive individuals — and sensitivity varies significantly between people. Migraine sufferers in particular show markedly higher rates of discomfort from flicker exposure than the general population.
Worth stating plainly: "I can't see it flickering" doesn't mean a fitting-and-driver combination is actually flicker-free for everyone in the room. This is a genuinely useful, non-obvious point when weighing up a budget driver against a quality one — and it ties directly into driver quality, covered in our guide on dimming compatibility and why LEDs fail early.
This section is the summary. For the full picture — the measurement standard behind melanopic effect, the WELL Building Standard's actual benchmarks, what the research says about morning vs evening exposure, and a practical framework for designing to it — see the deep dive: How Artificial Light Actually Affects You — Melatonin, Melanopsin & Designing for the Body Clock.
Once you've settled on CCT, CRI and beam angle, use the Lux Calculator to confirm your fitting count and spacing actually hit the target illuminance for the space.
Open Lux Calculator →