How to Read a Light Fixture Spec Sheet: IP, CRI, UGR and Lumens Explained
6 min reading time
IP44 by the basin, IP65 outdoors, CRI 90+ for interiors, UGR under 19 at work areas and 100+ lm/W from a good LED. A plain-English guide to every number on a light fixture datasheet.
In short: the IP rating tells you how well a fixture resists dust and water (IP44 minimum near a basin, IP65 for showers and outdoor areas), CRI shows how faithfully light renders colour (specify 90+), UGR measures glare (keep it under 19 wherever people work or read), and lm/W tells you how much light you get per watt of energy (a good LED delivers 100+). Below we decode every number on a spec sheet — and give you the exact values to specify for each space in a villa, hotel or restaurant.
Why the spec sheet matters
A fixture datasheet is a dozen abbreviations, and those abbreviations decide whether a wall light survives a steamy bathroom, whether food on a restaurant table looks appetising or grey, and whether a downlight glares over a desk. Reading them is easier than it looks: only five parameters really matter.
The five numbers that decide everything
Everything else on the sheet is secondary.
IP — ingress protection: how sealed the fixture is against dust and water
CRI (Ra) — colour rendering index: how honestly the light shows colour
Kelvin (K) — colour temperature: the warmth or coolness of the light
UGR — unified glare rating: whether the fixture dazzles
lm/W — luminous efficacy: how much light you get per watt
Wattage on its own tells you almost nothing. Watts measure how much energy a fixture consumes; lumens measure how much light it actually produces.
Watts vs lumens: the classic confusion
Always compare fixtures by lumens, never by watts.
A 10 W LED produces roughly 1,000 lm — about the same as an old 75 W incandescent bulb
A good LED delivers 100–160 lm/W
Rooms are calculated in lumens per square metre of floor area, not in watts
The parameters, one by one
What each abbreviation means and which values to choose.
IP: protection against dust and water
Two digits: the first is protection against solid particles (0–6), the second against water (0–9). The closer a fixture sits to water — or to outdoor humidity and rain — the higher the second digit needs to be.
IP20 — dry interior rooms: living rooms, bedrooms
IP44 — bathrooms (basin and mirror zone), kitchens, covered terraces
IP65 — shower zones, facades, gardens, open terraces
In a bathroom, always check the installation zone: directly above a shower you need IP65, while beside a mirror IP44 is enough. In a tropical climate, treat the terrace and any semi-outdoor space as a wet zone — IP44 is the floor, not the ceiling.
CRI and Kelvin: quality and warmth of light
CRI (Ra) shows how natural colours look under the light — 100 is the daylight reference. Kelvin sets the tone: the lower the number, the warmer the light.
2700–3000 K — warm and inviting; 4000 K — neutral working light
Cheap LEDs at CRI 70–80 turn food grey and skin sallow. Saving money on CRI is a saving your guests will see every single evening.
UGR and lm/W: comfort and efficiency
UGR is the unified glare rating: the lower the number, the more comfortable the fixture is for the eyes. lm/W tells you how much light you get for every watt drawn from the grid.
Bathroom — IP44 at the mirror, IP65 in the shower zone, CRI 90+, 3000 K
Office, study — IP20, CRI 80–90, 4000 K, UGR < 19
Terrace, garden, facade — IP65, 2700–3000 K
Retail, display, gallery — CRI 95+, accent optics
Common mistakes when reading a datasheet
The traps people fall into most often.
Comparing watts instead of lumens
Fitting IP20 in a bathroom — corrosion and short circuits follow within months
Ignoring CRI — the whole interior turns grey the moment the lights come on
Skipping UGR on spots above tables and desks — glare and eye strain
Trusting the "100 W equivalent" claim on the box instead of the actual lumen figure
Frequently asked questions
What does the IP rating of a light fixture mean?
It is the degree of protection of the housing: the first digit covers dust (0–6), the second covers water (0–9). IP20 is fine for dry interior rooms, IP44 for bathrooms and covered terraces, IP65 for showers, facades and gardens.
What is CRI and which value should I choose?
The colour rendering index: how natural colours look under the light, with 100 as the daylight reference. Specify CRI 90+ for homes and restaurants, and 95+ for retail displays and art.
What is UGR?
Unified Glare Rating — a measure of how much a fixture dazzles. The lower, the more comfortable. For workstations and offices, keep UGR below 19.
Which matters more: watts or lumens?
Lumens. Watts show energy consumption; lumens show light output. A modern 10 W LED delivers around 1,000 lm — the same as a 75 W incandescent bulb once did.
Which fixtures can be installed in a bathroom?
IP44 or higher by the mirror and basin, IP65 in the shower zone and above the bath. Ordinary IP20 fixtures corrode and fail quickly in humid rooms — especially in a tropical climate.
What does lm/W mean?
Luminous efficacy — how many lumens a fixture delivers per watt. 100–130 lm/W is a good level, 140+ means top-tier chips. The higher the figure, the lower your electricity bill for the same amount of light.
Specify the right fixtures for your project
RODESIGNE designs and manufactures custom lighting for villas, hotels and restaurants — in Phuket and worldwide. We select or build fixtures to the exact IP, CRI and optics your project needs, from a single statement pendant to a full technical layout. Explore our Technical & Architectural Lighting services or request a project estimate — send us your plans and we will take it from there.
