Free tool · nothing leaves your browser
Your sunny window is probably a cave.
Your eyes adapt to darkness without telling you. A windowsill that feels bright often delivers a tenth of what a tomato needs — which is why seedlings stretch, pale, and flop, and why most people blame the seed.
This measures the thing you cannot see: the Daily Light Integral, the total dose of photons your windowsill delivers in a day. It is the number commercial growers plan around. Set your window below and find out what you are actually working with.
Describe your window
How this is calculated
Solar position comes from standard declination and hour-angle geometry for your latitude. Clear-sky beam irradiance uses a Meinel air-mass attenuation model, then gets transposed onto a vertical surface at your window’s orientation, with sky-diffuse and ground-reflected components added. Glazing transmittance, obstruction horizon, blind position and your distance back from the glass all reduce it. Total solar energy converts to photosynthetic photon flux at roughly 45 percent PAR fraction and 4.57 µmol per joule, then integrates across the day.
What this is and is not
This is a physical model, not a meter reading. It will not capture a neighbour’s white wall bouncing light in, a skylight, or last week’s weather. Treat it as a well-grounded estimate, accurate enough to tell a workable windowsill from a hopeless one — which is the decision that actually matters.
Nothing is transmitted. There is no analytics, no account, no storage, and no server. The whole calculation happens in your browser and stops when you close the tab.
Found out your window works?
Every kit ships with hand-picked non-GMO seeds, Premium Nutrient-Rich Potting Soil, a 100% Recyclable Planter, and a guide written by a grower.