The study investigated the effect of exposure to monochromatic lights (ambient - control, blue, red, yellow, white) on haematology, plasma electrolytes, growth hormone and weight changes in albino rat (Rattus norvegicus). Albino rats were exposed to lights of varying wavelengths (15 watts energy saving fluorescents) from suckling age to 63 days; the light intensity was regulated to 300 lux. An Inverter was used to ensure uninterrupted power throughout the study-period. At the end of 63 days of exposure, blood samples were collected from anaesthetized rats through cardiac puncture into plain bottles (plasma electrolytes analysis) and EDTA-bottles (haematological parameter analysis). Rats were weighed to the nearest gram on a top-loading Metler electronic balance. Packed Cell Volume (PCV), Red Blood Cell (RBC), White BloodCell (WBC) counts, Haemoglobin (Hgb) concentration, Mean Corpuscular Haemoglobin (MCH), Mean Corpuscular Heamoglobin Concentration (MCHC), leukocyte differentialand platelet counts were estimated by standard haematologicalmethods. Spectrophotometry method was used to analyse plasma electrolyte and Growth Hormone (GH). Data obtainedwere expressed as means and standard deviation; means were compared using ANOVA and separated using Duncansmultiple range test at p<0.05. Rat weights were not significantly (p>0.05) affected by exposure to the lights. PCV (%) wassignificantly different (p<0.05); rats exposed to ambient, blue and red lights recorded significantly (p<0.05) higher valuesof 42.35, 40.00 and 36.33 respectively; no significant difference (p>0.05) was recorded in the other blood parameters;plasma electrolyte concentrations showed no significant difference (p>0.05) among the rats. The growth hormoneconcentration was significantly different (p<0.05) with rats exposed to red light having significantly (p<0.05) higher (14.80mg/ml) concentration. Exposure of albino rats to monochromatic lights of varying wavelengths for 63 days had significantimpact on PCV and growth hormone of albino rats.